Problems in the assessment of disease activity in ankylosing spondylitis.

Serial assessments of disease activity using clinical, laboratory and thermographic indices were made on 20 patients with ankylosing spondylitis (AS) before and after active in-patient exercise classes and two months after discharge. Clinical measurements and the erythrocyte sedimentation rate suggested decreased activity by the time of the final assessment but plasma viscosity and thermography suggested increased activity and levels of C-reactive protein were unchanged. Functional improvements occurred mostly during the in-patient period. A wide range of complement levels was found but did not change, and IgG rheumatoid factor levels were negative throughout. The problems of laboratory assessment in AS are stressed.