Electromyography

• Nerve conduction study (NCS)

• Electromyography (EMG)

• Evoked potential study (EP)

Abnormal Wave

Latency (msec)

Amplitude

(uV)-

+

Decreased amplitude:axonal/neuronal damage ;axono-/neuronopathy

Prolonged latency, decreased velocity:myeline damage;demyelination

AB

C

Nerve Conduction Study

• Motor NCS

• Sensory NCS

• Reflex study– F-wave– H-reflex– Blink reflex

• Repetitive nerve stimulation study

Electromyography

• Needle EMG– Conventional needle EMG– Quantitative EMG– Single Fiber EMG

• Surface EMG

Mortor NCS

Axonal degeneration vs Demyelination

• Charater Axonal Demyelinating

NCV N Amplitude N or CB

Duration N Dispersion()F-latency

F-wave, H-reflex

Blink reflex

RNS

Electromyography

• Insertional activity

• Spontaneous activity– Positive sharp wave– Fibrillation potential– Fasciculation

• Motor unit potential

• Recruitment

•Amplitude•Duration•Phase

Neuropathy vs Myopathy

• CharacterNeuropathy Myopathy

IA SPA (+) (+)(-)

MUP amp duration phase

Recruitment

- Peripheral neuropathy: DM, Entrapment neuropathy, Radiculopathy, Guillain-Barre syndrome (AIDP), CIDP

- Motor neuron disease: ALS, PLS

- Myopathy: inflammaotory polymyositis, dermatomyositis

- Neuromuscular junction disoder (Myasthenia gravis, Lambert-Eaton syndromes): Repetitive nerve stimulation test (Jolly test) - Autonomic function test and sphincter EMG: MSA vs. IPD

- Blink reflex and facial NCS: Bell’s palsy, Trigeminal neuralgia, Blephalospasm  

Clinical utility of EMG and NCS