TORONTO, Canada—In rheumatoid arthritis (RA), inflammation is thought to be the major determinant of disability in early stage disease, with joint damage the major determinant in later RA. However, in psoriatic arthritis (PsA) the influence of disease activity on function (measured by Health Assessment Questionnaire (HAQ) scores) tends to decline with disease duration, but there is less evidence that the impact of joint damage on functional ability increases over the course of illness, according to a new study in the March issue of Arthritis & Rheumatism.¹

"Rheumatologists need to know that there is a relationship between active inflammation and impaired function in psoriatic arthritis. Thus, patients with active inflammation need to be treated appropriately if function is to be preserved," contributing study author Dafna D. Gladman, MD, FRCPC, professor of medicine at the University of Toronto, in Ontario, Canada, told CIAOMed. "Moreover, there is a relationship between joint damage and impaired function."

The latter, however, is not as important with prolonged disease, Gladman stressed. "This is likely due to the fact that patients adapt to the presence of deformities as long as there is no pain related to inflammation."

Physical function, disease activity, and joint damage affect HAQ disability

Dr. Gladman et al studied 382 patients who attended a psoriatic arthritis clinic between June 1993 and March 2005 and who had completed two or more HAQs per year. The researchers also assessed clinical and laboratory measures of disease activity and damage including erythrocyte sedimentation rate (ESR) and x-rays of the hands, feet, spine, and sacroiliac joints at the time of each HAQ assessment. They investigated the longitudinal relationship between disease activity, damage, and HAQ score.

The number of actively inflamed joints (measure of disease activity) and the number of clinically deformed joints (measure of damage) were positively and significantly related to the HAQ score, the study showed. The interaction term for illness duration and number of actively inflamed joints was statistically significant, with or without inclusion of the ESR rate and morning stiffness (P <.001 and P = .029, respectively). The positive effects of actively inflamed joints on the level of the HAQ score decreased over increasing duration of PsA.

An increase of one actively inflamed joint increased the odds of disability (a nonzero HAQ score) by 20% (if ESR and morning stiffness are considered) or 30% (not considering ESR and morning stiffness). An increase of one clinically deformed joint increased the odds of disability by only 4.4% or 3.8%, using the same analytical models. Similarly, an increase of 10 inflamed joints raised the HAQ score by .170 or .193, but an increase of 10 clinically deformed joints raised the HAQ score by an estimated .099 or .097.

The researchers suggest that this might reflect PsA patients' ability, over the long duration of the disease, to cope with or compensate for clinically deformed joints. They note, "there was no evidence to suggest that joint damage was the major determinant of HAQ score in late disease."

"Rheumatologists must follow patients with psoriatic arthritis carefully and assess them for the presence of disease activity and damage. This includes the assessment of actively inflamed and clinically and radiologically damaged joints," Gladman told CIAOMed. "Rheumatologists should treat patients with appropriate medications to prevent persistent inflammation and ensuing joint damage."

Reference

1. Husted JA, Tom BD, Farewell VT, et al. A longitudinal  study of the effect of disease activity and clinical damage on physical function over the course of psoriatic arthritis. Does the effect change over time? Arthritis Rheum. 2007;56:840-849.