Microscopic polyangiitis presenting as a "pulmonary-muscle" syndrome: is subclinical alveolar hemorrhage the mechanism of pulmonary fibrosis?

Microscopic polyangiitis (MPA) may present with a syndrome that resembles idiopathic pulmonary fibrosis (IPF). We describe an MPA patient with the clinical presentation of a "pulmonary-muscle" syndrome in which interstitial lung disease antedated the onset of myopathy. Identification of vasculitis on muscle biopsy was instrumental in recognizing clinical, radiographic, and histopathologic features that were more characteristic of MPA than of IPF. Institution of glucocorticoid and cyclophosphamide therapy led to the induction of a complete remission. The histologic findings in this case implicate subclinical episodes of alveolar hemorrhage as the mechanism of interstitial lung disease in MPA.