Clinical, biochemical and histological responses to treatment in polymyositis: a prospective study.

Routine methods of monitoring treatment responses in polymyositis patients, such as clinical strength assessments and measurements of ESR and serum creatine kinase, have been compared with functional strength measurements and assay of serum myoglobin levels, in a prospective study of nine cases followed for up to five years. Seven patients also underwent serial muscle biopsies during the first year of treatment in order to document the nature and chronology of histological changes during therapy. Inflammatory and necrobiotic changes indicating active myositis resolved within six months in all cases and no patient developed histological evidence of steroid myopathy. Scores on functional muscle strength assessments improved more slowly than static manual muscle strength test results, reflecting morphometric and architectural abnormalities in the biopsies which persisted throughout the period of observation. Serum creatine kinase levels returned to normal more rapidly than serum myoglobin. No statistical relationship was found between muscle strength measurements and biochemical or histological changes within the patients as a group, but variations in these indices in individual subjects reflected changes in clinical state.