Outcome measures of disease activity for rare autoimmune rheumatic diseases.

Systemic lupus erythematosus, scleroderma, myositis and Sjögren's syndrome are rare, complex, multi-systemic rheumatic diseases associated with significant morbidity and mortality. Thorough assessments of disease activity are required to guide clinical management and assess response to new therapies in clinical trials. This article reviews the commonly used outcome measures to assess this group of diseases and discusses the limitations of their use.