Initial CXR showed reticular interstitial pattern with preserved lung volume. Right knee x-ray revealed femoral and tibial metaphyseal sclerosis. Lung HRCT showed predominantly cystic mid and upper zone disease with interstitial thickening, a few nodules and preservation of lung volumes. Erdheim-Chester Disease (a non-langerhan's cell histiocytosis) was suspected, and the classic symmetrical metaphyseal sclerosis with increased uptake on Tc-MDP bone scan was confirmed when both knees were imaged. The patient died 8 months following symptom onset.