Nationwide survey in Japan endorsed diagnostic criteria of benign adult familial myoclonus epilepsy.

Purpose: Benign adult familial myoclonus epilepsy (BAFME) is an autosomal dominant disease representing tremulous myoclonus or cortical tremor and infrequent generalized seizures. We aimed to delineate detailed epidemiological backgrounds in patients with Japanese BAFME and to establish diagnostic criteria based on clinical and electrophysiological findings.

Methods: After a previous survey on the current nationwide state of myoclonus epilepsy of adults in Japan, we conducted this survey to delineate the clinical characteristics of Japanese BAFME patients, using a questionnaire to obtain details for individual patients. Based on clinical diagnostic criteria, we analyzed demographic and clinical characteristics of 101 BAFME patients in 74 families.

Results: BAFME patients were predominantly female and were widely distributed throughout Japan. Ninety-two patients (91.1%) showed signs of cortical tremor and 84 (83.2%) showed epileptic seizures. Epileptic seizures were infrequent in BAFME patients, but 22.6% of patients had more than one seizure per year at the maximum. Three patients (3.0%) showed cerebellar ataxia, eight (7.9%) showed cognitive impairment, and 13 (12.9%) had psychiatric symptoms. Brain MRI was normal in 74% of patients, and the remaining patients had non-specific abnormal findings. Sodium valproate and clonazepam were the primary drugs used for BAFME patients. The older patients showed significantly more severe and higher rates of abnormal electrophysiological results, which were suggestive of cortical hyperexcitability.

Conclusion: Our study successfully delineated the overall clinical characteristics of Japanese BAFME. The correlation between the genetic, clinical, and electrophysiological results will be very important to further elucidate the pathophysiology and treatment of BAFME in the future.