Monomelic amyotrophy is an untreatable, focal, motor neuron disease that primarily affects young (15 - 25 year-old) males in India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 and Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. MMA is marked by insidious onset of muscular atrophy

Atrophy

Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...

, which stabilizes at a plateau after two to five years from which it neither improves nor worsens. There is no pain or sensory loss associated with MMA. Unlike other lower motor neuron diseases, MMA is not believed to be hereditary and fasciculation

Fasciculation

A fasciculation , or "muscle twitch", is a small, local, involuntary muscle contraction and relaxation visible under the skin arising from the spontaneous discharge of a bundle of skeletal muscle fibers...

s (involuntary muscle twitches) are rare.

EMG

Electromyography

Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...

 tests reveal loss of the nerve supply, or denervation, in the affected limb without conduction block (nerve blockage restricted to a small segment of the nerve). Increased sweating

Sweating

Perspiration is the production of a fluid consisting primarily of water as well as various dissolved solids , that is excreted by the sweat glands in the skin of mammals...

, coldness and cyanosis

Cyanosis

Cyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...

 have been reported for a few patients, indicating involvement of the sympathetic nervous system

Sympathetic nervous system

The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

.

While MMA will cause weakness and/or wasting in only one limb, EMG

Electromyography

Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...

 and NCV

Nerve conduction velocity

Nerve conduction velocity is the speed at which an electrochemical signal propagates down a neural pathway. Many things can affect this, including axon diameter, myelination, the internal resistance of the axon, and temperature. Nerve conduction velocity differs from species to species, and to a...

 tests often show signs of reinnervation

Reinnervation

In living tissues, reinnervation describes the process by which post-synaptic neurons form new synapses or increase existing synaptic efficacy in order to compensate for a lack of pre-synaptic input from dead or otherwise dysfunctional pre-synaptic neurons....

 in the unaffected limbs.

Treatment

There is no cure for MMA. Treatment consists of muscle strengthening exercises and training in hand coordination.

Prognosis

The symptoms of MMA usually progress slowly for one to two years before reaching a plateau, and then remain stable for many years. Disability is generally slight. Rarely, the weakness progresses to the opposite limb. There is also a slowly progressive variant of MMA known as O'Sullivan-McLeod syndrome, which only affects the small muscles of the hand and forearm and has a slowly progressive course.

Epidemiology

MMA occurs in males between the ages of 15 and 25. Onset and progression are slow. MMA is seen most frequently in Asia, particularly in Japan and India; it is much less common in North America.

External links

• MND Association
• Overview at Washington University