The predictors of foot ulceration in patients with rheumatoid arthritis: a preliminary investigation

We explored the predictors of foot ulceration in patients with rheumatoid arthritis (RA). The cases were 15 patients with RA reporting foot ulceration in response to a postal survey of patients sampled from a diagnostic register in secondary care (n=1,130). The controls were 66 patients with RA randomly sampled from the survey respondents (n=883) after matching for age, sex and disease duration. Patients with co-existent diabetes were excluded. Clinical examination included the assessment of known risk factors for foot ulceration in diabetes including: neuropathy (insensitivity to 10 g monofilament), peripheral vascular disease (ankle brachial pressure index [ABPI]), foot deformity (Platto indices) and raised plantar pressure (PressureStat (TM) readings). A 44 swollen-joint count, the presence of pre-ulcerative lesions and current steroid therapy were identified through univariate analysis as additional potential predictors in patients with RA. Forward step-wise logistic regression analysis showed that the following variables were significant predictors of ulceration: steroid therapy (OR=9.70, 95%CI=2.09-45.11, p=0.004), abnormal ABPI (OR=13.45, 95%CI=1.19-151.43, p=0.035), the presence of pre-ulcerative lesions (OR=7.40, 95%CI=1.51-36.30, p=0.014) and swollen-joint count (OR=1.25, 95%CI=1.02-1.53, p=0.034). Abnormal sensation, foot deformity and raised plantar pressures were not significant predictors of ulceration. 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 data is sparse and case matching employed) found that ABPI was no longer a significant predictor (p=0.054). The significance of the other predictors did not differ substantially. In this preliminary 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 further investigation is needed in a larger cohort.