Idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies are a heterogeneous group of uncommon diseases. The incidence rate of IIM is approximately 5 cases per million population, but there appears to be an increase in the rate over the last two decades, particularly in black females. This may be a true increase or due to renewed interest and awareness of the disease and improvement in our ability to diagnose mild disease. There has also been progress in decreasing the mortality rate in IIM perhaps secondary to better treatment and/or the diagnosis of mild disease. The discovery of anti-Jo-1 antibodies has renewed the investigation of a possible viral etiology of IIM. Studies of quantitative slot blot hybridization with coxsackievirus probes and RNA from IIM muscle biopsies and in situ hybridization of biopsies with a Theiler's virus probe have revealed a few positive hybridizations in each study. Although there are some fundamental problems with these studies, these intriguing results bear confirmation. These results continue to implicate picornaviruses as the primary suspects in the pathogenesis of IIM. HIV has now been associated with a number of rheumatologic syndromes, including a polymyositis that is indistinguishable from IIM, and we can expect additional changes in the epidemiology of this family of disorders in coming years. Study of these patients may provide insight into the etiopathogenesis of IIM.