Monomelic amyotrophy (MMA) is a rare disease of the nerves that control voluntary movements of the limbs.

Monomelic amyotrophy may also be known as benign focal amyotrophy, single limb atrophy, Hirayama syndrome or Sobue disease

Monomelic amyotrophy occurs worldwide and is most prevalent in Asia, and especially in Japan and India. According to a report in 1984, MMA of the lower limb occurs in about four in a million people in India.

Treatment primarily consists of rehabilitation measures such as physical therapy and occupational therapy. Severe muscle weakness (present in a minority of cases) may require orthopedic intervention

The main features of MMA are muscle weakness and atrophy in one limb. The weakness and wasting progresses slowly and may spread to the corresponding limb on the opposite side of the body