| Disease Name | sporadic and inherited forms | | NMD Category | Myopathy - Disease of Muscle | | Clinical Onset | after age 50 (onset between age 20 to 30 in familial cases) | | Clinical Findings | Inclusion body myositis (IBM) is an inflammatory disorder seen chiefly in mature males that currently is thought to be autoimmune-mediated and acquired, althougth one in ten cases may be hereditary. Average age at onset is 53 years, but the disorder can occur in any age group and women are affected. Falling and tripping are usually the first noticeable symptoms of IBM. For some individuals the disorder begins with weakness in the hands, causing difficulty with common tasks such as buttoning a shirt. The symptoms differ slightly from other inflammatory myopathies in that the weakness typically affects the distal and flexor muscles of the hands and quadriceps muscles of the legs more severely than other muscle groups. Progressive weakness and atrophy involves the arms, legs and hands, especially the thighs, wrists and fingers. Dysphagia will ocassionally be an initial symptom. Facial weakness and swallowing difficulties have been reported in about 50% of cases. Atrophy of the forearms is also characteristic.
Individuals with IBM may experience weakness, pain, tenderness, and/or degeneration (atrophy) of affected muscles as well as diminished involuntary muscle contractions (deep tendon reflexes). In addition, in some cases, affected individuals may also have impaired nerve transmission to certain muscles (peripheral neuropathy), contributing to muscle thinning and weakness. Biopsy of muscle tissue may reveal abnormal levels of inflammatory cells as well as abnormal membrane-bound cavities (vacuolated inclusion bodies) within muscle tissue. In most cases, the cause of IBM is unknown.
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| | Diagnostic Work-up | The diagnosis of inclusion body myositis is suspected in the presence of the history and examination compatible with a chronic acquired muscle disease.
Once IBM is suspected, initial diagnostic steps include measuring serum CK and a muscle biopsy. Muscle biopsy shows mild to moderate inflammation, atrophic denervated fibers, and characteristic "rimmed vacuoles," as well as some muscle fibers with eosinophilic inclusions. Abnormal deposits of a substance called amyloid may be seen upon histologic examination in and around the vacuoles and inclusions.
Differential Diagnosis: Absence of fever, headache, and joint and muscle pain suggests polymyositis or dermatomyositis. Also rule out distal myopathy. Absence of inflammation points to an alternative diagnosis such as one of the inclusion body myopathy.
| | Treatment Notes | Treatment is symptomatic and supportive. IBM has not been responsive to treatment with cortcosteroids and other immunosuppressie drugs. Some evidence suggests that immunoglobulin may have a slight, but transient, beneficial effect in some cases. Physical therapy is helpful in maintaining mobility.
Progression: Slowly progressive (more so in men than in women).
See Diagnostic Criteria for Neuromuscular Diseases http://www.enmc.org/nmd/diagnostic.html.
| | Protein ID | 21 | | Gene Location | | | Abstract | Inclusion body myositis (IBM) is an inflammatory muscle disease characterized by slow and steadily progressive muscle weakness and atrophy of the muscles. Newly diagnosed individuals may become confused when they seek information about inclusion body myositis and come across information about hereditary inclusion body myopathy. While these are all rare disorders that look similar histologically under a light microscope, they are clinically distinct and show distinct phenotypes.
The disorder is very similar to another inflammatory myopathy, polymyositis. A muscle biopsy may be necessary to differentiate between the two myopathies. The sporadic form of IBM is characterized by onset late in life (50-70 years old) and early involvement of the quadriceps muscle. There are also reports of familial forms (onset between 20 and 30 years old) of IBM, apparently inherited as an Autosomal Dominant genetic trait, and often confused with hereditary inclusion body myopathy (in the literature). Both diseases have similar characteristics clinically, but familial forms of IBM run in families. In those cases, muscle biopsy still reveals a predominance of inflammation as in the sporadic form of IBM.
The inclusion body myopathies (not “myositis,” since there is no significant inflammation in the muscle) are a heterogeneous group of muscle disorders characterized by early adult onset (20-40 years old). There are two types of hereditary inclusion body myopathies (HIBM, IBM2), an autosomal dominant form where the quadriceps are one of the first muscles to become weak, and an autosomal recessive form, common among people of Middle Eastern and Jewish heritage, where the quadriceps are among the last muscles to become weak. HIBM has been linked to chromosome 9 and the search for the causative gene(s) is ongoing.
Inclusion body myositis is often diagnosed in cases of polymyositis that are unresponsive to therapy. However, IBM has its own distinctive features. The onset of muscle weakness in IBM is generally gradual (over months or years). Also, IBM, which occurs more frequently in men than women, affects both the proximal (closest to the center of the body) and distal (farthest from the center of the body) muscles.
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