Letterer–Siwe disease
（重定向自Reticulosis）
Letterer–Siwe disease is an old name for Langerhans cell histiocytosis (LCH), from a time when LCH was thought to be several different diseases; Letterer–Siwe disease, Hand-Schuller-Christian disease, Eosinophilic granuloma and Hashimoto-Pritzker disease. Later they were all put together under the name Histiocytosis X. The X was found to be the Langerhans cell, a dendritic white blood cell. LCH is not believed to be genetic, even though there have been a few reports of more than one person affected by LCH within the same family. Still to this day, the cause is unknown, after researchers have worked very hard on trying to figure it out for decades.