An Unusual Cause Of Alveolar Accumulation Of Foamy Macrophages In Adults

A 33-year-old non-smoking female presented with a 6-months history of mild dyspnea and cough. Physiologic testing showed a moderate restrictive ventilatory impairment, whereas high-resolution CT revealed bilateral ground-glass opacities and thickening of interlobular septa. A videothoracoscopic biopsy was performed. Microscopically, the pulmonary architecture was preserved, with only a minimal interstitial fibrosis. The alveolar and the bronchiolar spaces were filled by finely vacuolated macrophages, whereas Pas-positive macrophages expanded the pleural and the interlobular connective tissues. The bronchiolar epithelium had a peculiar clear cytoplasm. Three months after the biopsy, the patient presented with abdominal pain, hepatosplenomegaly and thrombocytopenia. A bone marrow biopsy showed a “sea-blue histiocytosis”. The sphingomyelinase activity, evaluated in cultured fibroblasts, was markedly reduced and a diagnosis of Niemann-Pick disease type B was performed. In the lung: 1) the evaluation of both morphology and localization of the macrophages may provide useful diagnostic clues to the pathologist; 2) although rare, the possibility of a metabolic disease must be considered also in adults; and 3) a diffuse alveolar accumulation of foamy macrophages without a significant fibrosis/inflammation, particularly when associated with a clarification of the bronchiolar epithelium, is characteristic of pulmonary involvement in Niemann-Pick disease.