Amyotrophic lateral sclerosis disease, also called Lou Gehrig's disease, is a progressive neurodegenerative disease that attacks nerve cells responsible for voluntary movement. The degeneration of motor neurons causes them to die, resulting in the brain's inability to control muscle movement. ALS is 100 percent fatal, reports the ALS Association.
Motor neurons located in the brain, brain stem, and spinal cord facilitate communication between the nervous system and the voluntary muscles of the body. ALS causes both motor neurons in the brain and motor neurons in the spinal cord to die, ceasing communication with the body's muscles. When the muscles no longer receive these signals, they become weak, atrophy and develop fine twitches. ALS affects all voluntary muscles, causing individuals to lose strength and their ability to move their arms, legs and body. When ALS attacks the muscles that regulate breathing, most individuals succumb to respiratory failure, according to the National Institute of Neurological Disorders and Stroke.
The early symptoms of ALS include weakness in the legs, ankles and feet; muscle cramps and twitching in the arms and shoulders; slurred speech and difficulty swallowing; and difficulty walking or tripping. ALS does not usually impact bladder control or cognitive abilities, reports Mayo Clinic.