Inclusion body myositis (IBM) is an inflammatory muscle disease, characterized by slowly progressive weakness and wasting of both distal and proximal muscles, most apparent in the muscles of the arms and legs. There are two types: sporadic inclusion body myositis (sIBM) and hereditary inclusion body myopathy (hIBM).
In sporadic inclusion body myositis muscle, two processes, one autoimmune and the other degenerative, appear to occur in the muscle cells in parallel. The inflammation aspect is characterized by the cloning of T cells that appear to be driven by specific antigens to invade muscle fibers. The degeneration aspect is characterized by the appearance of holes in the muscle cell vacuoles, deposits of abnormal proteins within the cells and in filamentous inclusions (hence the name inclusion body myositis).
sIBM is a rare yet increasingly prevalent disease, being the most common cause of inflammatory myopathy in the over 50s; the most recent research, done in Australia, indicates that the incidence of IBM varies and is different in different populations and different ethnic groups. The authors found that the current prevalence was 14.9 per million in the overall population, with a prevalence of 51.3 per million population in people over 50 years of age. As seen in these numbers, sIBM is an age-related disease – its incidence increases with age and symptoms usually begin after 50 years of age. It is the most common acquired muscle disorder seen in people over 50, although about 20% of cases display symptoms before the age of 50. Weakness comes on slowly (over months or years) and progresses steadily and usually leads to severe weakness and wasting of arm and leg muscles. It is slightly more common in men than women. Patients may become unable to perform daily living activities and most require assistive devices within 5 to 10 years of symptom onset. sIBM is not considered a fatal disorder – barring complications, all things being equal, sIBM will not kill (but the risk of serious injury due to falls is increased). One common and potentially fatal complication is dysphagia. There is no effective treatment for the disease.
Read more about Inclusion Body Myositis: Classification, Signs and Symptoms, Causes, Genetic Aspects of SIBM, Differential Diagnosis, Diagnosis, Treatment, Other Related Disorders
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