To describe the incidence and characteristics of the infection caused by Mycobacterium tuberculosis in patients with autoimmune diseases.
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.
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.
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.