According to The National Institute of Neurological Disorders and Stroke, motor neuron diseases are a group of progressive neurological disorders that destroy cells that control muscle activity, including speaking, walking, breathing, and swallowing. Motor neuron diseases may be inherited or acquired, and occur in all age groups. Motor neurons are divided into upper--those in the brain, and lower-- those in the brain stem and spinal cord. There are sporadic and inherited causes of motor neuron disease.
Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis is a usually fatal disease that causes an inexorable progressive loss of upper and motor neurons; it is the most devastating of the neurodegenerative diseases. Amyotrophic lateral sclerosis is a sporadic disease; however, 5 to 10 percent of cases are inherited.
Any muscle group may be involved first. According to "Essentials of Clinical Neuroanatomy and Neurophysiology," classically, this disease starts with weakness of the muscles of the hands and arms, followed by paralysis of the legs. According to "Harrison's Principles of Internal Medicine," if motor neurons in the brainstem are involved, the patient experiences difficulty chewing, swallowing and movement of the face and tongue. The muscles of respiration may be involved early leading to death.
Spinal Muscular Atrophies
Spinal muscular atrophies are inherited diseases that selectively affect lower motor neurons; there are three types that affect infants, children and juveniles, respectively. Approximately 1 in 6000 babies born are affected, and about 1 in 40 people are genetic carriers. Affected infants die rapidly.
According to Families of Spinal Muscular Atrophy, the involved motor neurons affect muscles used for activities such as crawling, walking, head and neck control, and swallowing. The muscles in the shoulders, hips, and back are often most severely affected. Sometimes it is necessary to surgically insert a steel rod in the patient's spine so that he/she may sit upright. Weakness in the legs is usually more pronounced than in the arms. Involvement of breathing and coughing muscles increases the risk for pneumonia.
Post-Polio Syndrome
Post-polio syndrome affects polio survivors who, many years later, develop new weakness in muscles previously damaged by the poliomyelitis virus and in muscles that were unaffected. According to Dr. Richard Bruno, Chair, Post-Polio Institute at Englewood (N.J.) Hospital, post-polio syndrome causes unexpected and often disabling symptoms, including profound fatigue, muscle weakness, muscle and joint pain, sleep disorders, cold intolerance, and difficulty swallowing and breathing. The cause of post-polio syndrome is unknown; however, the new weakness seems related to degeneration of nerve terminals remaining after the initial illness.
References
- National Institute of Neurological Disorders and Stroke: Motor Neuron Diseases Fact Sheet
- "Harrison's Principles of Internal Medicine"; Dennis Kasper, M.D.; 2005
- "Essentials of Clinical Neuroanatomy and Neurophysiology"; Ronald Clark; 1979
- Englewood Hospital's Post-Polio Institute
- Families of Spinal Muscular Atrophy
