Early interstitial lung disease in microscopic polyangiitis: Case report and literature review.

Microscopic polyangiitis (MPA) is a systemic disease included in the Chapel Hill 2012 Classification as necrotizing vasculitis affecting capillaries, venules and arterioles. It usually expresses antineutrophil cytoplasmic antibodies (ANCA) and has a perinuclear immunofluorescence pattern and correlation with anti-myeloperoxidase (MPO) antibodies. Capillaritis with alveolar hemorrhage is the most common manifestation of lung disease. Interstitial lung disease (ILD) is uncommon, with usual interstitial pneumonia being the predominant pattern. However, other patterns such as organizing pneumonia have been described. No guidelines exist for treating patients with ILD and, currently, ANCA-associated vasculitis (AAV) is managed along the lines of small vessel vasculitis. The prognosis with this association is uncertain, with possibilities of relapse and a fatal outcome. We present a case in which ILD was the first manifestation of MPA, without alveolar hemorrhage, with subsequent renal involvement and, in which, the established treatment produced a significant clinical improvement.