A family with autosomal dominant hereditary myokymia and paroxysmal ataxia, linked to chromosome 12p, is described from University Hospital Groningen, The Netherlands. The proband, a 20 year old woman, had an onset of attacks of ‘swinging legs’, dizziness, involuntary jerky limb movements, dysarthria, and gait ataxia beginning at 6 years of age. Attacks up to four times daily and lasting 10 seconds to 5 min occurred at rest, during exercise, or when startled, standing up, or running. Myokymia of the hands and semirhythmical movements of fingers were noted on examination, and EMG showed myokymic discharges. An attack provoked by knee bends consisted of rhythmic involuntary shaking of limbs, and tremor and dysmetria on finger-to-nose test. Acetazolamide prevented attacks, but treatment was limited by paraesthesiae and development of tolerance. A 22 year old brother was also affected from 6 years of age, and the myokymia and ataxia were complicated by paroxysmal kinesigenic dystonia at 15 years, after a mild head injury. Another family member also had attacks of paroxysmal choreoathetosis. Carbamazepine controlled the attacks of dystonia and choreoathetosis but not the ataxia. Data on 6 affected family members are tabulated. 
COMMENT. Provisional diagnoses of basilar migraine and epilepsy had been made initially in two of three children with familial paroxysmal ataxia reported in the UK (Hawkes CH, 1992). The EEG was normal and the MRI showed atrophy of the superior cerebellar vermis. All responded to acetazolamide. (see Progress in Pediatric Neurology II, PNB Publ, 1994, pl49-150). MRI findings were not reported in the above series. An overlap and relation between paroxysmal types of ataxia, myokymia, choreoathetosis and dystonia is strengthened by this report, although different responses to acetazolamide and carbamazepine may suggest separate etiologies.