musculoskeletal and connective tissue disorders
Granulomatosis with Polyangiitis (GPA)
Pathophysiology of GPA
Characteristically, granulomas form with histiocytic epithelioid cells and often with giant cells. Plasma cells, lymphocytes, neutrophils, and eosinophils are present. Inflammation affects tissues as well as vessels; vasculitis may be a small or large component of the disease. Micronecrosis, usually with neutrophils (microabscesses), occurs early. Micronecrosis progresses to macronecrosis. A central area of necrosis (called geographic necrosis) is rimmed by lymphocytes, plasma cells, macrophages, and giant cells. A zone of fibroblastic proliferation with palisading histiocytes may surround the area. Nonspecific chronic inflammation and tissue necrosis occur in the nose. The lungs are most likely to display the full spectrum of histopathologic abnormalities, but diagnostic features are not typically identified on the small tissue samples obtained by transbronchial biopsy. In the kidneys, the most common finding is a pauci-immune crescentic focal glomerulonephritis with necrosis and thrombosis of individual loops or larger segments of the glomerulus. Vasculitic lesions and disseminated granulomas occur only occasionally. 