Letterer-siwe disease --> histiocytosis
a condition marked by the abnormal appearance of histiocytes (macrophages) in the blood. Lipid h., niemann-pick disease. Sinus h., a disorder of the lymph nodes in which the distended sinuses are completely or nearly completely, filled by histiocytes, as a result of active multiplication of the littoral cells. H. X, a generic term embracing eosinophilic granuloma, letterer-siwe disease and hand-schuller-christian disease and indicating a shared common origin for the three entities.