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Sporadic inclusion body myositis (sIBM) 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. In sporadic inclusion body myositis [MY-oh-sigh-tis] 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 (vacuole)s, deposits of abnormal proteins within the cells and in filamentous inclusions (hence the name inclusion body myositis).
sIBM is a rare disease, 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.[1] 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 you (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.
How sIBM affects individuals is quite variable as is the age of onset (which generally varies from the forties upwards). Because sIBM affects different people in different ways and at different rates, there is no “textbook case.”
Eventually, sIBM results in general, progressive muscle weakness. The muscles in the thighs called the quadriceps and the muscles in the arms that control finger flexion– making a fist — are usually affected early on. Common early symptoms include frequent tripping and falling, weakness going up stairs and trouble manipulating the fingers — turning doorknobs, gripping keys, etc.
During the course of the illness, the patient’s mobility is progressively restricted as it becomes hard for him or her to bend down, reach for things, walk quickly and so on. Many patients say they have balance problems and fall easily, as the muscles cannot compensate for an off-balanced posture. Because sIBM makes the leg muscles weak and unstable, patients are very vulnerable to serious injury from tripping or falling down. Although pain has not been traditionally part of the “textbook” description, many patients report severe muscle pain, especially in the thighs.
When present, dysphagia is a progressive condition in patients with inclusion body myositis and often leads to death from aspiration pneumonia. Dysphagia is present in from 40 to 85% of IBM cases. [2]
Patients with sIBM usually eventually need to resort to a cane or a walker and in most cases, a wheelchair eventually becomes a necessity.
From a recent article: “The progressive course of s-IBM leads slowly to severe disability. Finger functions can become very impaired, such as for manipulating pens, keys, buttons, and zippers, pulling handles, and firmly grasping handshakes. Arising from a chair becomes difficult. Walking becomes more precarious. Sudden falls, sometimes resulting in major injury to the skull or other bones, can occur, even from walking on minimally-irregular ground or from other minor imbalances outside or in the home, due to weakness of quadriceps and gluteus muscles depriving the patient of automatic posture maintenance. A foot-drop can increase the likelihood of tripping. Dysphagia can occur, usually caused by upper esophageal constriction that often can be symptomatically improved, for several months to years, by bougie dilation per a GI or ENT physician. Respiratory muscle weakness can sometimes eventuate.” [3]
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