Peroneal muscular atrophy with ataxia and partial myoclonic epilepsy.

Two brothers, 17 and 11 years old, presented with pes cavus, absence of deep tendon reflexes, péripheral vibratory sensory loss, ataxia, tremor, nystagmus, dysarthria and partial myoclonic epilepsy. Electromyography showed severe slowing of motor conduction velocity in the lower extremities and increased distal latencies. A peroneal nerve biopsy showed absence of myelin sheath in most fibres resulting in numerous demyelinated nerve fibres. The father and seven uncles on the paternal side had pes cavus, hammer toes and moderate vibratory peripheral sensory loss. Three of seven siblings had slow motor conduction velocities on EMG. None had EEG abnormalities. Epilepsy started at an early age in both patients with myoclonic jerks of the right arm especially during sleep. EEG recordings were characterized by focal or diffuse epileptiform discharges. In the elder brother a partial motor epileptic status occurred with adversive seizures involving the right side of the body. He died of a broncopneumonia after 3 days of this epileptic status. Histopathological examination showed a severe demyelination of dentato-rubral pathways in the cerebellum and a partial degeneration of Goll and Burdach's tracts in the cervical spinal cord. The nosological classification of this syndrome is discussed and an autosomal dominant inheritance with incomplete penetrance or variable expressivity is suggested.