Sarcoid myopathy also often responds disappointingly to treatment. Specific features on muscle biopsy have become paramount in subclassifying the inflammatory myopathies. As noted, the fundamental finding is the presence of inflammatory infiltrates. However, the presence of such infiltrates is not in itself proof of an inflammatory myopathy–by which we mean that an inflammatory process is the primary cause of the myopathy. A major confusing factor clinically see more is that similar infiltrates may be seen in many dystrophies (i.e. genetically determined disorders) and this not infrequently leads to erroneous diagnosis

and treatment ([1] in this edition). This has been noted particularly for dysferlinopathy, but is also seen in other dystrophies. It is possible that this presumed secondary inflammatory process may contribute to the clinical picture and trials of steroids in dysferlinopathy are currently in progress. Experience to date suggests that the find more use of steroids to treat secondary inflammation in the dystrophies is largely ineffective–and it is very tempting to think that this may be analogous to what we see in sIBM. Thus there is the school of thought that sIBM is primarily a degenerative disorder and that the inflammatory

changes noted are only a secondary epiphenomenon, which would explain the lack of response to immunosuppression [2] and [3]. Study of the specific immunopathological changes

in DM and PM has led to the current concept that both are autoimmune diseases but with very until different effector mechanisms. Thus, DM is a complement-dependent disorder in which immune attack destroys capillaries leading to a form of ischaemic myopathy. PM on the other hand is due to a MHC1-restricted, cytotoxic T-cell-mediated destruction of muscle fibres [4]. As will be discussed elsewhere, some argue that the immunopathological subclassification of the inflammatory myopathies is more important than classification based on clinical and other pathological criteria. The presence of myositis-specific antibodies undoubtedly defines certain subcategories of inflammatory myopathy. To date their value has been restricted in part because of lack of general availability, although that is changing and commercial diagnostic kits are now available. They lack sensitivity, being present in somewhere between a third and one half of all cases. There is no evidence that they are in themselves pathogenic and in many instances may be unimportant epiphenomena, but nevertheless may prove to be useful diagnostically. Many classifications have included electromyographic findings.