Early onset cerebellar ataxia with retained tendon reflexes (EOCA): an electromyographic study.

This prospective study was undertaken to characterize better electrophysiologically the newly described clinical entity of "Early onset cerebellar ataxia with retained tendon reflexes (EOCA)" and compare it with Olivopontocerebellar atrophy (OPCA) and Friedreich's ataxia (FA). Concentric needle electromyography and motor (median, common peroneal and posterior tibial) and sensory (median, sural and posterior tibial) nerve conduction studies were carried out in 14 patients of EOCA. The results were compared with those of 10 and 16 patients of FA and OPCA respectively. All patients of EOCA had either motor or sensory conduction abnormalities, motor being slightly more frequent than sensory (87.7% versus 78.6%). The neuropathy was distal and symmetrical, lacked correlation with duration or clinical stage of the disease, even between patients of the same family. Electrophysiological studies helped to detect subclinical motor and sensory neuropathy in most of the patients. No characteristic electrophysiologic abnormalities separated patients of EOCA from those of OPCA or FA, though the overall incidence of abnormalities was higher in the latter two groups. It is concluded that subclinical peripheral neuropathy is often present in patients of EOCA. The impaired proprioceptive sensation noted among these patients may be due to large fiber neuropathy rather than posterior column involvement alone. A subgroup of them, who have severe sensory neuropathy, may be difficult to differentiate clinically from patients of FA. The clinical entity of EOCA is indistinguishable electrophysiologically from FA and OPCA.