Objective: To determine the prevalence of antineutrophil cytoplasmic antibodies (ANCA) in patients with diseases that may mimic systemic vasculitides, such as severe multiorgan dysfunction (MOD) and parenchymal pulmonary disorders.
Methods: We conducted a prospective study of patients with MOD admitted to the medical intensive care unit and patients with various lung diseases seen at the outpatient pulmonary clinic of a tertiary care hospital. Patients with a documented diagnosis of Wegener's granulomatosis (WG) served as positive controls. ANCA were determined in serum samples from each patient by a combination of indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assays (ELISAs) for antibodies to proteinase-3 and myeloperoxidase (anti-MPO).
Results: Ninety-nine patients with MOD, 29 outpatients with various lung disorders, and 18 patients with WG were included in the study. ANCA were detected by IIF alone in 16% (15/96) of patients with nonvasculitic MOD and 17% (5/29) of outpatients with various pulmonary disorders. The majority of the positive IIF specimens from each group displayed an atypical IIF pattern (73% and 80%, respectively). Only 1 specimen from patients with nonvasculitic disorders was positive for anti-MPO. ANCA by both IIF and ELISA were detected in 78% (12/14) of control patients with WG.
Conclusion: Detection of ANCA by the combination of IIF and antigen-specific assays for proteinase 3 and myeloperoxidase in diseases that mimic systemic vasculitides is highly specific for WG, microscopic polyangiitis, and Churg-Strauss syndrome.