[Electromyographic analysis on juvenile muscular atrophy of unilateral upper extremity (author's transl)]

In 1959, this disorder was first reported by one of authors (K.H.) (6). Since then, many Japanese cases have been reported and recently some cases are also reported in other countries. Its cause and pathology are still unknown, because no autopsy case was obtained. In this report, some electromyographic findings are described and discussed. This series contain 26 cases (male 23, female 3). Age of onset: 13-33 years old (mean 19.4 years old). Clinical duration: 2-32 years old (mean 9.0 years). Only 6 cases (23%) showed trauma as the past history (Table 2). We classified 26 cases in three groups (UL: unilateral, BP: bilateral, one-side predominant, BS: bilateral symmetrical) based on the laterality of physical findings (amyotrophy, weakness, finger tremor, etc.) (Table 3). Conventional needle EMG were done in all cases and these findings were judged by the criteria which we defined as Fig. 2. In some cases, conduction velocity (MCV & SCV) were measured. Needle EMG showed more selective and localized distribution of NGP (neurogenic pattern) in the hand muscles, the forearm muscles except for M. brachioradialis, and M. triceps brachii on the atrophied sides of the arm in all clinical groups (UL, BP, BS) (Table 4.5). On the normal side of bilaterally examined cases of UL group, NGP was shown in 9/11 cases, buts its distribution seemed to be slightly restricted in the more distal part. Thus, in this disorder, 22/26 cases (77%) were electromyographically affected on the bilateral sides, although the clinical feature was mostly unilateral. The clinical features and pathological process seemed to be established in a few years after the onset without the apparent tendency of further progression. Afterwards, no apparent extension of NGP distribution and increment of grading were observed in the Clinical course. No delay was observed on MCV and SCV. The pathological lesions responsible for these electromyographic changes are discussed, either on spinal segmental origin or on brachial plexus origin, but some ambiguous portions are still remained.