Incidence and characteristics of tuberculosis in patients with autoimmune rheumatic diseases

OBJECTIVE: To describe the incidence and characteristics of the infection caused by Mycobacterium tuberculosis in patients with autoimmune diseases. PATIENTS AND METHODS: Searching in the database of the department at our institution, all new cases of tuberculosis from 1991 to 2000 were identified in patients with autoimmune diseases; the total follow-up time was calculated as the difference between first and last visits. Time with immunosuppressive drug therapy was obtained for patients with rheumatoid arthritis from a database oriented to the longitudinal follow-up of these patients. The incidence density was calculated as the quotient between the absolute frequency of cases and the sum of individual periods at risk for each subgroup. RESULTS: Fifteen cases of tuberculosis were identified from 3,634 risk patients followed for an accumulated period of 9,795 years (overall incidence 153 per 100,000 patients-year). Fourteen patients were receiving disease-modifying drugs and eleven were receiving corticosteroids at diagnosis. The location of tuberculosis infection was the lung for 33.3% of cases. The incidence by drugs in patients with rheumatoid arthritis was 143 per 100,000 patients-year with methotrexate, 2,703 per 100,000 patients-year with azathioprin, 7,692 per 1,000 patients-year with cyclophosphamide, and 4,878 per 100,000 patients-year for anti-TNFalpha. CONCLUSIONS: Compared with the general population, the incidence density of tuberculosis is increasing in our population, with a higher frequency of extrapulmonary involvement. The incidence density is variable among patients with rheumatoid arthritis depending upon the used drugs.