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Idiopathic Generalized Myokymia (Isaacs’ Syndrome) with Hand PosturiG

Resembling Dystonia

Isaacs’ syndrome (IS) is a rare disorder due to an un- defined hyperexcitability of peripheral motor nerves characterized by the presence of diffuse myokymia (con- tinuous irregular discharges from motor units) (1-3). Stiff- ness, myotonia, and other features may be present. Ab- normal hand and wrist posturing that might be confused with dystonia has also been described (43). We present an IS patient with videotape documentation of this “dys- tonic” hand posturing.

Case Report

A 21 -year-old woman developed involuntary “twitch- ing” of her leg muscles at 7 years of age. Soon thereafter she developed involvement of her tongue, face, and upper limbs. When severe the muscle twitching often resulted in painful intermittent or sustained limb movements. In par- ticular, she noticed that her wrists and sometimes her feet spontaneously would develop a sustained posture, i.e., wrist flexion and foot inversion with plantar flexion. This posturing occurred while supine and at rest or while standing or sitting, and interfered with her ability to per- form fine motor tasks such as writing. Her foot posturing was uncommon and never affected her gait or caused a fall. She denied weakness, stiffness, altered sweating, or problems relaxing her grip. There was no worsening in cold weather. Her ability to exercise was limited by early fatigability, and she had never experienced darkening of her urine. Her past history revealed that she had a seizure at birth, and she subsequently had febrile seizures asso- ciated with throat infections. She had no further seizures after undergoing a tonsillectomy at 2 years of age. The patient’s sister also had a seizure disorder. The family history was negative for muscle or nerve problems.

General examination revealed coarse facial fea- tures with acne. Widespread myokymia was pre- sent, and the video demonstrates involvement of the or- bicularis oculi, orbicularis oris, quadriceps, hip adduc- tors, and the abductor digiti minimi muscles. Posturing resembling dystonia was evident in both hands at rest, consisting of sustained wrist flexion, flexion of the fingers at the MCP joints, and extension at the interphalangeal joints. Cranial nerves and the remainder of her motor examination were normal. Her Achilles reflexes were ab- sent, and all other reflexes were normal, including bilat- eral plantar responses. Her coordination, sensory func- tion, and gait were normal. Chvostek’s sign was absent.

Motor nerve conduction studies of the right median and right peroneal nerves were normal, as were sensory stud- ies of the right median and right sural nerves. Needle examination of the right quadriceps and extensor digito- rum communis muscles demonstrated increased inser-

tional activity and multiplets at rest. Normal motor unit potentials and recruitment pattern occurred with volun- tary contraction.

Initial treatment with 200 mg/day of phenytoin was par- tially effective, and carbamazepine 1,000 rng/day was added for additional benefit but resulted in little improve- ment. However if she did not take her medication the posturing would become persistent and intolerable due to pain. She underwent a 3-day course of intravenous gam- maglobulin without benefit. A recent course of plasma- pheresis improved her symptoms, and the effect has been maintained to date, now 2 months later.

Discussion

Our patient illustrates some of the characteristic fea- tures of IS. This includes the presence of generalized my- okymia with associated electromyographic evidence (see videotape) of irregular bursts of single motor unit dis- charges occurring at a high frequency (I). Fasciculation and fibrillation potentials may also be seen; however they were not present in the muscles studied in our patient.

Our case provides additional documentation of hand posturing in IS and is the first videotape demonstration of this feature. Isaacs demonstrated that this posture was associated with EMG activity in the extensor and flexor compartments of the forearm (presumably synchronous) and thereby similar to the agonist-antagonist co- contraction that is seen in dystonia (4).

The occurrence of dystonia due to peripheral causes is rare, and we recommend including IS in this short list as it is presumed to be due to peripheral motor nerve dys- function possibly from an immunologically mediated dis- turbance of potassium channels (1).

Legend to the Videotape

The first segment depicts sustained bilateral wrist flex- ion while the patient is supine and at rest. This hand posturing is accompanied by a quivering, jerky motion due to underlying myokymia involving various muscles of the hands and forearms, especially in the right abductor digiti minimi as seen on a close-up view. Myokymia is also seen in the orbicularis oculi, orbicularis oris, quad- riceps, and hip abductor muscles at a time that the patient was off medication for 24 h. This is followed by an EMG demonstration of multiplets in the right quadriceps mus- cle at rest. The last segment shows diminished but per- sistent myokymia while the patient is taking 700 mg of carbamazepine and 200 mg of phenytoin.

Paul J. Tuite Carlos Navarette

Vera Bril Anthony E. Lang

Division of Neurology Toronto Hospital

Toronto, Ontario, Canada

Movement Disorders, Vol. 11, No. 4, 1996

COMMUNICATIONS 449

References 1. Newsom-Davis J, Mills KR. Immunological associations of

acquired neuromyotonia (Isaacs’ syndrome). Brain 1993; 116:453-469.

2. Jamieson PW, Katirji MB. Idiopathic generalized myokmia. Muscle Nerve 1994;17:42-51.

3 . Isaacs H. A syndrome of continuous muscle-fibre activity. J Neurol Neurorurg Psychiatry 1961 ;24:319-325.

4. Isaacs H. Continuous muscle fibre activity in an Indian male with additional evidence of terminal motor fibre abnormal- ity. J Neurol 1Veurosurg Psychiatry 1967;30: 126-133.

5. Wallis WE, Poznak AV, Plum F. Generalized muscular stiff- ness, fasciculations, and myokymia of peripheral nerve ori- gin. Arch Neurol 1970;22:43&439.

A Neuromyotonic Process in a Transposed Latissimus Dorsi Muscle Stemming from

Radiotherapy and Peripheral Surgery

Neuromyotonia is a syndrome of peripheral nerve origin, characterised by signs of motor nerve hyperactivity, such as myokymia, fasciculations, muscle stiffness, and cramps, which can be triggered by voluntary or induced muscle con- traction (1). Neuromyotonia may arise in the context of he- reditary neuropathies (2); postirradiation therapy (3); immu- nological disorders, such as thymoma and myasthenia gravis (1); or malignancy (4). We describe one case occur- ring after radiation therapy, but confined to a latissimus dorsi muscle, which had been surgically transposed as part of a previous cosmetic surgical operation.

Case Report

A 48-year-old woman underwent a left-sided partial mastectomy in 1984 for carcinoma of the left breast. She subsequently received a total dose of 64 Gy of radiother- apy over 6 weeks to the area of the left breast, the left axilla, and the left supraclavicular region, following which she experienced Lhermitte’s phenomenon in both arms. The latter subsided over weeks, only to be replaced by a shooting dysaesthesia on the medial aspect of the left forearm triggered by pressure on the left supraclavicular fossa. In 1986 she elected to receive a silicone cosmetic implant in the remaining area of the left breast, but it was complicated almost immediately by infection and encap- sulation and was removed. In 1990 she received another smaller prosthesis combined with the transposition of the left latissimus dorsi insertion tendon onto the anterior chest wall to form a muscular flap. The second prosthesis again encapsulated and was removed. A new implant was inserted under the flap in 1991.

Eight months later, she noticed painless twitches in the region of the transposed muscle associated with a con- stant dysaesthesia in the left medial forearm, left index finger, and thumb. The twitching initially appeared on exercise of the left hand, such as typing, but over the next year became spontaneous, only subsiding on lying flat, perfectly still, or during sleep. By 1993, at the age of 58,

it was preventing her from performing her secretarial du- ties, and she was referred to the National Hospital for Neurology and Neurosurgery. She was otherwise system- ically well, did not take regular medication, and had never taken neuroleptic medication. Neither she nor her family had a history of neurological disease.

Systemic examination was within normal limits. She had a left mastectomy scar, and the latissimus dorsi flap was seen to jerk irregularly, each jerk lasting roughly 1 s. Observation from the front and back suggested that the jerking was restricted to the transposed muscle (see vid- eotape segment). The frequency and amplitude of the jerking was increased by opening and closing the left hand, but recruitment of other muscles was not wit- nessed. When asked to relax completely, lying on a bed, the movement ceased intermittently for a few seconds. In the left arm, shoulder abduction and adduction, elbow extension, wrist extension, and function of the small mus- cles of the hand were minimally weak. The left triceps reflex was reduced compared with the right. There was dysaesthesia to light touch on the left medial border of the forearm from the elbow to the little finger and loss of pin-prick sensation in the left thumb. Jerking could not be increased by somatosensory stimuli, noise, or pressure in the left supraclavicular fossa. The rest of the neurological examination was normal.

Results of the full blood count, erythrocyte sedimenta- tion rate, serum electrolytes, liver function tests, and bone biochemistry were normal. Syphilis serology was negative. Chest radiography found marked left-upper- lobe lung fibrosis. Sensory nerve action potentials (SNAPS) were of reduced amplitude in the left median nerve (F2-wrist measured 4 pV) and left radial nerve (30 FV), but they were of normal amplitude in the left ulnar nerve (10 pV) and left medial cutaneous nerve of the forearm (15 pV). All sensory and motor conduction ve- locities were normal.

Electromyography (EMG) of the left biceps, brachio- radialis, flexor carpi radialis, flexor carpi ulnaris, and ex- tensor digitorum communis found no spontaneous activ- ity, a mild excess of polyphasia with some increased du- ration and fast firing of motor units, and a slightly reduced interference pattern. EMG of the transposed left latissi- mus dorsi showed virtually continuous spontaneous elec- trical activity coinciding with multifocal muscle contrac- tions. A variety of patterns were seen, including myo- kymia, complex repetitive discharges, neurotonic discharges (60-100 Hz), fasciculations (occasionally re- petitive, polyphasic, and of long duration), and bursts (1-2 s ) of fast-firing (30 Hz), long-duration, polyphasic (1 mV) motor units. A voluntary interference pattern could not be obtained, but coughing produced a burst of long- duration, polyphasic motor units.

Somatosensory evoked potentials (SSEP) of the me- dian nerves revealed a normal latency but significantly attenuated N9 potential on the left (2.4 microvolts) as compared to the right (8.1 microvolts). The Nl1 latencies were bilaterally normal. There was a relative delay of the left N13 (cervical cord) and N20 (cortical) potentials by 1.1 and 0.8 milliseconds respectively, as compared with the right. SSEP from the ulnar nerves were within normal limits bilaterally.

Movement Disorders, Val. 11, No. 4 , 1996