Seasonal occurrence of relapses in inflammatory myopathies: a preliminary study.

The seasonal occurrence of relapses was analysed retrospectively in a group of 53 patients with treated dermatomyositis (DM) or polymyositis (PM). In DM, the incidence of both myositic and cutaneous relapses was highest in summer whereas in the PM group relapses was more evenly distributed throughout the seasons but lowest in summer. The present findings suggest that environmental factors such as intercurrent infections and light exposure may be involved in reactivating the disease process and causing relapses in DM but less so in PM. Further prospective studies are needed to assess the role of environmental factors in the initiation and reactivation of the inflammatory myopathies.