Antineutrophil cytoplasmic antibodies in patients with pulmonary tuberculosis

Mycobacterium tuberculosis is a major cause of mortality and morbidity worldwide. Infection with this bacterium is known to induce the development of autoantibodies of which a few are also known to be diagnostic markers for some other diseases. Antineutrophil Cytoplasmic Antibodies (ANCA's) are among those autoantibodies used in clinical setting for diagnosing systemic vasculitic syndromes. Multiple studies investigated ANCA positivity in diseases other than small vessel vasculitis.

This study was performed to determine the prevalence of ANCA in pulmonary tuberculosis (TB) which may lead to the false diagnosis of Wegener's granulomatosis (WG) or vice versa.

In a case-control study, 32 consecutive smear positive pulmonary TB patients and 32 normal individuals were studied. All cases and controls were screened for ANCA by indirect immunofluorescent assay (IIF), and MPO and PR3 were also tested by ELISA.

A prenuclear pattern (P-ANCA) was detected in 25% of the cases and 6.25% of the controls and a cytoplasmic pattern (C-ANCA) was deserved in 3.1% of both the cases and the controls by IIF assay. ANCA specificities tested by ELISA in cases revealed that 75% of the cases had anti-MPO and 12.5% had anti-PR3, while in the in controls, 3.12% had anti-MPO and none had anti-PR3. The positive ANCA significantly correlated with TB (p<0.01).

ANCA's may be observed in both TB and systemic vasculitic syndromes such as WG. Tuberculosis and WG share some clinical features. Therefore, in countries with a high prevalence of TB, one has to distinguish between these two diseases especially when no sign of extrapulmonary involvement is observed.