Definition, Etiology, and Incidence

Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig disease after the famous New York Yankees baseball player, is a devastating neurologic disorder that selectively affects motor function with an unknown origin, characterized by progressive muscle atrophy with hyperreflexia that results from denervation, and results in muscle weakness, disability, respiratory insufficiency, and eventually death.

ALS is a rare, debilitating, and incurable neurologic disease, has an annual incidence of 0.5-2 per 100,000 population, is primarily a disorder of middle to late adulthood, affecting people most frequently in their fifties, with men developing the disease nearly twice as often as women. The median survival duration for patient is approximately 3 years, yet approximately 20% of patients survive greater than 5 years, and 10% will survive for greater than 10 years.

As the main area of involvement is the motor neurons of the brain and spinal cord, ALS affects motor neurons in three locations as follows: the anterior horn cells (lower motor neurons – LMNs) of the spinal cord; the motor nuclei of the brain stem, particularly the hypoglossal nuclei; and the upper motor neurons (UMNs) of the cerebral cortex. The death of the LMNs leads to denervation, with subsequent shrinkage of musculature and muscle fiber atrophy. It is this fiber atrophy, called amyotrophy, which appears in the name of the disease. The loss of nerve fibers in lateral columns of the white matter of the spinal cord, along with fibrillary gliosis, imparts a firmness or sclerosis to this CNS tissue. The term lateral sclerosis designates these changes.

A remarkable feature of the disease is that the entire sensory system, the regulatory mechanisms of control and coordination of movement, and the intellect remain intact.

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