A CASE CONTROL STUDY OF FOOT ULCERATION IN RHEUMATOID ARTHRITIS PATIENTS

Background: Neuropathy, peripheral vascular disease and foot deformities are known risk factors for the onset of foot ulceration in diabetes [1]. Whilst foot ulcers occur frequently in rheumatoid arthritis (RA), the factors that influence risk in this client group are unknown.Objectives: To test the relationship between identified risk factors for foot ulceration and foot ulcers occurring in a sample of RA patients using a case control approach.Methods: The cases were 15 RA patients reporting foot ulceration in response to a postal survey of patients sampled from a diagnostic register in secondary care (n=1130). The controls were 66 RA patients randomly sampled from the survey respondents (n=883) after matching for age, sex and disease duration. Patients with coexistent diabetes were excluded. Clinical examination included the following: sensation (insensitivity to 10g monofilament); ankle-brachial pressure index (ABPI); foot deformity (Platto indices) and plantar pressure (PressureStatTM readings). A 44 joint count, the presence of pre-ulcerative lesions and current steroid therapy were identified through univariate analysis as potential predictors.Results: Step-wise logistic regression analysis showed that abnormal ABPI was the main predictor of foot ulceration, followed by current steroid therapy and the presence of pre-ulcerative lesions. Whilst swollen joint count was a significant predictor of foot ulceration, abnormal sensation, foot deformity and raised plantar pressures were not. The table gives coefficients, Wald statistic and odds ratios for each of the predictor values. The wide confidence intervals for ABPI were due to sparse data, with very few abnormal values, and the results of Exact logistic regression (more accurate where numbers are low/data sparse) found that ABPI was no longer a significant predictor (p = 0.140). The results did not differ substantially for the other variables. The coefficients, Wald statistic and odds ratios for each predictor variable Variable B Wald statistic Adjusted OR 95% C.I. p value Steroid 2.272 8.397 9.70 2.09 - 45.11 .004 ABPI 2.599 4.429 13.45 1.19 - 151.43 .035 Pre ulcerative lesions 2.002 6.086 7.40 1.51 - 36.30 .014 Swollen joint count .222 4.508 1.25 1.02 -1.53 .034 Conclusion: The aetiology of foot ulceration in RA differs from diabetes. In this study, abnormal sensation, foot deformity and raised plantar pressures were not significantly associated with foot ulceration but active disease and current steroid therapy were. The contribution of peripheral vascular disease to risk is unclear and a multi-centre study of incident cases is needed to investigate this further.References: 1. Abbott, C.A., et al., The North-West Diabetes Foot Care Study: incidence of, and risk factors for, new diabetic foot ulceration in a community-based patient cohort. Diabetic Medicine, 2002. 19(5): p. 377-84.Citation: Ann Rheum Dis, volume 66, supplement II, year 2007, page 373Session: RA – other clinical aspects and comorbidity