Incidence and aetiologies of pulmonary granulomatous inflammation: A decade of experience

Background and objective Granulomatous lung disease (GLD) is caused by a wide range of conditions. Often there is a need to correlate pathological findings with clinical, microbiological or radiological data to determine an aetiology. The aim of this study was to determine the different aetiologies of GLD over the past decade. Methods Among 2228 consecutive lung specimens from 1999 to 2011, 226 cases (10.1%) were positive for GLD. One hundred ninety patients were retrospectively reviewed and diagnoses were assigned based on availability of histological/clinical/microbiological correlation. Results A confident, probable and uncertain diagnosis was made in 68.4%, 13.2% and 18.4% patients. The aetiologies comprised infectious, non-infectious and uncertain in 54.7%, 26.8% and 18.4% patients. Mycobacterial infections constituted 27% of all patients, and included atypical, tuberculous and unclassified mycobacteria in order of frequency. Acid-fast bacilli (AFB) were visualized in tissue sections in 29% cases and cultured in 73% cases. Fungal infections comprised 27% of all cases, which included Coccidioides, Cryptococcus, Aspergillus and Histoplasma in order of frequency. Fungi were visualized in tissue sections with Gomori methenamine silver (GMS) stain in 83% patients and cultured in 52% cases. Sarcoidosis was the major non-infectious aetiology, constituting 21% of all patients. Necrosis in granulomas was associated with the presence of infection (P < 0.001). Conclusions The aetiology in necrotizing GLD with negative AFB and GMS stains is most likely infectious due to atypical mycobacteria. Coccidioidomycosis was the most common fungal infection. The aetiology in non-necrotizing GLD is most likely non-infectious, probably sarcoidosis.