Necrotizing alveolar capillaritis in autopsy cases of microscopic polyangiitis. Incidence, histopathogenesis, and relationship with systemic vasculitis.
OBJECTIVE
To determine the incidence of necrotizing alveolar capillaritis, to elucidate its histopathogenesis and the most reliable histopathologic features for its detection, and to explore its relationship with systemic vasculitis in microscopic polyangiitis.


METHODS
Twenty-five autopsy cases of microscopic polyangiitis were examined. Double staining with periodic acid-silver methenamine and trichrome was used.


RESULTS
Periodic acid-silver methenamine and trichrome staining proved to be a useful and convenient method for the detection of necrotizing alveolar capillaritis. Capillaritis was detected in 10 (40%) of the 25 cases studied. Of 18 cases that exhibited the early degenerative stage of systemic vasculitis, capillaritis was seen in 10 (56%). Fibrinoid necrosis of the alveolar wall was the most reliable histopathologic feature for detecting necrotizing alveolar capillaritis in microscopic polyangiitis. The early stage of capillaritis displayed very little neutrophil exudation, and conspicuous accumulation of neutrophils developed after fibrinoid necrosis. Statistical analysis revealed that alveolar capillaritis had a statistically significant correlation (P < .05) with necrotizing vasculitis of the pulmonary circulatory system. Capillaritis tended to occur when systemic vasculitis of microscopic polyangiitis was in its early degenerative stage.


CONCLUSIONS
Necrotizing alveolar capillaritis was detected in about half of the microscopic polyangiitis autopsy cases that exhibited the early degenerative stage of systemic vasculitis, and results based on earlier reports of clinical observations may have been too conservative.
Akikusa
B
B
Department of Pathology, School of Medicine, Chiba University, Japan.
Sato
T
T
Ogawa
M
M
Ueda
S
S
Kondo
Y
Y
D000328:Adult; D000368:Aged; D001344:Autopsy; D002196:Capillaries; D005260:Female; D006470:Hemorrhage; D006801:Humans; D007150:Immunohistochemistry; D008171:Lung Diseases / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D009336:Necrosis; D009504:Neutrophils; D010488:Polyarteritis Nodosa / Q000276:immunology / Q000473:pathology*; D011650:Pulmonary Alveoli / Q000098:blood supply* / Q000473:pathology; D013194:Staining and Labeling; D014657:Vasculitis / Q000276:immunology / Q000473:pathology*