Inclusion Body Myositis

Inclusion body myositis (IBM) is one of a group of muscle diseases known as inflammatory myopathies, which are characterized by chronic muscle inflammation accompanied by muscle weakness. Other diseases in this family include dermatomyositis (DM), and polymyositis (PM). The onset of muscle weakness in IBM is generally gradual (over months or years) and affects both proximal (close to the trunk of the body) and distal (further away from the trunk) muscles. Muscle weakness may affect only one side of the body. Inclusion body myositis primarily affects men after the age of 50 but can also affect women. The disease generally progresses slowly and does not affect life expectancy of those affected.

Sporadic
Sporadic inclusion body myositis (sIBM) affects people randomly (there appears to be a genetic pattern of inheritance). Evidence of inflammation is present in the muscles when viewed under the microscope.

Hereditary
Hereditary inclusion body myositis (hIBM) lacks some of the inflammatory characteristics of sporadic IBM. This type is caused by a genetic defect and can be passed between generations.

Familial
IBM with inflammation can be present in more than one member of a family and is known as familial IBM (fIBM). It is unclear whether this form is inherited or whether some people have genes that make them susceptible to whatever causes the sporadic form.

Signs and Symptoms
Falling and tripping are usually the first noticeable symptoms of IBM. Other symptoms include:
 * Muscle weakness that affects the flexor muscles of the wrists and fingers (ones that cause the wrist and fingers to bend forward) and other muscles of the fingers
 * Weakness of the quadriceps muscles (the large muscle group on the front of the thigh) and the muscles of the lower legs
 * Weakness of the muscles of the esophagus, which can cause dysphagia (difficulty swallowing)

These symptoms may occur one at a time or appear simultaneously. Together, they can lead to difficulty grasping objects, rising from a sitting position, walking long distances or going up stairs. Weakness of the quadriceps muscles can cause sudden falling, and lower leg weakness can cause difficulty holding the foot up ("foot-drop"), which can lead to tripping. If the esophageal muscles weaken, choking may become a problem when ingesting some types of food or liquids.

Causes
The cause of the sporatic form of IBM is unknown. Theories include an infectious or autoimmune trigger and an accumulation of abnormal protein in the muscle fibers causing a secondary autoimmune response. More than likely, the pathology involves a combination of factors including aging, genetic suceptibility, and environmental factors. The genes that may be involved in sIBM have not yet been identified. Studies are ongoing to determine the genetics of this disease.

The hereditary form of IBM is believed to be caused by mutations in the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) gene, causing an impairment in function of the GNE protein.

Sporadic and familial inflammatory IBM appear share the same clinical, biological, MRI, and histological features. The familial form of the disease occurs in several members of the same family. The genetics of fIBM are still unclear.

Diagnosis
Inclusion body myositis is usually diagnosed by a muscle biopsy. When viewed under the microscope, the muscle cells show vacuoles (empty, round spaces). Within the vacuoles there are clumps of abnormal proteins, one of which is amyloid. These characteristic protein clumps, which are called "inclusion bodies," give this disorder its name. Inflammatory cells (white blood cells) frequently seen in the nearby muscle tissue

Treatment
There is no cure for IBM, nor is there a standard course of treatment.

Medications
The disease is generally unresponsive to corticosteroids and immunosuppressive drugs. Some evidence suggests that intravenous immunoglobulin may have a slight, but short-lasting, beneficial effect in a small number of cases. Prednisone is also used for treatment, although its benefit has not been proven.

Therapies
Physical therapy may be helpful in maintaining mobility. Other therapy is symptomatic and supportive. Occasionally, dysphagia symptoms can be severe enough that a nonsurgical expansion of the throat muscles (called "dilation") or a surgical division of specific throat muscles (called a "cricopharnygeal myotomy") may be needed.

Clinical Trials
A list of U.S. government-sponsored clinical trials is available at ClinicalTrials.gov: inclusion body myositis trials.

Recent discoveries

 * Human T-lymphotropic virus-type I (HTLV-I) infection may be a cause of sporadic inclusion body myositis, according to a recent study.
 * An inclusion body myositis functional rating scale was developed and appears to be a valid and reliable measure of the severity of the disease.
 * The clinical and pathological methods of diagnosing inclusion body myositis are discussed. Skeletal muscle biopsy was determined to be the most accurate method of diagnosing the disease.

Current research

 * The use of alemtuzumab to improve muscle strength in patients with sIBM is being studied for efficacy.
 * The major genetic risk and protective factors for idiopathic inflammatory myopathies (IIM) are being studied.

Expected Outcome
IBM is generally resistant to all therapies and its rate of progression appears to be unaffected by currently available treatments. The disease (and its associated muscle weakness) usually progresses slowly and has a steady course (does not fluctuate). A cane, walker or wheelchair may be required to maintain mobility, but the disease doesn't seem to affect life expectancy.