Granulomatosis with polyangiitis in a patient with biopsy-proven IgG4-related pulmonary disease and coincident small cell lung cancer

Granulomatosis with polyangiitis (GPA) was diagnosed in a patient with a 16-month history of IgG4-related lung disease that spontaneously became asymptomatic. Cytoplasmic antineutrophil cytoplasmic antibody (ANCA) was positive at the time of diagnosis of IgG4-related disease (IgG4-RD), but there was no vasculitis or kidney disease. Sixteen months later he developed rapidly progressive glomerulonephritis that responded to cyclophosphamide...