It is characterised by an intramuscular microangiopathy mediated by a complement membrane attack complex. There is a loss of muscle capillaries, muscle ischaemia, muscle-fibre necrosis and perifascicular atrophy. There is an unmistakable rash with purplish appearance on the eyelids, cheeks and light exposed areas. A rash is often seen on the extensor surfaces of knees, elbows and knuckles, and this becomes scaly.
Treatment is usually with steroids, but cytotoxic drugs and immunosuppressants are also added.
Many patients do not respond to this treatment and remain physically disabled. The study from the NIH in Bethesda looked at fifteen patients with therapy resistant dermatomyositis. Patients were block randomised to immune globulin infusion or placebo by disease severity, and they continued on their normal therapy during the study. Treatment was for three months, followed by cross-over after a one month washout. Patients were followed for three months after the end of the study before codes were broken.