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WINTER 2024 InTouch | 15 INCLUSION BODY MYOSITIS Continued over ... The first muscles affected in inclusion body myositis are usually those of the wrists and fingers, and the muscles at the front of the thigh. The muscles that lift the front of the foot also may be affected. more than the other) is common in IBM, distinguishing it from other muscle diseases. Dysphagia (difficulty swallowing) is present in about 40% of patients who are diagnosed with IBM, and becomes more common as the disease progresses, ultimately affecting close to 80% of those with IBM. Mild weakness of the facial muscles can also occur. The rate of progression of weakness is variable, but observational studies have shown that about half will require a wheelchair within 10 years of diagnosis. IBM does not directly affect cardiac or respiratory muscles. Recent epidemiological data show that IBM is associated with a slightly reduced life span (on average, 3 years less than controls), likely related to dysphagia resulting in aspiration pneumonia. A small increase in risk of haematologic malignancies was also found, as well as a moderate increase in risk of autoimmune disorders, particularly Sjogren syndrome. Causes of IBM The understanding of the primary cause of IBM is evolving, making it an important and active area of research due to its implications on finding effective treatments. It is not clear whether the primary driver of the disease is degenerative (i.e., abnormal aging) or inflammatory. Traditionally, the degenerative theory was predominant, supported by the observation that immune suppressant drugs have no apparent effect on the course of the disease, unlike in other inflammatory myopathies. However, recent evidence suggests that immune-mediated inflammation may be the primary driving factor of the disease which then sets off a cascade of mitochondrial dysfunction and muscle cell degeneration. While IBM is not inherited disease, per se, there is evidence that genetic factors play a role, particularly as it pertains to the genetic makeup of one’s immune system. While the specific underlying cause of Inclusion Body Myositis (IBM) is still being investigated, the effects of the disease processes are more evident. We know that inflammation is occurring due to the presence of inflammatory cells invading otherwise apparently healthy muscle cells, as seen under a microscope. Additionally, we observe a buildup of toxic protein aggregates (clumps) similar to those found in the brains of people with Alzheimer’s disease. This suggests an error in the control of protein folding and degradation, indicative of degeneration. As the muscle fibres degenerate and die, they are replaced by fat, a process known as fatty infiltration. This phenomenon is particularly well visualized with imaging studies such as MRI and ultrasound. Diagnosis of IBM Inclusion body myositis is suspected when a physical exam corroborates the typical signs of asymmetric weakness in the finger flexors and thigh muscles. It is also important to confirm the following to rule out other conditions that are similar: • Presence of diminished tendon reflexes at the knees and ankles. • Relatively preserved sensation. • No cognitive impairment. • No abnormality of coordination. • No rash (which may indicate the alternative diagnosis of dermatomyositis). When IBM is suspected due to the presentation as described above then further tests may be requested to support the diagnosis: • A blood test for creatine kinase may show normal or mildly elevated levels. • Nerve conduction studies are usually normal, though some patients may have a mild associated peripheral neuropathy. • Electromyography typically demonstrates changes consistent with myopathy (disorder of the muscles). It may be necessary to test several muscles. • Muscle imaging (MRI or ultrasound) findings can support the diagnosis