The inflammatory myopathies are divided into three major and distinct subsets as polymyositis(PM), dermatomyositis(DM), and inclusion body myositis(IBM). This distinction is based on unique clinical, demographic, laboratory, histologic,therapeutic, prognostic, and immunopathologic criteria.Although the causes of PM, DM, and IBM are unknown, autoimmune mechanisms are implicated, as supported bytheir association with other putative or definite autoimmune diseases or viruses, the evidence for a T cell-mediatedmyocytotoxicity or complement-mediated microangiopathy, the presence of various autoantibodies and their responseto immunotherapies. But in IBM the immune-mediated process is weaker and IBM patients do not readily respond toimmunotherapies, there are convincing immunopathological signs to suggest that a definite autoimmune component,similar to that seen in PM, also plays a role in the cause of IBM.
Among drug-induced myopathy, steroids are probably the most common cause. The risk of steroid myopathy(SM)increases with the dose and duration of use. It is typically a proximal myopathy, preferentially affecting the hip girdlemuscles. Motor and sensory nerve conduction studies are normal. The needle EMG is usually within the normal rangeor may be minimally abnormal. Occasionally, low-amplitude, short-duration MUAPs may be seen in the proximal muscles.Of note, abnormal spontaneous activity is not seen. This point is often very useful in differentiatingpolymyositis(PM) from SM. It is common for patients with PM to be treated with steroids, respond well, and then havethe steroids tapered. If muscle weakness then returns, it may be very difficult to differentiate recurrent PM from SM onclinical grounds. The presence of abundant abnormal spontaneous activity strongly suggests PM rather than SM.
Chronic graft-versus-host disease (GVHD) is a well-known complication of allogeneic bone marrow transplantation (BMT)and has heterogeneous manifestations, with multi-organ involvement. Recently, polymyositis (PM) was reported to be a raremanifestation of chronic GVHD. Here, we report a 30-year-old woman who was diagnosed with PM after allogeneic BMT.
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