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Muscle atrophy is the wasting or loss of muscle tissue.

There are two types of muscle atrophy.

Disuse atrophy occurs from a lack of physical exercise. In most people, muscle atrophy is caused by not using the muscles enough. People with sedentary jobs, medical conditions that limit their movement, or decreased activity levels can lose muscle tone and develop atrophy. This type of atrophy can be reversed with vigorous exercise or better nutrition.

Bedridden people can have significant muscle wasting. Astronauts who are away from the Earth's gravity can develop decreased muscle tone and lose calcium from their bones after just a few days of weightlessness.

The most severe type of muscle atrophy is neurogenic atrophy. It occurs when there is an injury to, or disease of a nerve. This type of muscle atrophy tends to occur more suddenly than disuse atrophy.

Examples of diseases affecting the nerves that control muscles:

• Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease)
• Guillain-Barre syndrome
• Polio (poliomyelitis)

Even minor muscle atrophy usually causes some loss of movement or strength.

Some muscle atrophy occurs normally with aging. Other causes may include:

• Amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease)
• Burns
• Guillain-Barre syndrome
• Injury
• Long-term corticosteroid therapy
• Long-term immobilization
• Motor neuropathy (such as diabetic neuropathy)
• Muscular dystrophy
• Osteoarthritis
• Polio
• Rheumatoid arthritis
• Spinal cord injury
• Starvation
• Stroke

An exercise program (under the direction of a therapist or doctor) is recommended. This may include exercises in water to reduce the muscle workload, and other types of rehabilitation.

People who cannot actively move one or more joints can do exercises using braces or splints.

Call your doctor for an appointment if you have unexplained or long-term muscle loss. You can often see this when you compare one hand, arm, or leg to the other.

The doctor will perform a physical examination and ask questions about your medical history and symptoms, including:

• When did the muscle atrophy begin?
• Is it getting worse?
• What other symptoms do you have?

The doctor will look at your arms and legs and measure muscle size to try to determine which nerve or nerves are affected.

Tests that may be performed include:

• CT scans
• Electromyography
• MRI scans
• Muscle biopsy
• Nerve conduction studies
• X-rays

Treatment may include ultrasound therapy and, in some cases, surgery to correct a contracture.

Muscle wasting; Wasting; Atrophy of the muscles

Arend WP, Lawry GV. Approach to the patient with rheumatic disease. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 277.

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.