What is inclusion body myositis?

Inclusion body myositis (IBM) is an inflammatory and degenerative muscle disease that causes painless weakening of muscle.

IBM gets worse slowly and is sometimes misdiagnosed as treatment-resistant polymyositis, another inflammatory muscle disease that causes muscle weakness. IBM also may be misdiagnosed as amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease).

Symptoms of the disease usually begin after the age of 50, although the disease can occur earlier. IBM occurs more frequently in men than in women and is the most common muscle disease in people aged 50 and older.

What causes IBM?

The cause of IBM is unknown. Because of the inflammation associated with IBM, some doctors think the disease is a form of autoimmune disorder. In this kind of disorder, the body’s immune system goes awry and attacks its own tissues – in this case, the muscles. Some experts have linked IBM to infection by a virus that has yet to be identified. Other researchers believe that the primary problem in IBM is an age-related inability of the muscle to deal with destructive chemicals.

What are the symptoms of IBM?

In IBM, the onset of muscle weakness usually is gradual, occurring over months or years. Falling and tripping usually are the first noticeable symptoms. For some people, IBM begins with weakness in the hands. People with IBM may have:

  • Difficulty with gripping, pinching, and buttoning
  • Weakness of the wrist and finger muscles
  • Atrophy (shrinking or wasting) of the muscles of the forearms
  • Weakness and visible wasting of the quadriceps muscles (the large muscles on the front part of the thighs)
  • Weakness of the lower leg muscles, below the knees
  • Weakness of the esophageal muscles, which can cause dysphagia (difficulty swallowing) in about 30 to 40 percent of patients
  • Weakness of other muscle groups as the disease progresses

How is IBM diagnosed?

Doctors use a muscle biopsy to diagnose IBM. After giving an anesthetic, a doctor takes a sample of tissue from one of the affected muscles to be looked at in a laboratory.

When viewed under the microscope, the muscle cells of persons with IBM contain vacuoles (rounded empty spaces). Within the vacuoles, there are usually abnormal clumps of several proteins including one called amyloid. The protein clumps, or inclusion bodies, give IBM its name. This is the hallmark of IBM.

How is IBM treated?

There is no effective course of treatment for IBM. The disease is not responsive to corticosteroids and immunosuppressive drugs – two drugs that often treat inflammatory or autoimmune conditions. Some evidence suggests that intravenous immunoglobulin may help slightly in a small number of cases, but the benefit does not last long. Physical therapy may be helpful in maintaining mobility and helping to keep joints mobile. Other therapy, including treatments for the swallowing problems, is symptomatic and supportive.

For more information, please see the following:

Muscular Dystrophy Association - USA
National Office
222 S. Riverside Plaza, Suite 1500
Chicago, IL 60606
Toll free: 800-572-1717

Myositis Association
1737 King Street
Suite 600
Alexandria, VA 22314
Tel: 703-299-4850 (DC Area)
Toll free: 800-821-7356
Fax: 703-535-6752
Email: tma@myositis.org

American Autoimmune Related Diseases Association, Inc.
22100 Gratiot Avenue
Eastpointe, MI 48021
Tel: 586-776-3900
Fax: 586-776-3903


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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 9/22/2015…#15700