Benign monomelic amyotrophy: a study of twenty-one cases.

A consecutive series of 21 patients with single limb atrophy (monomelic amyotrophy) is reported. Sixteen had lower limb atrophy and five had upper limb involvement. The median age of the onset was 20 years. Characteristic features were sporadic occurrence, wasting confined to one limb, insidious onset with slow progression, stabilizing in 1 to 4 years, and absence of pyramidal signs. All the patients with upper limb involvement were male, however in our cases with lower limb amyotrophy there were no male preponderance. We observed wasting of the entire length of the lower limbs in six patients. There were nine cases with amyotrophy restricted to the leg and one with amyotrophy only in the thigh. In the upper limb in four cases the involvement was distal and in one patient the atrophy was proximal. The electromyographic features were suggestive of anterior horn disease not only in the affected limb but also, in some cases, in clinically uninvolved limb. Cervical or lumbar MRI was normal. MRI of the lower limb disclosed increased signal intensity in the gastrocnemius and soleus muscles in one patient suggesting denervation.