Long-term follow-up of 44 patients with brachial monomelic amyotrophy

Monomelic amyotrophy of a single upper limb termed "brachial monomelic amyotrophy" (BMMA) is a benign lower motor neuron disorder in the young, with male preponderance, insidious onset of atrophy and weakness, electromyographic evidence of neurogenic pattern without conduction block, slow progression for 2-4 years followed by a stationary course. The aim of the study was to determine whether (i) atrophy and weakness in the affected limb progresses beyond 5 years; (ii) the illness spreads to the other limbs; and (iii) the disease progresses to amyotrophic lateral sclerosis.

Forty-four patients who had a duration of illness of 5 years or more at the last follow-up examination were included in the study. Assessment of symptom profile, neurologic deficit and disability was performed at variable intervals during the follow-up period.

Progression of the disease was seen in 37 (84.1%) patients, up to 5 years in 35 (79.5%), 6 years in one and 8 years in another patient. In seven patients (15.9%) the atrophy was accidentally noticed and no further change in the neurologic deficit was observed thereafter. Subsequent to attaining a stationary course, none of the 44 subjects developed fresh symptoms or signs during a mean follow-up period of 9.7 years (range 2.5-23). The mean duration of illness at last follow-up was 12.8 years (range 5-26.5) and in 22 (50%) subjects the disease duration was more than 10 years. Seven patients (15.9%) at presentation had minimal involvement of contralateral upper limb with gross asymmetry and later one more patient developed similar features. Thus, in only a small proportion (18.2%) of patients the neurologic deficit had extended beyond the confines of one upper limb. None of the patients developed involvement of cranial nerves, lower limbs or pyramidal signs.

Progression of the neurologic deficit in the affected limb was seen up to 5 years in the majority followed by a stationary phase with no evidence of fresh neurologic deficit during the follow-up period. Spread to the contralateral upper limb with minimal neurologic deficit was seen in less than a fifth of the patients, but involvement of lower limbs was not observed. BMMA did not evolve to amyotrophic lateral sclerosis. These observations underscore the benign and self limiting course of BMMA.