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The incidence and clinical characteristics of Mycobacterium tuberculosis infection among systemic lupus erythematosus and rheumatoid arthritis patients in Korea

J.-E. Yun, S.-W. Lee, T.-H. Kim, J.-B. Jun, S. Jung, S.-C. Bae, T.-Y. Kim,
D.-H. Yoo

The Hospital for Rheumatic Diseases, Department of Internal Medicine, Hanyang University College of Medicine, Seoul, South Korea

ABSTRACT
Objectives
The aim of this study was to describe the incidence and clinical characteristics of Mycobacterium tuberculosis infection in SLE and RA patients in Korea where the prevalence rate of active pulmonary tuberculosis in a general population is relatively higher than in Western countries.

Patients
We reviewed the medical records of 283 SLE and 284 RA patients retrospectively and then assessed the incidence, risk factors, and clinical characteristics of active tuberculous infection. We then compared the results for the two different groups.

Results
Tuberculosis was documented in 15 SLE and 7 RA patients with an incidence rate of 7.9/1,000 patient-years and 2.3/1,000 patient-years, respectively (p = 0.003). SLE-associated tuberculosis cases included 3 of miliary tuberculosis, 7 of pulmonary tuberculosis (including 1 case of diffuse pulmonary involvement with meningitis) predominantly involving two or more lobes at the mid-/lower lung field, and 5 extra-pulmonary forms (joint, bone, kidney, larynx, pleura). All of the RA-associated tuberculosis cases were pulmonary forms with the majority being localized to single lobe, and only one case had a past history of tuberculosis, whereas a past history of tuberculosis and a longer duration of the underlying disease were significantly correlated with the development of tuberculosis in the SLE patients. Major organ involvement, the mean daily dosage of prednisolone, and a history of over 30 mg of daily prednisolone were not related to the development of tuberculosis. However, when we took only those patients taking corticosteroid until the diagnosis of tuberculosis for analysis, SLE patients with tuberculosis showed a higher daily dosage of prednisolone than those without tuberculosis.

Conclusion
Taken together, the characteristics of tuberculosis in SLE patients were: (1) a higher incidence rate, (2) more frequent extra-pulmonary involvement, (3) more extensive pulmonary involvement, and (4) a higher relapse rate than in rheumatoid arthritis. Thus, the contributory role of M. tuberculosis infection in the morbidity and mortality of patients with SLE must be emphasized, especially in areas in which this bacteria is endemic.

Key words
Systemic lupus erythematosus, rheumatoid arthritis, Mycobacterium tuberculosis infection.

This work was supported by the research fund of Hanyang University (HY-2000).
Please address correspondence and reprint requests to: Dae-Hyun Yoo, MD, PhD, The Hospital for Rheumatic Diseases, Hanyang University, Seoul, 133-792, South Korea. E-mail: dhyoo@hanyang.ac.kr