Definition of Motor neuron disease

Motor neuron disease: A group of neurological diseases characterized by steadily progressive deterioration of the motor neurons in the brain, brainstem and spinal cord that send instructions in the form of electrical impulses to the muscles, leading to muscle weakness and wasting.

Motor neuron disease (MND) usually first affects the arms or legs. Then shoulders and other muscles may be affected. Weakness and wasting in the muscles of the face and throat may cause problems with speech, chewing and swallowing. MND does not affect touch, taste, sight, smell or hearing, nor does it directly affect bladder, bowel, or sexual function. In the vast majority of cases, the intellect remains unchanged.

Most people develop MND over the age of 40. The highest incidence is in the range of 50 to 70 years of age. Men tend to have MND slightly more often than women.

The clinical subtypes of MND are distinguished by the major site of degeneration of the motor neurons and include amyotrophic lateral sclerosis (Lou Gehrig's disease), progressive spinal muscular atrophy, progressive bulbar palsy, and primary lateral sclerosis.

(In amyotrophic lateral sclerosis there is involvement of upper, lower, and brainstem motor neurons. In progressive spinal muscular atrophy and related syndromes, the motor neurons in the spinal cord are primarily affected. With progressive bulbar palsy, the initial degeneration occurs in the brainstem. In primary lateral sclerosis, the cortical neurons are affected in isolation.)

Synonyms for MND include anterior horn cell disease, familial motor neuron disease, lateral sclerosis, lower motor neuron disease, motor neurone disease, and upper motor neuron disease.