• inflammatory muscle disease
• dermatomyositis
• polymyositis
• inclusion body myositis

The inflammatory myopathies are rare. No accurate figures for incidence or prevalence are available but if one takes the two most common conditions, dermatomyositis and inclusion body myositis, their combined annual incidence is probably less than 200 new cases per annum in the UK (population ~60 million). Given that patients with inflammatory myopathy may present to, and be managed within, one of several specialties (for example, dermatology, rheumatology, neurology, general medicine), and that there are about 250 neurologists in the UK, it is apparent that most general neurologists are going to see these conditions on average probably no more than once every couple of years. In perhaps 70% of cases, the diagnosis and management are straightforward and successful early experience may encourage a sense of competence that is only shaken when things do not go as expected. There is no doubt that patients are best served by somebody with specific expertise and interest in these rare conditions, and ideally there should be such a specialist in each region to whom they can be referred.

This article will consider the classification of the inflammatory myopathies, the clinical features of the so-called idiopathic inflammatory myopathies, and approaches to their diagnosis and management. With respect to drug treatment there is an absolute dearth of randomised controlled trials and the best advice that can be offered is based on “expert opinion”. Multicentre trials are desperately needed. Emphasis will be placed on pitfalls in diagnosis and management. Current views on pathogenesis will be noted, but many areas of ignorance remain and it is likely that the next few years will see a major revision of opinions.

Some fundamental issues and take home messages are summarised in box 1.