Infections directly affecting muscle are rare in the Western world. Similarly eosinophilia-myalgia syndrome, toxic oil syndrome and macrophagic myofasciitis are very rare, and the latter essentially confined to France. There is increasing evidence that statins may induce an immune-mediated necrotising myopathy which persists on statin withdrawal and responds to immunosuppressant drug therapy  and . It is of note that statins can also induce potentially fatal rhabdomyolysis through presumed metabolic dysfunction–the condition is self-limiting but in the immediate aftermath the appearance of a necrotising myopathy may be very similar to the immune-mediated
disorder. Granulomata in muscle are sometimes sought in order to confirm a diagnosis of sarcoidosis, but clinically significant muscle disease is rare. A clinical pattern similar to sIBM, with distal Bcl2 inhibitor weakness affecting the finger flexors, has been described . Response to immunosuppressant S3I-201 chemical structure therapy is often poor. As with sarcoidosis, many
vasculitides may produce changes in muscle that can aid diagnosis, but clinically significant muscle involvement is rare. The frequent coexistence of myositis with symptoms and signs of CTD is striking. Previous authors have distinguished, in arguably somewhat arbitrary fashion, between associated and overlapping conditions . For the purposes of this classification I have considered two scenarios. Firstly, the occurrence of myositis with a clearly defined all CTD–the CTD should fulfill its own diagnostic criteria. Rarely PM may be seen in association with rheumatoid arthritis. Muscle involvement may also be secondary to neuropathy and vasculitis. Equally rarely, SLE and Sjögren’s syndrome can be associated with either DM or PM. Myositis is somewhat more common in association
with scleroderma and mixed connective-tissue disease (MCTD), and is often of the “non-specific” type. The anti-PM/Scl antibody may be seen in patients with scleroderma-myositis, but also in patients with isolated myositis. MCTD is a somewhat contentious entity–clinical features in addition to myositis include swollen hands (with acrosclerosis), Raynaud’s phenomenon, pulmonary involvement, and the presence of the extractable nuclear antigen U1 snRNP. The anti-synthetase syndrome was described earlier. The immune-mediated disorders include DM and PM defined by the clinical and immunopathological features discussed earlier. In particular, PM requires the specific finding of endomysial inflammatory infiltrates surrounding, and preferably invading, non-necrotic muscle fibres which are expressing MHC-1. In both categories, patients may have features of a CTD but not with enough features to allow the diagnosis of a specific condition. Clinical features may include Raynaud’s phenomenon, arthralgia, and arthritis, and serological markers anti-nuclear antibodies, rheumatoid factor, anti-PM/Scl, and others.