Diagnosing Granulomatosis with Polyangiitis (GPA) on Bronchial Airway Biopsy
Yes, granulomatosis with polyangiitis (GPA) can be diagnosed on biopsy of the bronchial airways, though the diagnostic yield is variable and may not always provide definitive confirmation of the disease. 1, 2
Diagnostic Value of Bronchial Biopsies in GPA
Bronchial biopsies can reveal the three key histopathological findings characteristic of GPA: granulomatous inflammation, necrosis, and vasculitis affecting small to medium vessels (capillaries, venules, arterioles, and arteries) 1
The granulomas in GPA are composed of CD4+ and CD8+ T cells, CD28- T cells, histiocytes, CD20+ B lymphocytes, neutrophil granulocytes, macrophages, and multinucleated giant cells surrounding an area of central necrosis 1
Transbronchial biopsies from stenotic portions of the bronchial tree may yield diagnostic findings including granulomas with giant cells, which can lead to a definitive diagnosis of GPA 2
Limitations and Considerations
Bronchial biopsies have lower sensitivity compared to lung or kidney biopsies, with studies showing that only about 12% of transbronchial biopsies of alveolar tissue are positive for GPA 1
Non-renal biopsies (including bronchial biopsies) in GPA patients are diagnostic in only about 39% of cases, with 10.7% being suggestive and 54.8% showing non-specific findings 3
Biopsies may be reported as "consistent with" rather than definitively GPA, as all three criteria (necrosis, granulomatous inflammation, and vasculitis) must be present for a definitive histological diagnosis 1
Multiple biopsies may be necessary to establish the diagnosis, particularly in ANCA-negative patients or those with atypical clinical presentations 3
Optimizing Diagnostic Yield
Careful endoscopically directed biopsy after cleaning and decongesting the area may provide a better yield 1
Open lung biopsies, although more invasive, have been shown to provide higher diagnostic yield with a relatively low risk of complications 1
Abnormal tissue from the sinuses or lungs is likely to provide a better yield than nasal or bronchial biopsies alone 1
Combining biopsy results with ANCA testing increases diagnostic accuracy, as PR3-ANCA is detected in 84-85% of patients with GPA 4
Clinical Context
Bronchial biopsies are particularly valuable in c-ANCA negative, localized GPA patients, where they can have a specificity of 96% and a positive predictive value of 78% 1
When evaluating bronchial biopsies, occasional eosinophils may be present, which can confuse the diagnosis with eosinophilic granulomatosis with polyangiitis (EGPA) 1
The diagnostic approach should include imaging of the lungs to reveal diffuse infiltration, pulmonary nodules (2-4cm in diameter), or large necrotic cavitating granulomatous masses that may guide biopsy sites 1
In cases where bronchial biopsy results are inconclusive, additional biopsies from other affected sites (kidney, lung parenchyma, skin, or nasal mucosa) should be considered 4, 3
While bronchial airway biopsies can diagnose GPA, they should be interpreted in the context of clinical presentation, ANCA status, and imaging findings for optimal diagnostic accuracy.