The main
inflammatory myopathies within the
myositis group include
polymyositis, dermatomyositis and
inclusion-body myositis (IBM). Although potentially treatable, various practical issues have an impact on the response of these conditions to
therapy. The most common reason for therapeutic failure is that the treatment targets the wrong disease, often owing to poor distinction of
polymyositis from difficult-to-treat mimics such as sporadic IBM, necrotizing
myopathies and inflammatory dystrophies. Evidence from uncontrolled studies suggests that
polymyositis and
dermatomyositis respond to treatment with
prednisone at least to some degree. Empirically, adding an immunosuppressive
drug might offer a '
steroid-sparing' effect or perhaps additional benefit.
Intravenous immunoglobulin is proven effective as a second-line agent in patients with
dermatomyositis and also seems to be effective for those with
polymyositis, but offers only minimal and transient benefit to a small proportion of patients with IBM. Small, uncontrolled series suggest other agents such as
rituximab or
tacrolimus might offer some benefit in disease refractory to the aforementioned
therapies, although IBM is resistant to most
therapies. Novel agents are emerging as potential treatment options for all forms of
myositis. This Review highlights common pitfalls in
therapy, discusses emerging new
therapies, and provides a practical therapeutic algorithm.