Chapter 3c Neuromuscular Disease and Electrodiagnosis

3.3 Neuromuscular Disease and ElectrodiagnosisEllen Sobel, DPM, PhD

Neuromuscular DiseaseUpper motor neuron disorders are caused by lesions in the brain and spinal cord proximal to the anterior horn

cell, clinically resulting in spastic paralysis (Table 1).

Table 1. Differences Between Upper and Lower Motor Neuron ParalysisUpper Motor Neuron Lower Motor Neuron Muscles affected in groups Individual muscles may be affected Atrophy slight and due to disuse Pronounced atrophy to 80% of muscle bulk Spasticity with hyperactivity of Flaccidity and hypotonia of affected muscles and deep tendon reflexes loss of deep tendon reflexes Sensation usually intact, with motor Loss of sensation usually happens and may be more symptoms predominant apparent than motor symptoms such as with diabetic

neuropathy Normal nerve conduction studies Abnormal nerve conduction studies; denervation No denervation potentials in EMG potentials (fibrillations, fasciculations) in EMG Examples: Stroke, cerebral palsy, multiple Peripheral neuropathy, charcot marie tooth disease,sclerosis, brain tumor, spinal cord tumor poliomyelitis, muscular dystrophy

The CNS controls the motion of the peripheral nervous system. Disruption of CNS control over the peripheral

nervous system results in a jerky uncoordinated motion known as spasticity. Stroke and cerebral palsy are common

spastic neuromuscular disorders. Lower motor neuron disorders involve pathology from the anterior horn cell

extending distally to the peripheral nerve, neuromuscular junction, and muscle. Lower motor neuron diseases clini-

cally manifest with flaccid paralysis. Examples of lower motor neuron disease include polio, CMT, and muscular

dystrophy.

Neuromuscular disorders can also be grouped on the basis of inherited and acquired. Inherited neuromuscular

disorders involving the foot include Charcot-Marie Tooth Disease and muscular dystrophy. Acquired neuromuscular

disorders involving the foot and ankle include stroke, cerebral palsy, and head and spinal cord injury.

The quickest way to clinically assess UMN from LMN disease is to test the deep tendon reflexes. Recall the deep

tendon reflexes are graded as:

• 1/5= hypotonic

• 2/5= Normal

• 3/5= hypertonic

• 4/5=clonus

• 5/5=tonus

UMN diseases result in increased tone (3/5-5/5) of the deep tendon reflexes.

Orthopedics | Neuromuscular Disease and Electrodiagnosis 119

Muscle TestingMuscle testing is critical in the evaluation of the neuromuscular foot since most neuromuscular disease is asso-

ciated with significant muscular imbalances and weakness. Muscle power is graded as:

• 0/5= absence of voluntary muscle contraction

• 1/5= Muscle contracture without movement (twitch)

• 2/5=Movement with gravity eliminated

• 3/5=Movement against gravity

• 4/5=Movement against gravity and partial resistance

• 5/5=Movement against gravity and against full resistance

With a tendon transfer, the muscle will lose at least one grade of muscle strength

Coleman Block TestThe Coleman Block Test assesses hindfoot flexibility independent of forefoot position. Is the hindfoot varus

compensatory to forefoot valgus? A 1-inch high block is placed under the lateral forefoot while the Patient is stand-

ing. If the hindfoot rotates out of varus, the varus deformity is flexible and secondary to the plantar-flexed 1st ray.

The hindfoot varus will correct with appropriate forefoot surgical correction. If the hindfoot does not rotate out of

varus with the lateral block, then the hindfoot varus is rigid and a lateral calcaneal closing wedge osteotomy is

indicated.

Stroke

Cerebrovascular disease or stroke refers to all vascular disorders of the brain and is the most common neurolog-

ical disorder with claiming 500,000 victims per year. Stroke is caused by cerebral thrombosis in three-quarters of

cases. Cognitively, stroke frequently results in impaired thinking, decreased learning ability, loss of short-term mem-

ory, and loss of ability to perform previously learned actions (apraxia). Lesions in the left hemisphere cause inability

to speak (aphasia). Acute stroke results in spasticity and weakness, which generally peaks after several weeks. Lesions

on one side of the brain result in motor involvement in the opposite extremity. The most common pattern of motor

involvement is spastic hemiplegia, which involves paralysis of both the upper and lower extremity on the same side

of the body. Usually the upper extremity is more affected. Recovery of motor function when it does occur takes

place within six months.

The foot takes on equinovarus posturing in the stroke patient, which may result in pain, callosities, and ulcera-

tions of the prominent lateral malleolus and 5th metatarsal head/styloid process area. The equinovarus foot type

causes overpull of the long flexors of the foot, which results in severe digital contractures including: hammered hal-

lux, hammer toes, mallet toes, claw toes and clinodactyly. Painful hard and soft corns and ulcerations may develop

over the proximal phalangeal joint of contracted digits and in between the toes. Nails frequently become mycotic

and dig into the skin.

Primary emphasis in stroke rehabilitation is to prevent contractures from forming. A contracture is defined as

fixed shortening of soft tissues with stiffness and loss of elasticity resulting in loss of motion of surrounding joints.

Contractures develop following joint immobilization secondary to severe spasticity or paralysis. Mobilization of the

spastic lower limb with passive joint manipulation will prevent joint contractures from forming. Once the joint is

stretched with passive range of motion exercises, the stretched position must be maintained by splinting. Muscle

tone can also be decreased with systemic pharmacologic agents such as baclofen and diazepam and local motor

nerve blocks with lidocaine or phenol.

Approximately 75% will regain some level of ambulation. The post-stroke patient walks with a circumductory

gait. Significant spasticity is usually present in the stroke patient and generally involves treatment with a solid ankle

foot orthosis of plastic or metal variety.

120 The 2005 Podiatry Study Guide

Head Trauma

There are 500,000 victims of head trauma each year, frequently involving young adult males. Initial treatment

entails physical, occupational, and speech therapy with stretching, serial casting, splinting, and occasional nerve

blocks for modulating hypertonicity. After 18 months, spontaneous recovery is thought to be uncommon. Patients

may require an AFO for accommodation of spastic equinovarus foot deformity. The equinovarus foot with claw toes

may be corrected with Achilles tendon lengthening, split anterior tibial tendon transfer, and intrinsic and extrinsic

toe tendon release.

Multiple Sclerosis

Multiple sclerosis (MS) is the most common central nervous system disease among young adults. The disorder

is present in both the brain and the spinal cord and is characterized by scattered areas of myelin degeneration, which

causes disruption in the smooth flow of electrical messages from the brain to nerves throughout the body. There is

current evidence that the pathogenesis of MS is an autoimmune reaction, possibly involving a virus.

The presenting complaint may be visual disturbances, foot drop, weakness of the lower extremities, gait difficul-

ty, or spasticity. As the disease progresses the patient is frequently overwhelmingly fatigued. Muscle weakness, spas-

ticity, tremor, and gait disturbances become apparent. Sensory manifestations include numbness, paresthesia, verti-

go, blurred vision, and diminished hearing. The diagnosis of MS is made by the presence of abnormal protein in the

cerebrospinal fluid, an abnormal evoked brain response examination, and abnormalities on MRI.

Orthopedic treatment consists of appropriate bracing to provide joint stability and canes and crutches to aid

ambulation. An important part of treatment of MS is pharmacological. Immunosuppressants control the inflamma-

tion that accompanies demyelination. Methylprednisolone is given intravenously and orally to reduce plaque forma-

tion in the central nervous system. Muscle spasms are a major problem for many patients with MS. These are treated

with the common drugs such as liorisil (Baclofen), diazepam (Valium), clonazepam (Clonopin) and cyclobenza-

prine (Flexeril). Pain, fatigue, and depression are controlled with amitriptyline (Elavil), imipramine (Tofranil), and

carbamazepine (Tegretol).

Cerebral Palsy

Cerebral palsy (CP) is a group of nonprogressive brain-damaging disorders affecting 1–5/1000 infants. Cerebral

palsy affects 1% to 2% of all children. One-third of neonates weighing less than five and one-half pounds show signs

of this disease. The main forms of CP are:

• Spastic CP, which is most common affecting about 50-65% of individuals

• Athetoid CP affects approximately 20% of patients with CP

• Ataxic CP affects 15% of CP patients

See Table 2 Motor Symptoms on page 114 for a glossary of motor problems in CP and other neuromuscular

disease.


Table 2. Motor SymptomsSymptom Description PHASIC Normal muscle activityPARESIS Weakness, minimal muscle activityPARALYSIS Complete absence of muscle activitySPASTICITY Increased muscle tone and hyperactive deep tendon reflexMONOPLEGIA Weakness or paralysis of all the muscles of one limb, should not be used to refer

to muscle loss caused by damage to a single nerve or motor rootHEMIPLEGIA Paralysis involving arm, leg, and sometimes face on one side of the body, most

common form of paralysis; usually as a result of upper motor neuron disease PARAPLEGIA Weakness or paralysis of both legs, most commonly result of spinal cord diseaseQUADRIPLEGIA Weakness of all four extremitiesDIPLEGIA Special form of quadriplegia in which legs are affected more than the arms CONTRACTURE Stiffness, loss of elasticity, and fixed shortening of soft tissue resulting in loss of

motion of surrounding jointFASCICULATION Visible twitches of muscle fascicles under the skinTREMOR Involuntary, rhythmic oscillatory movementsATHETOSIS Slow writhing movements of the fingers, hands, toes, feet

The diagnosis is based on delayed milestones and a history of low birth weight and prematurity. Cerebral palsy

can involve an ipsilateral arm and leg (hemiplegia), both legs, most common presentation with low birth weight

(diplegia), or total involvement (quadriplegia). The total involvement form frequently includes scoliosis, hip dyspla-

sia, and mental retardation. Learning disability, visual or hearing impairment, and seizures may be present in the CP

child. The child is usually born hypotonic, but spasticity develops after the first year of life with hypertonic deep

tendon reflexes.

Equinus deformity results from gastrocnemius-soleus spasticity and manifests as a toe-walking gait in the

younger child or a back-kneed gait in the older child. Equinovalgus is most common in diplegia and equinovarus is

most common in hemiplegia. Equinovarus is caused by spasticity of both the posterior tibial muscle and the gas-

trocnemius-soleus muscles. Valgus foot deformity results from a combination of peroneal muscle spasticity and gas-

trocsoleus muscle spasticity. The lower extremity in cerebral palsy at the hip is internally rotated, adducted, and

flexed. The knee may be slightly flexed due to hamstring tightness. Tightness of the hip adductor muscles, hamstring

muscles, together with tight spastic posterior leg muscles, result in the characteristic crouch gait with scissoring at

the hips and toe-walking.

Drop foot results from excessive strength of the plantarflexors or weakness of the dorsiflexors. Adaptive short-

ening of the gastrocnemius and soleus muscle in conjunction with contraction of the posterior capsule of the ankle

and subtalar joint and thickening of the neck of the talus will create a fixed ankle equinus deformity. Equally impor-

tant are contractures of the hamstrings and hip adductors resulting in a scissoring toe-walking gait pattern.


Diagnosis of Cerebral PalsyMost children with cerebral palsy are diagnosed during the first year of life. The patient’s medical history may

reveal prematurity, a floppy baby, and developmental delay in motor milestones. Delayed milestones are important

in making the diagnosis. Normal head control occurs at approximately three months, sitting independently by six

months, crawling at nine months, standing at twelve months, and walking by twelve to fifteen months.

Other common abnormalities include fisting after 3 months of age and a specific hand preference prior to 1

year of age. On physical examination spasticity, hyper-reflexia and toe-walking or the presence of a “crouched” gait

may be present. A child walking on the outer border of the foot may have a varus foot, common in patients with

spastic hemiplegia. The foot and leg are likely to be smaller on the more neurologically disturbed side.

Physical therapy and orthoses continue to be the primary conservative treatment for control of dynamic equi-

nus in children with spastic cerebral palsy. Physical therapy performed on a daily basis may prevent the development

of muscle and joint contractures. Casting is beneficial in the reduction of both muscle tone and contractures espe-

cially for ankle equinus. An articulated AFO may improve gait. Surgically lengthening the contracted Achilles tendon

is an important part of treatment and generally performed in childhood ages four to seven.

Figure 1. Scissor Gait

Poliomyelitis

Anterior poliomyelitis is a viral infection resulting in isolated damage to the anterior horn cell. Damage to the

anterior horn cells results in flaccid paralysis of the muscles innervated by the affected motor cells, however, there is

sensory sparing. The extent of paralysis varies from weakness of one muscle to complete paralysis of all four limbs

and the trunk. If the brain stem is affected, the muscles of respiration become paralyzed as well. In 1954, an oral

vaccine was produced which largely eradicated polio, however, polio is still common in Third World countries. The

acute stage of polio lasts up to four weeks and heralds the onset of flaccid paralysis. The second stage of polio is the

stage of convalescence and recovery and is where spontaneous recovery occurs, which can last up to two years.

Recovery depends upon the condition of anterior horn cells that innervate the muscles. Anterior horn cells that have

been damaged, but not destroyed, may recover their physiologic function and there will be a partial or complete

return of muscle power, depending on the relative number of motor cells that recover. If all the neurons that inner-

vate a particular muscle are destroyed, that muscle may be permanently paralyzed. Destroyed cells can never be

repaired or replaced. However, after illness, muscle strength can be partially recovered as a result of reinnervation by

other motor units to denervated muscle, hypertrophy of some of the surviving innervated muscle fibers, or myofiber

type transformation. Seventy-five to 85% of patients with good orthopedic care show marked spontaneous

improvement or recovery of muscle function.


Figure 2. Child Polio

The final stage of polio is the residual stage in which any remaining paralysis will be permanent. Paralyzed mus-

cles are replaced by fibrous tissue. Any spinal segment may be affected, but the brunt is usually L2 through S1 and

therefore paralysis is most common in the lower limb in 80 to 90% of cases. The arms are involved in about 30% of

polio patients.

Slowed bone growth in the vicinity of paralysis accounts for the common limb length discrepancies observed in

the disease. Significant limb length difference occurs in one-quarter of individuals who have had polio, usually not

greater than 1 inches, but can be as great as three to four inches. Patients with large limb length differences benefit

from external lifts on the entire sole of the shoe. When the muscles surrounding a joint are paralyzed, the joint

becomes flail and unstable and likely to stretch and dislocate, such as in severe genu recurvatum. Genu recurvatum

is the most common bracing problem at the knee and occurs to avoid collapse of the knee during standing because

of weakened quadriceps.

The foot may take one of several positions in polio. Ankle instability and footdrop (or heel drop) caused by

paralysis of the anterior tibial muscle. A calcaneus foot (rearfoot cavus) is a characteristic polio foot type and is

caused by paralyzed triceps surae with strong tibialis anterior and strong invertors and evertors. The calcaneal pitch

angle may be greater than 30˚. The heel may be in severe varus or valgus. When the invertors of the foot are para-

lyzed, the foot goes into extreme valgus. Valgus deformity results from gravitational forces produced by bearing

weight on a flail foot.

Figure 3. Old Polio Legs

Post-Polio Syndrome

In polio survivors ten to forty years after recovering from acute polio, many individuals are now complaining of

several new problems attributed to their former illness. The post-polio syndrome is a set of symptoms, which con-

sists of fatigue, new progressive muscle weakness, and atrophy and muscle pain. It has been estimated that as many


as 80% of polio survivors might experience the disorder. The etiology of post-polio syndrome is postulated to be

decompensation of the balance between denervation and reinnervation after a generalized neuronal disease where

the remaining motor neurons can no longer maintain new sprouts and denervation exceeds reinnervation.

Diagnosis is by exclusion because no test is specific for post-polio syndrome.

Post-polio syndrome is commonly associated with deconditioning, obesity, gait disturbance, and disturbances

in activities of daily living. Patients experience new difficulties with walking and ascending stairs. Gait disturbances

commonly occur in patients who previously used ambulatory aids, such as canes, crutches, or braces, and then dis-

carded them. The cause of these gait problems is progressive weakness, pain, osteoarthritis, and joint instability

resulting from weakened muscle, strain on ligaments, and malalignment. The patient should return to their former

brace or cane, but patients often refuse to do this because they do not want to “give in” to the disability. If the

patient does consent to use a cane or crutch, it is necessary to evaluate shoulder function first to avoid strain on this

frequently weakened joint. Patients with post-polio syndrome have been found to benefit from a carefully selected

exercise program, rest for the exercised muscle group, and the use of an orthosis. Patients with the least neuronal

activity may need to return to a motorized wheelchair.

Myelodysplasia (Spina Bifida)

Spina bifida is an opening in the spine most commonly affecting the lumbar and sacral levels. Spina bifida with

meningocele involves the meningeal sac protruding through an open neural arch vertebral defect and extends to the

subcutaneous layer. Spina bifida with myelomeningocele involves other elements of the spinal cord and nerve roots

protruding through the open vertebral defect. Myelocele is the most severe form involving even the skin failing to

enclose the cord protrusion. Spina bifida occulta involves the neural arches of the vertebra being not completely

closed, however, all of the spinal cord is within the spinal canal.

Figure 4. Spina Bifida

Spina bifida results in paralysis, complete lack of sensation, often with paralysis of urinary and anal sphinctors.

Patients develop foot ulcers from the lack of sensation and various foot deformities occur from the muscle balances,

which are created including teratologic clubfoot and vertical talus, which is actually more commonly associated with

spina bifida than occurring as an isolated deformity. Equinovarus is the most common foot deformity in spina bifida.

Peripheral Neuropathy

The two most common causes of peripheral neuropathy in the United States are diabetes mellitus and alco-

holism. Trauma and entrapment are common, but considered in the differential diagnosis of mononeuropathies.

The most frequent pattern of polyneuropathy is seen with metabolic diseases such as diabetes mellitus, nutritional

deficiency, and renal failure. Neuropathy develops slowly, often over months or years, and begins with sensory

abnormalities in the lower extremities. Sensory loss manifested as numbness, tingling, muscle weakness, atrophy,


and diminished deep tendon reflexes are the hallmarks of peripheral neuropathy. Pain when present tends to be

worse at night.

Most neuropathies give rise to a mixed sensorimotor disturbance, therefore, the patient will experience weak-

ness as well as loss of sensation usually described as numbness. The first manifestation in symmetrical polyneu-

ropathies are usually in the legs, and the legs are involved more than the arms. Distal muscle involvement occurs

more frequently than involvement of proximal muscles. Peripheral neuropathy involves muscles of extension and

abduction such as the anterior group leg muscles and the peroneal muscles. Therefore, drop foot and weakness in

eversion are much more common than weak posterior group muscles. Paresthesias are usually described as numb-

ness, tingling, buzzing, or a feeling of constriction.

Peripheral neuropathy may be confused initially with myopathic disease since both kinds of disorders may

involve varying degrees of weakness with diminished or absent reflexes. Peripheral neuropathy is distinguished from

myopathic disease by its predominantly distal muscle involvement where as myopathies tend to affect the proximal

muscles of the pelvic and pectoral girdle. Also myopathies, in contrast with peripheral neuropathies, do not have a

sensory component (Table 3).

Table 3. Comparison of Neuropathy and Myopathy

Condition Neuropathy Myopathy Anatomical location Weakness of distal muscles, Weakness of proximal muscles

(Foot dorsiflexors, foot intrinsics,hands, and arms)

Sensory Sensory loss present often worse Sensation remains in tact than motor loss. Sensory loss may be present with no motor loss at all.

Atrophy Severe atrophy of calf, hands, Pseudohypertrophy of calves and feet. with fibrous tissue and fat

replacing musclesDeep Tendon Reflexes Diminished NormalExamples Diabetic neuropathy, Charcot- Muscular dystrophy, myositis

marie tooth disease, Guillain Barre Syndrome

Exceptions Myotonic dystrophy-adult inherited muscular dystrophy affects distal muscles present with foot drop

Charcot-Marie Tooth Disease (CMT)

Charcot-Marie Tooth Disease is the most common inherited sensorimotor symmetrical neuropathy usually

beginning in late childhood and is characterized as slowly progressive over years with insidious onset. It is usually

inherited as an autosomal dominant trait, but can be inherited dominantly, recessively, or sex-linked. Neurologic

deficits are symmetric. There is both sensory and motor loss as the name Hereditary Sensory Motor Neuropathy

implies, but the motor loss is much worse. It is characterized by progressive distal muscle wasting and weakness, are-

flexia and cavovarus foot deformities. Patients with CMT disease present most frequently with pes cavus (85% of

cases), drop foot, and severe calf atrophy (stork legs). There is severe slowing of nerve-conduction velocities.

Muscle weakness begins in the foot intrinsic muscles, and then extends to the peroneus brevis and then the tib-

ialis anterior muscle. The gastroc-soleus muscle is the last to be affected. Loss of sensation is present in the feet and

hands and is usually mild.


The characteristic foot in CMT consists of cavus foot with anterior equinus with equinocavovarus with ham-

mered or cocked-up hallux.

Figure 5. CMT Cavus

Dejerine Sottas Disease(Hypertrophic Interstitial Polyneuropathy) or Hereditary Sensory Motor Neuropathy III, is similar, but more

severe than CMT. There is distal muscle weakness of the lower extremities with associated sensory deficit anddecreased deep tendon reflexes. The most distinctive feature of this disease is palpable and sometimes visibleenlargement of the peripheral nerves. Nerve biopsy (usually sural nerve) will confirm the diagnosis.

Refsum’s Disease(Type IV Hereditary Sensory motor neuropathy) is caused by abnormal lipid metabolism and results in accu-

mulation of phytanic acid in the serum up to 50 times greater than normal. Associated findings include ichthyosis,night blindness, and preceding febrile illness. Peripheral muscle weakness, areflexia, dropfoot, pes cavus, and clawtoes are also observed.

Hereditary Spastic Paraplegia(Type V Hereditary Sensory Motor Neuropathy). This is the only form of HSMN that clinically manifests as a

spastic deformity and is inherited as an autosomal dominant disease. There is no sensory component.

Roussy Levy SyndromeRoussy Levy Syndrome is also similar to CMT disease, with the addition of an essential tremor that is most

prominently expressed in the hands. This is a familial, slowly progressive, symmetrical neuromuscular disease.Clinical findings include areflexia, intrinsic pedal muscle atrophy, pes cavus and claw toes, clumsy gait and poorequilibrium, and the presence of the previously noted essential tremor.

Friedreich’s AtaxiaFriedreich’s Ataxia is a spinocerebellar degeneration causing hypertonicity and ataxia. It is caused by autosomal

recessive inheritance. The onset is childhood or adolescence. Hallmarks of this disease include ataxia, cavus foot,clawtoes and kyphoscoliosis.

Diabetic NeuropathyDistal symmetrical sensorimotor polyneuropathy is present in approximately 25% to 60% of people with

diabetes mellitus. Diabetic peripheral neuropathy is a progressive neuropathy, initially involving the more distal


parts of the lower extremities and then progressing centrally to involve the hands, thighs, and in severe cases thetrunk. The major symptoms consist of numbness in the legs and feet, hyperesthesia, hyperpathia, with aching andburning pain. Not all patients have pain. Sensory symptoms consist of reduced or absent sensation to pain, touch,cold, heat, and vibration. Slowing in motor and sensory conduction is a common finding in diabetics and is attrib-uted to axonal degeneration with secondary demyelination. Autonomic neuropathy has recently been found to be animportant component of diabetic periperal neuropathy.

Alcoholic NeuropathyAlcoholic neuropathy is slowly progressive distal sensorimotor polyneuropathy. The disorder begins distally and

slowly spreads more proximally. Patients present with paresthesias, pain, and weakness. Foot drop, wrist drop, proxi-mal weakness with difficulty rising from a squatting position or chair may eventually be present. Plantar ulcers andcharcot foot-type disorders may occur. Alcoholic neuropathy only develops in cases of long-term alcohol abuse thatinvolves dietary deficiency.

Nutritional neuropathies (most frequently vitamin B12, but also other B vitamins, vitamin A, E, and folate) arecommon causes of peripheral neuropathy. Connective tissue disease is sometimes associated with peripheral neu-ropathy. However, negative antinuclear antibody testing and normal erythrocyte sedimentation tests rule out con-nective tissue disease as a cause of peripheral neuropathy. HIV neuropathy is a distal symmetric sensory polyneu-ropathy present in the late stages of HIV infection. Cancer can cause peripheral neuropathy and can be tested for byserum protein electrophoresis.

Any medication or drug potentially can cause peripheral neuropathy (See Table 4 on Page 119) for mnemonicand summary of peripheral neuropathies.

Table 4 . “DANG THERAPIST” Mnemonic for Causes of Peripheral nNeuropathiesMnemonic Name Description “D” Diabetic Polyneuropathy: sensorimotor in long-standing diabetes mellitus

Mononeuropathy: abrupt painful onset of 3rd or 6th cranial nerve palsieDiabetic amyotrophy (asymmetric lumbosacral plexus dysfunction)

“A” Alcoholic Sensorimotor neuropathy with multiple nutritional deficiencies “N” Nutritional Mostly B-complex vitamins-thiamin(B1, Niacin, B6, B12) “G” Guillain-Barre Acute form of inflammatory neuropathy; immunologically mediated,

chiefly motor, demyelinating, respiratory facial muscles may be involved,CSF protein often raised

“T” Toxic Drugs: furantoin, vincristine, cisplatin, isoniazid (vit B6 antagonism),penicillamine, gold salts, vit B6, Metals: lead (radial nerve palsies), arsenicIndustrial and environmental agents: acrylamide, hexacarbon solvents(industry, glue sniffing), triorthocresyl phosphate

“H” Hereditary Charcot-Marie Tooth disease: very slowly progressive, predominantlymotor, cavus foot, stork legs, often nerve enlargement dominantinheritance

“R” Recurrent Relapsing form of inflammatory neuropathy; often responds to steroids “A” Amyloidosis All forms include autonomic involvement“P” Porphyric Chiefly motor neuropathy, may progress rapidly; younger patients with

acute intermittent form of porphyria “I” Infection Diphtheria, leprosy“S” Systemic Association with collagen vascular diseases, uremia, sarcoidosis “T” Tumor Carcinomatous neuropathies; pure sensory or sensorimotor neuropathy,

may be combined with myoopathy (Adapted from BG Zier, Essentials of Internal Medicine in Clinical Podiatry, WB Saunders, Philadelphia, 1990.)


Muscular Dystrophies (MD)

MDs are a group of inherited noninflammatory muscle disorders resulting in weakness and secondary muscle

contracture. The four main types of muscular dystrophy are: (1) Sex-linked Duchenne’s pseudohypertrophic MD;

(2) Autosomal dominant fascioscapulohumeral MD; (3) Autosomal recessive limb-girdle MD; and (4) Myotonic

Muscular Dystrophy.

Duchenne’s MD occurs in 1 in 3500 live male births. Delayed milestones occur in infancy and early childhood

and the disorder may initially be confused with cerebral palsy. Since Duchenne’s MD is sex-linked, it is only found

in boys. The calf muscles appear large and firm because of fatty conversion (pseudohypertrophy). Manifestations

include delayed walking, waddling Trendelenburg gait. The patient cannot be lifted under the arms because of weak-

ness (Meryon’s sign) and the child “climbs up on himself” pushing his knee back to rise from a sitting position

(Gower’s Maneuver). There are no sensory deficits in muscular dystrophy. Progressive muscle weakness occurs in the

proximal muscle groups including the gluteus, quadriceps, abdominal muscles, and shoulder girdle muscles. Most

patients have cardiac involvement. Children become wheelchair bound and die usually by early adolescence from

pulmonary and cardiac failure. Becker’s MD is a benign form of sex-linked muscular dystrophy and occurs 1 in

30,000 live births. The onset is later than Duchenne’s MD (age 7) and the progression is slower. The genetic etiology

of both forms of sex-linked MD is due to an absence or mutation in the dystrophin gene found on the X-chromo-

some. The abnormal or absent dystrophin gene results in abnormal or absent dystrophin protein. Dystrophin pro-

tein is normally found in the cell membrane of muscle cells. Duchenne’s MD is caused by a complete absence of

dystrophin protein while Becker’s MD is caused by abnormal or insufficient amount of dystrophin protein.

Myotonic dystrophy is the most common inherited adult muscular dystrophy. It is interesting podiatrically since

it is the only muscular dystrophy affecting distal muscle groups and may present with foot drop.

ElectrodiagnosisIndications

Electrodiagnosis refers to nerve conduction velocity (NCV) testing and electromyography (EMG). Generally

both tests are done at the same time. It is the EMG that is somewhat painful. Patients should be referred for electro-

diagnosis for a problem that is presumed to arise from the neuromuscular system. Symptoms such as pain, weak-

ness, and numbness may be involved with lesions of the peripheral nerve. Electrodiagnosis is particularly useful in

localizing a lesion along the route of a peripheral nerve.

A major indication for NCV/EMG testing is to distinguish between demyelinating and axonal neuropathy.

These two conditions are clinically indistinguishable. Although EMG/NCV cannot determine the etiology of a spe-

cific peripheral neuropathy, by categorizing peripheral neuropathy into demyelinating and axonal neuropathy, and

correlating this with clinical symptoms and patient history, this narrows things down and aids with diagnosis.

Electrodiagnosis is also helpful in distinguishing a neuropathic (neurologic) process from a myopathic (muscle)

disease. Although neuropathy tends to affect the distal leg muscles resulting in foot drop and myopathy affects the

more proximal muscles resulting in weakness of the pelvic and pectoral girdle musculature, there is frequently great

clinical overlap. For example myotonic dystrophy is a muscle disease (adult muscular dystrophy) which affects distal

leg muscles resulting in foot drop. Guillain Barre Syndrome is a generalized neuropathy, which may result in paraly-

sis of the entire lower extremity (Table 5). Nerve conduction velocity testing can determine the exact location of a

nerve entrapment and can differentiate an entrapment from a diffuse neuropathy. Finally, electrodiagnosis can eval-

uate surgical intervention and can be used for medicolegal purposes.

See Table 5 on page 121 for a summary of indications for NCV/EMG.


Table 5. Indications for Electrodiagnostic Testing (NCV/EMG)Assessment of lesions of the peripheral nerve, e.g., peripheral neuropathyConfirm presence of sensory deficit in objective mannerDistinguish demyelinating neuropathy from axonal neuropathy. These two conditions are clini-cally indistinguishable and this indication is a common reason for patients being sent forEMG/NCV testing. Although EMG/NCV will not make the diagnosis of the specific peripheralneuropathy, by categorizing it into demyelinating or axonal neuropathy and correlating this withclinical symptoms and patient history, this narrows things down and aids with diagnosisDistinguish neuropathic (neurologic) process from a myopathic (muscle) disease. Although neu-ropathy tends to affect the distal leg muscles resulting in foot drop and myopathy affects the moreproximal muscles resulting in weakness of the pelvic and pectoral girdle musculature, there is fre-quently great clinical overlap. For example myotonic dystrophy is a muscle disease that affectsdistal leg muscles resulting in foot drop. Guillain Barre Syndrome is a generalized neuropathy,which may result in paralysis of the entire lower extremityEvaluate patients with acute ascending paralysis (Guillain Barre Syndrome) prior to beginningplasmaphoresisDetermine the anatomical location of a nerve entrapment Differentiate nerve entrapment from diffuse neuropathy Help to evaluate response to surgical intervention: Medicolegal

Figure 6. NCV Testing

Nerve Conduction Velocity Testing (NCV)

The nerve conduction velocity (NCV) test determines the rate with which a segment of the peripheral nerve

will conduct an impulse, and this is reported in meters per second. Nerve conduction velocity studies consist of the

stimulation of a peripheral sensory or motor nerve or a mixed nerve. A physiologic action potential (AP) is generat-

ed by electrical stimulation of the axon of the nerve. In a motor nerve, the AP of the corresponding muscle is

recorded. The action potential propagates down the axon where it is detected at a distant site by surface electrodes.

The latency time is the time between the stimulus and the response and the nerve conduction velocity is the speed

of impulse propagation. The amplitude tells how many muscle fibers are firing in a motor unit. Nerve conduction

studies evaluate the integrity of large myelinated sensory and motor neurons.

The NCV study has been likened to how fast a man can run. The EMG study has been likened to how much

arthritis he has.

Action PotentialThe NCV evaluates the action potential of peripheral sensory and motor nerves. Recall that the action potential

is an electrical disturbance passing down the axon of the anterior horn cell in the spinal cord to the myoneural junc-

tion where muscle is stimulated to contract. The action potential is self-propagating, nearly synchronous, and func-

tions in an all-or-none fashion. This property of the action potential of acting in a synchronous fashion is impor-

tant in pathologic EMG testing. Diseased nerves fire asynchronously and show up on EMG with polyphasic poten-

tials. The action potential measures the voltage change recorded from an excitable cell. Terms commonly found on


an NCV report include: CMAP, SNAP, and MUP. The CMAP is the Compound Muscle Action Potential and evalu-

ates the action potential of the entire muscle. The SNAP is the Sensory Nerve Action Potential, which evaluates the

action potential of a sensory nerve. The MUP refers to the Motor Unit Potential. This is the action potential of a sin-

gle motor unit.

The NCV test measures the distal latency, amplitude, and nerve conduction velocity of a peripheral motor, sen-

sory or mixed nerve. The distal latency is the time between stimulus of the nerve and the response and is generally

recorded in milliseconds. Normal values for nerves of the leg are in the range of 3-6 milliseconds. The amplitude

tells how many muscle fibers are firing in a motor unit and is recorded in millivolts. In the leg, very roughly 2.5 mil-

livolts is a typical normal value. The nerve conduction velocity is the speed of the nerve in meters per second and is

in the range of 40 to 60 meters per second. Generally nerve conduction velocities of the nerves to the upper extremi-

ty are faster (~50 meters per second) than nerves to the lower extremity muscles (~40 meters per second). The

fastest a nerve impulse can travel is about 80 meters per second. If you get back an NCV for a patient that reports

NCV values of significantly greater than this (i.e., 200 meters per second) this is impossible. Nerve conduction

velocity is one-half the adult normal value in the neonate and reaches its true normal value at about age 5 years.

Nerve conduction velocity declines after age 60. See Table 6 for a summary of Nerve Conduction Velocity Values.

Table 6. Nerve Conduction Velocity ValuesIndividual/Nerve/Condition Nerve Conduction Velocity Newborn 1/2 adult (28 m/sec) 3 year old Early adult value 5 year old True adult value reached >60 years NCV slows by 10 m/sec Cold Decreased NCV Nerves of Lower Extremity >40 meters/sec Nerves of Upper Extremity >50 meters/sec Beyond 3S.D. of mean Abnormal myelin Nonmyelinated nerves 7-10 m/sec Axonal neuropathies up to 30% below normal Polyneuropathies Slowed conduction in several especially distally Highest possible NCV 80 m/sec.Gender Faster in men than women Height Height and velocity are inversely proportional

The myelin surrounding a nerve is responsible for the speed of the nerve conduction velocity of the nerve.

Therefore large myelinated nerves have much higher velocities than unmyelinated nerves (7-10 meters per second).

For this same reason, nerve conduction velocities are markedly decreased in demyelinating neuropathies where the

nerve begins to lose its myelin.

Demyelinating diseases are characterized by severely decreased nerve conduction velocities, markedly prolonged

distal latencies, and normal (or only slightly decreased) amplitude (Table 7). In demyelinating neuropathy there is at

least a 60% reduction in nerve conduction velocity. Demyelination is directly responsible for reduced speed of the

nerve and may produce severe motor and sensory deficiencies. Clinically, demyelinating polyneuropathies have

greater motor impairment than sensory and little or no pain. Examples of demylinating neuropathies include

Charcot-Marie Tooth Disease Type 1A, Guillain Barre Syndrome, and peripheral neuropathy associated with cancer

(Table 7 on Page 123).


Table 7. Characteristics of Demyelinating and Axonal NeuropathiesNormal Values Demyelinating Neuropathy Axonal Neuropathy

Nerve conduction 40-60 m/sec. Greatly reduced Normal Distal latencies 3-6 msec Increased Normal Amplitude 2.5 mV Normal Reduced Examples CMT I CMT II

GBS Diabetic neuropathyToxinAlcoholNutritionalHIV

Axonal neuropathies are usually milder than demyelinating neuropathies and are characterized by spontaneous

activity in distal muscles with low amplitude evoked responses, with relatively normal conduction velocity (Table 6

on page 122. Conduction velocities are normal despite extensive axonal degeneration. This is because myelin is

responsible for the speed of the nerve impulse and the myelin remains intact in axonal neuropathies. Clinically,

axonal polyneuropathies are symmetrical and begin distally with subacute onset. Polyneuropathies due to axonal

degeneration are common and include diabetic neuropathy, alcoholic neuropathy, Charcot-Marie Tooth Disease

Type 2, and neuropathies caused by nutritional deficiency, connective tissue disease and toxins. Many neuropathies

are due to mixed axonal-demyelinating processes. Diabetes mellitus may also be associated with a mixed peripheral

neuropathy. Other mixed disorders include neuropathy associated with multiple myeloma or lymphoma, and several

drug-induced neuropathies.

Keep in mind that the NCV/EMG testing works best on large myelinated peripheral sensory and motor nerves.

For this reason patients with upper motor conditions such as stroke, cerebral palsy, multiple sclerosis, trauma to the

brain and spinal cord including herniated lumbar disc may be clinically paralyzed yet have normal NCV/EMG tests.

This is because the peripheral nerve system in these individuals is often normal.

In primary muscle disease (muscular dystrophy, myositis) the nerve conduction velocity will be normal, but the

EMG will be abnormal. Radiculopathies, because they involve the most proximal segment of the nerve, the nerve

root, may show a normal NCV test. The F wave and H reflex can be used to test for the presence of a radiculopathy.

Although the NCV may be normal in radiculopathy, the EMG test may show involvement of several muscles affect-

ed by the nerve root causing the radiculopathy. Anterior horn cell disease (Polio and Amyotrophic Lateral Sclerosis-

ALS) may have normal NCV’s, but changes will be most apparent on EMG. Peripheral nerve lesions if examined too

early may show a normal NCV.

Abnormal spontaneous activity (e.g., fibrillations) takes approximately two to four weeks to show up on EMG.

If a person claims nerve damage as a result of an accident or surgery and the changes are present on EMG one week

after the accident or surgery, the damage was probably present prior to the accident or surgery and is therefore not

the cause of the nerve damage. The fact that EMG abnormal spontaneous activity takes between two to four weeks

to show up on EMG can be used in legal cases if the patient claiming nerve damage is tested prior to two to four

weeks after the accident or surgery. If abnormal spontaneous activity is not present one week after the surgery/acci-

dent but becomes present two to four weeks after the accident or surgery, then the surgery/accident could be

responsible for the nerve damage. However, the patient could have had an intervening illness that is responsible for

the nerve damage.

The main contraindications for nerve conduction velocity are cardiac pacemaker and an indwelling cardiac

catheter.

F Response and H ReflexThe F response and H reflex evaluate conduction in the proximal portions of nerve fibers.


F Wave/F ResponseThe F wave is a compound muscle action potential that can be obtained from most muscles by supramaximal

electrical stimulation of the nerve. The F wave results from antidromic (opposite the normal direction of conduc-

tion) activation of the anterior horn cell motor neurons in the spinal cord, which then sends an impulse back down

the nerve orthodromically to stimulate the muscle. The F-wave latency provides information regarding the entire

length of the motor nerve from the anterior horn cell in the spinal cord to the muscle fibers it innervates. Thus, in

the case of a radiculopathy, for example, routine NCVs involving the below-knee segment may be normal, but the F

wave, as it traverses the proximal, abnormal nerve segment, may be delayed.

The F response was named because it was first observed in small foot muscles. It is a measure of conduction

along the entire length of nerve from the distal point of stimulation to the anterior horn cells and back to the distal

recording electrode. Normal values depend on limb length but are usually less than 32 msec in the arms and less

than 60 msec in the leg. When the F-response latency is prolonged and distal velocity is normal, slowing occurs in

the proximal segment. This pattern is seen in polyradiculopathies and Guillain Barre syndrome. In chronic demyeli-

nating neuropathies, the proximal segments may also be involved and the F response latency may be prolonged.

H ReflexThe H reflex is considered to be the electrical counterpart of the Achilles reflex. The H reflex is normally found

only in the tibial nerve/soleus system or in the median nerve/flexor carpi radialis system. It is one of the few meas-

ures of afferent nerve conduction in the proximal portion of sensory nerves and identifies dorsal root pathology

when the H reflex is prolonged in conjunction with normal F response latency in the same nerve.

A delayed response, in the face of normal NCSs, indicates proximal, usually nerve root disease. The H reflex

may indicate upper motor neuron diseases, such as multiple sclerosis.

Electromyography

Electromyography is the study of spontaneous and voluntary electrical wave forms generated in the motor unit

and recorded from muscle fibers. The EMG shows the wave form. It is actually the measurement and observation of

action potentials caused by depolarization and repolarization of a muscle fiber as a result of injury of an electrode

needle.

In the EMG study a needle is actually inserted into the muscle belly which can be fairly painful. There are four

parts to the EMG study which begins after insertion of the needle.

• Insertional Activity. This is as the needle is being inserted. This is painful and there should be some sponta-

neous muscle activity recorded. In fact, absence of insertional activity indicates no functioning muscle

fibers or that the electrode was inserted incorrectly and is not in the muscle tissue

• Muscle at rest. The muscle at rest is electrically silent. Spontaneous activity of any type is abnormal

• The patient is asked to just think of contracting the muscles. There should be some interference on the

screen noted at this point

• The patient is asked to actively contract the muscle. At this point there should be full electrical activity with

what is known as a full interference pattern


The diagnostic information provided by the EMG test includes:

• The nature of the motor wave form, e.g., amplitude, number of phases, duration of the wave

• It analyzes the recruitment pattern, the density of motor units during maximal activation (firing rate, fre-

quency)

• Tells the type and amount of abnormal spontaneous activity (Table 8). After denervation, muscle fibers fire

spontaneously. Spontaneous activity is always abnormal and includes fibrillations, fasciculations, and positive

sharp waves.

The amplitude is a measure of the height of the evoked potential. The amplitude approximates how many mus-

cle fibers are in a motor unit. The amplitude is diminished in muscle disease where there is a loss of muscle fibers.

However, the amplitude is usually increased in neuropathic disease due to reinnervation because a given axon will

innervate a greater number of muscle fibers resulting in giant motor units and subsequently a very high amplitude.

The phase is that part of the motor unit potential that lies between two crossings of the baseline. There should

be between two to four phases in the normal action potential. A potential with more than four phases is termed a

polyphasic motor unit potential. Normal skeletal muscle recordings may contain up to 12% polyphasic motor unit

potentials. The phase depends upon the maturity of the neuron branches to various muscle fibers and increases dra-

matically during reinneration by collateral sprouting, but decreases as new sprouts mature and exhibit more rapid

conduction. In other words at the beginning of reinnervation, motor unit action potentials are characteristically

polyphasic. In fact, polyphasic motor potentials (formerly called nascent potentials) heralds the beginning of rein-

nervation of denervated muscle and is a happy sign for patient and physician.

Interference Pattern

When a muscle contracts, the cumulative electrical activity of all the motor units firing is referred to as the

interference pattern. A full interference pattern fills the oscilloscope screen during normal muscle contraction. In

neurogenic disorders, axons degenerate, the number of motor units in an individual nerve falls, and the result is an

incomplete, or decreased, interference pattern.

Recruitment Pattern

Recruitment pattern refers to the electrical activity generated by all activated motor units within the recording

area of a maximally contracting muscle. The recruitment evaluates the frequency of firing of the motor unit.

Recruitment may be normal, neuropathic, or myopathic. The recruitment pattern on maximal effort normally

should be dense with no peaks in the baseline with an amplitude of 2 to 4 mVolts. In myopathic recruitment, there

is a full or increased recruitment with weak contraction. There is early recruitment. Many units are recruited with

low level of recruitment in myopathy. A full interference pattern with small amplitude is pathogneumonic for myo-

pathic recruitment. In neuropathic recruitment there is a reduced number of motor units therefore fewer motor

units can be recruited, but those that are recruited are large units with many muscle fibers (high amplitude) long

duration, and polyphasic. These are signs of chronic denervation.


Table 8. Information from Electromyography• Nature of the Wave form

– Amplitude– Phasicity– Duration

• Abnormal Spontaneous Activity • Recruitment Pattern

Insertional Activity

Muscles at rest are electrically silent. The small tension referred to as muscle tone has no EMG equivalent.

Insertional activity occurs from activation of muscle fibers with mechanical stimulation of electrode movement.

Insertion of the needle electrode into the muscle injures and mechanically stimulates many fibers causing a burst of

potentials of short duration (normal insertional activity). Insertional activity is normal. Absence of insertional activ-

ity indicates NO FUNCTIONING MUSCLE FIBERS or that the electrode is not in muscle tissue. Increased inser-

tional activity is a feature of myopathic disorders. Normal spontaneous activity during insertion includes end-plate

noise generally associated with painful needle placement and end-plate spikes. With slight movement of the elec-

trode, end-plate noise and spike should disappear. It is important not to confuse end-plate spikes and end-plate

noise with fibrillation potentials.

Spontaneous Activity

This consists of several kinds of abnormal potentials, the most common being fibrillations, positive sharp

waves, and fasciculations. There should be no spontaneous activity. Spontaneous activity is never normal except for

brief periods during electrode insertion into the muscle as described above. However, 10% or greater of normal peo-

ple have positive spontaneous muscle activity in the pedal musculature as a result of the trauma inflicted by daily

activities.

Minimal to moderate Muscle Contraction. The patient is asked to just think about contracting the muscle.

Amplitude is 200-2000 mV; duration is 4-12 msecs. The wave form is diphasic or triphasic. Minimal to moderate

muscle contraction is good for demonstrating recruitment. Recruitment initially is by the smaller motor units most

easily recruited.

Maximal Muscle Contraction. The patient contracts the muscle against maximal resistance to the examiner. The

amplitude is 200-2000 mV. Recruitment of larger, previously inactive motor units occurs with complete interference

pattern.

Abnormal EMG FindingsFibrillation Potentials

Fibrillation potentials are single muscle fiber action potentials caused by muscle membrane instability. The

muscle membrane instability is caused by denervation. Fibrillation potentials are caused by depolarization of single

muscle fibers.

Fibrillation potentials are the single most significant diagnostic finding of nerve damage. They are not visible

under the skin. These spontaneous potentials appear three to four weeks after nerve injury.

Fibrillation potentials initially appear in muscles just distal to the lesion. In complete lesions they will disappear

after one year signaling death and complete fibrosis of the muscle. With incomplete lesions, they will persist for

years. Fibrillation potentials are always abnormal and indicate denervation or myopathy. They are frequently present

in lower motor neuron disease. One of the best signs of reinnervation is that fibrillations stop.

Fibrillation Potential are graded from 1–4 (Table 9 on Page 127).

• Grade 1 fibrillation potentials are difficult to find on the screen, present only when muscle is stimulated

mechanically. Persistent activity must be present in at least two muscle regions

• Grade 2 fibrillation potentials consist of a few fibrillations without mechanical stimulation. Moderate activity

must be present in three or more muscle regions to have a grade 2

• Grade 3 fibrillation potentials consist of abundant activity in all muscle regions tested

• Grade 4 fibrillation potentials the oscilloscope screen is filled with fibrillation potentials


Table 9. Grading of Fibrillation PotentialsGrade 1 Difficult to find, present only when muscle stimulated mechanically. Persistent activity

in at least two muscle regions.Grade 2 A few fibrillations without mechanical stimulation. Moderate activity in three or more

muscle regions.Grade 3 Abundant activity in all muscle regions tested.Grade 4 Oscilloscope screen filled with fibrillation potentials.

It is possible to miss fibrillations on EMG for the following reasons:

• Not waiting 2-4 weeks after the injury, doing the EMG too early after the injury;

• The damage may be too mild to cause denervation and fibrillations should not be present;

• Temperature of the muscle is too low secondary to circulatory problems;

• Muscle fiber may be totally inactive due to severe atrophy—after a year fibrillation potentials will cease in

complete lesions;

• Reinnervation—The best sign of reinnervation is fibrillation stops.

Positive Sharp Waves

The second type of abnormal spontaneous activity is positive sharp waves (PSW’s). Positive sharp waves consist

of abnormal insertional activity. These appear 8-16 days after nerve injury upon the insertion of the electrode.

Positive sharp waves are single motor fiber action potentials. They are similar to fibrillation potentials, but appear

earlier than fibrillation. Positive sharp waves may indicate denervation or myopathy.

Fasciculation Potentials

Fasciculations are commonly known as muscle twitches and can be seen through the skin in contrast with fib-

rillations. Fasciculation potentials are spontaneous discharges of an entire motor unit or part of a motor unit that

comprise all the muscle fibers innervated by a single axon. Seventy percent of normal individuals admit to muscle

twitch at periods in their life. Fasciculation potentials are evidence of motor nerve fiber irritability and not of nerve

fiber destruction and motor unit denervation. Occasional fasciculation potentials—particularly in the calves, hands,

periocular or paranasal muscles occur in many normal persons. They can last for days or even years in some indi-

viduals, without weakness or wasting (benign fasciculations). Shivering induced by low temperature and twitching

associated with low serum calcium levels is a form of fasciculatory activity. Fasciculation potentials occur with great

frequency in chronic, slowly advancing, destructive diseases of the anterior horn cells such as ALS and progressive

spinal muscular atrophy, in the early stages of polio. Fasciculations are thought to return in post-polio syndrome.

Fasciculations are associated with proximal diseases such as anterior horn cell disease or radiculopathy. They are less

common in peripheral neuropathy.

Polyphasic Potentials

Polyphasic potentials are motor unit action potentials having more than three or four phases. Polyphasic poten-

tials represent asynchronous firing of muscle fibers. They are a sign of damage to muscle fibers. Fewer than 10% of

motor unit action potentials in normal individuals are polyphasic. Polyphasic potentials are caused by differences in

conduction times over terminal axon branches. Multiple motor units do not fire simultaneously.

Polyphasic potentials were formerly called nascent potentials, consisting of low amplitude short duration poten-

tials. Polyphasic potentials appear two-eight months after paralysis in peroneal nerve palsy and are the first sign of

recovery.

They are a good sign, appearing two months before return of muscle function. They herald reinnervation of

denervated muscle.


Nascent Potentials

Nascent potentials are reinnervation potentials. They are highly polyphasic, low amplitude, short duration and

appear early in reinnervation.

Giant Potentials

Giant potentials are voluntary motor unit action potentials. Giant potentials are high amplitude, long duration,

and polyphasic.

Neurogenic recruitment consists of giant action potentials. Selective destruction of small motor units occur;

large motor units remain due to axon sprouting anterior horn cells. Polio and ALS are diseases that characteristically

have giant action potentials.

Motor Unit Potentials In Denervation

In neurogenic disease, the motor unit increases in duration and amplitude. Denervated muscle fibers are even-

tually reinnervated by sprouts of nearby surviving axons. Since the number of muscle fibers innervated by each sur-

viving motor axon is increased, the AMPLITUDE of the reconstituted motor unit potential is greater than normal.

The new connections are often not activated synchronously with the original connection so motor unit potentials

are usually POLYPHASIC and INCREASED IN DURATION. In early reinnervation the muscle unit potential will be

low in amplitude, extremely prolonged duration, and polyphasic. In late reinnervation, (Chronic reinnervation), the

amplitude is high as reinnervation continues. Duration is not prolonged.

Recruitment Patterns In Neuropathic Disease

Recruitment patterns in neuropathic disease are reduced because the number of motor units is reduced. If a

muscle is weakened by denervation, there will be fewer motor unit potentials (MUPs), firing at a moderately rapid

rate (reduced recruitment). The characteristic neuropathic motor unit potentials are: High amplitude, long dura-

tion, with polyphasic potentials. Polyphasic potentials are the hallmark of chronic denervation and signal

reinnervation.

In myogenic disease, motor unit potentials decrease in amplitude and duration. Myopathic motor unit poten-

tials are characteristically brief short duration, small amplitude polyphasic potentials. Duration is not prolonged.

Recruitment pattern is full (increased recruitment) with relatively weak contraction. There is early recruitment with

many units recruited at abnormally low level of effort in myopathy. Full recruitment in a weak, wasted muscle is a

pathognomonic finding of myopathy.

Myotonic Discharges

True myotonia is the EMG correlate of the clinical phenomenon of impaired relaxation of a voluntarily induced

contraction of a muscle. Myotonic discharges are present only in Myotonic Dystrophy.

Myotonic discharges correspond to clinical failure of voluntary relaxation of muscle after forceful contraction.

It consists of a high-frequency repetitive discharge, with a waxing and waning of amplitude and frequency produc-

ing the well-known “dive-bomber” sound, the most distinctive sound in EMG. Myotonic discharges are most promi-

nent in the intrinsic hand muscles.

Myokymia

Myokymia consists of persistent involuntary irregular quivering and rippling of muscles at rest. Myokymia

consists of bursts of motor unit activity induced by abnormal excitation. Myokymia is most common in periorbital

or other facial musculature. Myokymia does not stop in sleep but is abolished by xylocaine block of the nerve inner-

vating the muscle. Myokymia occurs in demyelinating polyneuropathies, i.e., Guillain Barre syndrome, multiple

sclerosis.


Signal Comparisons

Figure 7 shows comparison of neuropathic and myopathic recruitment with normal recruitment. Notice in nor-

mal recruitment there is full interference. In neuropathic recruitment there is reduced interference, but high ampli-

tudes of functioning motor units. In myopathic recruitment there is full interference with reduced amplitude.

Figure 7. Signal Comparisons


Documents

Chapter 3c Neuromuscular Disease and Electrodiagnosis