Background/Purpose

Comorbidity in patients with Rheumatoid Arthritis (RA) is highly prevalent and plays an important role in determining RA related outcomes. Several studies have reported the negative association of comorbidity with functioning in general. The information about the association of specific comorbidities with functioning in patients with RA is limited. Evaluating specific comorbidities will provide valuable information for clinical practice and the management of patients with RA.      

The aim of this study was to investigate the long term association of a wide range of specific comorbidities with physical and mental functioning in patients with RA.

Methods

Longitudinal data over a period of 11 years were collected from 882 patients with RA at study inclusion. Somatic comorbidity was measured at baseline, with a questionnaire including 20 chronic diseases, from which 9 categories of chronic somatic comorbidity were created. Comorbid depression was measured at baseline, with the Center for Epidemiologic Depression Scale. Physical functioning was measured with the Health Assessment Questionnaire (HAQ) and with the physical component summary of the Short Form 36 health survey (SF-36). Mental functioning was measured with the mental component summary of the SF-36. To determine the impact of specific comorbid conditions on functioning and on change in functioning we performed a longitudinal analysis.

Results

The mean age of the patients at was 59.3 (SD 14.8) years, 72% of the patients were women, their median disease duration was 5.0 (IQR 2.0-14.0) years, and 68% had ≥ 1 comorbid condition. The mean HAQ score for an average patient was 0.98 on average over the 11-years follow-up period. Circulatory conditions (mean HAQ score + 0.28) and depression (+0.38) were associated (p<.05) with low physical functioning according to the HAQ. An average patient with a circulatory condition had a mean HAQ score of 0.98 + 0.28 = 1.46. Circulatory (mean SF-36 score - 3.23), respiratory (-2.74), musculoskeletal conditions (-2.85), cancer (-5.26) and depression (-3.36) were associated  (p<.05) with low physical functioning according to the SF-36, while respiratory conditions (-2.28) and depression (-12.81) were associated (p<.05) with low mental functioning. The improvement in physical functioning according to the HAQ was 0.01 annually for an average patient. Genitourinary conditions were associated with a decline in physical functioning over time (p<.05). An average patient with a genitourinary condition declined in physical functioning with 0.01 – 0.04 = -0.03 annually. Digestive conditions were associated (p<0.05) with a decline in mental functioning.

Conclusion

Patients with specific comorbid conditions have an increased risk of low or declining functioning on the long term. Targeted attention for these specific comorbid conditions by clinicians and general practitioners is important. Diagnostics during the course of the disease, adequate referral to and working together with other specialists might improve physical and mental functioning in patients with RA.