[A case of interstitial pneumonia possibly associated with polyarteritis nodosa].

A 71-year-old man was admitted due to persistent pyrexia of over 2 weeks duration, dry cough, and chest computed tomographic (CT) findings of interstitial pneumonia. On admission, his body temperature was 38.0 degrees C, and there was mild livedo reticularis observed on the trunk and skin of the extremities. Fine crackles were detected in the lower lung fields. Laboratory examinations showed high levels of an inflammatory reaction and a positive rheumatoid factor, but the findings were negative for any other autoantibodies, including the antineutrophil cytoplasmic antibody. His bronchoalveolar lavage fluid revealed an increase in CD4+ lymphocytes. A biopsy specimen of the abdominal skin showed necrotizing vasculitis of the muscular arteries. Lung biopsy specimens showed necrotizing and granulomatous vasculitis of the pulmonary arteries in the usual interstitial pneumonia pattern, with numerous lymphoid follicles. Therefore, a diagnosis of polyarteritis nodosa was clinically and pathologically established. This case of interstitial pneumonia associated with polyarteritis nodosa was difficult to discriminate from microscopic polyarteritis.