Myoclonus epilepsy in two brothers. Clinical features and neuropathology of a unique syndrome.

We report 2 brothers with progressive ataxia, seizures, myoclonus, supranuclear ophthalmoplegia, progressive visual loss and embolic strokes. The epilepsy and myoclonus came on many years after the onset of the ataxia. In the more severely affected brother the myoclonus was often unilateral and focal but ultimately involved both sides of the body. His sibling had only unilateral myoclonus after a contralateral middle cerebral artery stroke. When focal, persistent and unilateral, the myoclonus in both brothers was clinically similar to epilepsia partialis continua except that muscles of the trunk and proximal limbs were the most affected. It was exacerbated by movement of the affected part but was otherwise not stimulus sensitive. The more severely affected brother had a pigmentary retinopathy and a cardiac fibromyxoid valvulopathy. In his sibling, visual loss was not fully investigated and the heart was not examined at autopsy though he had a longstanding heart murmur. Neuropathological studies showed pancerebellar cortical atrophy, cell loss in the inferior olivary nuclei and old right middle cerebral artery infarctions in both brothers. Biochemical assays for known metabolic diseases were negative. We suggest that this syndrome represents a unique autosomal recessive form of progressive myoclonus epilepsy of unclear aetiology. It is distinguished from other familial myoclonus epilepsies by the presence of early onset cerebellar ataxia, supranuclear ophthalmoplegia, pigmentary retinopathy and possibly cardiac valvulopathy with subsequent cerebral emboli.