Tuberculosis prophylaxis in patients with steroid treatment and systemic rheumatic diseases. A case-control study

Objective The aim of this study was to assess the impact of isoniazid prophylaxis in patients with systemic rheumatic diseases who attended a teaching hospital in Mexico City between 1987 and 1992. Methods In this case-control study, patients with systemic rheumatic diseases and t uberculosis (cases) were compared with patients with systemic rheumatic dis eases without tuberculosis (controls). The groups were matched by year of h ospital admission and rheumatic disease. Clinical charts were reviewed for: 1) isoniazid prophylaxis, defined as the administration of isoniazid 300 m g/day for 6 or more months in patients with exposure to steroids (prophylax is with isoniazid was defined as complete, incomplete or any prophylaxis); 2) exposure to steroids: defined as the administration of prednisone > 15 m g/day (or its equivalent of another steroid) for 3 or more months before tu berculosis or recruitment into the study; 3) exposure to immunosuppressants , defined as the administration of any dose of azathioprine, methotrexate, cyclophosphamide, and/or 6-mercaptopurine, before tuberculosis in the cases or recruitment date in the controls; 4) reactivity to PPD; and 5) other re levant variables. Results Twenty cases and 66 controls were studied. A 70% decrease in the risk of de veloping tuberculosis was found among patients who received any prophylaxis with isoniazid as compared to controls: OR 0.31, 95% CI 0.09 - 0.98, p = 0 .03. A 97% decrease was seen in those patients who received complete prophy laxis: OR 0.034 95% CI 0.0001 - 0.216 p < 0.0001. The protective effect of complete prophylaxis persisted even after controlling for other potential c onfounders, such as age, gender, rheumatic disease, duration of rheumatic s ymptoms, and exposure to steroids and/or immunosuppressants. Conclusion The results of this study suggest that in countries with a high prevalence of tuberculosis the use of isoniazid (300 mg/day for 6 months) in rheumatic patients with exposure to prednisone (> 15 mg/day for three or more months ) may be useful to prevent tuberculosis, independently of the results of th e PPD reactivity test. However, a controlled clinical trial will be require d to confirm these results.