Monomelic amyotrophy

Disease Overview

Monomelic amyotrophy (MMA) is a rare disease that causes muscle weakness in the upper extremities. MMA affects the lower motor neurons. Lower motor neurons are cells that help communicate information from the brain to the muscles that are involved in movement (skeletal muscles). Specifically, monomelic amyotrophy causes weakness and loss of muscle mass in the arms and fingers. Symptoms of the disease typically begin between the ages of 14-25 years-old. The disease is most common in Asia, especially in Japan and India. Males are more likely to develop the disease than females.[14326]

The exact cause of monomelic amyotrophy is unknown. It is possible that the disease is caused by movement of the sac that surrounds the spinal cord due to repeated downward movement (flexion) of the neck. Monomelic amyotrophy can sometimes run in families, but it is not thought to be caused by a specific genetic change. Diagnosis of the disease is based on imaging studies and electromyography (EMG) consistent with the disease. Treatment options may include muscle strengthening exercises and neck bracing.[14326]

Synonyms

• Hirayama disease
• Spinal muscular atrophy juvenile nonprogressive
• Benign focal amyotrophy
• Juvenile muscular atrophy of distal upper extremity (JMADUE)
• Juvenile muscular atrophy of distal upper limb