Crystal-storing histiocytosis as a cause of symptomatic cardiac mass.

Abstract Crystal-storing histiocytosis is a rare disorder that is typically associated with low-grade B-cell lymphomas and monoclonal gammopathy. We present a 64-year-old man with a prior history of weakness and weight loss and hematologic evaluation that had revealed immunoglobulin G κ monoclonal light chains in the serum and negative bone marrow biopsy. He presented with supraventricular tachyarrhythmia and a right atrial mass seen on echocardiogram and excised surgically. Histologically, the tumor was composed of sheets of macrophages infiltrating the atrial myocardium. The histiocytes were filled with multiple needle-shaped, periodic acid-Schiff–negative crystals. These cells and associated plasma cells failed to show clonal light chain restriction by in situ hybridization or immunohistochemistry, and there was no area of lymphoma in the tumor. Ultrastructural examination showed numerous sticklike, trapezoidal, or polygonal dense crystals in the cytoplasm of histiocytes corroborating the diagnosis of ...