[A case of Isaac's syndrome--continuous muscle fiber activity syndrome]

A 34-year-old woman noted difficulty of gait initiation, then dilated finger opening and hyperhidrosis appeared. Her stature was a muscular habitus, and muscle stiffness and myokymia were found in all muscles of the extremities. Her stiffness persisted during sleep. Her calf muscles were large and a contracture was noticed in ankle joints. There was no evidence of wasting and weakness. A remarkable delay in voluntary relaxation of the contracted muscles without percussion myotonia was recognized. Tendon reflexes of lower extremities were absent. Laboratory examination revealed elevation of CPK, LDH, myoglobulin, aldolase and basal metabolic rate (BMR). An extraband of CPK isoenzyme between MB and MM fraction was observed. The thin layer gel filtration technique and immunofixation technique showed that this extraband was complexes of CPK and IgA, and light chain of the CPK linked IgA was lambda type. All other laboratory tests were normal for the following: urinalysis, ESR, a blood count, liver function, kidney function, glucose, rheumatoid factor, CRP, thyroid function, parathyroid function, serum electrolytes, ECG, EEG, cranial CT, without slight elevation of IgA, and CSF protein. In needle EMG and surface EMG spontaneous discharges were recorded at rest. These discharges consist of normal motor unit potentials, doublets, and triplets in needle EMG. The discharges were markedly reduced after the median nerve block with xylocaine. In needle EMG, myotonic discharge was not observed. Nerve conduction velocities were within normal ranges. According to these data, she was diagnosed as having Issacs' syndrome (continuous muscle fiber activity syndrome). Carbamazepine, 200 mg daily was administrated and showed a dramatic reversal of the symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)