THE term histiocytosis X was introduced by Lichtenstein to group together the syndromes of eosinophilic granuloma of bone, Hand-Schüller-Christian disease, and Letterer-Siwe disease into a common disease entity expressing different manifestations of reticuloendotheliosis, or histiocytic proliferation of uncertain etiology.1
Eosinophilic granuloma is the localized variety of histiocytosis X manifested by single or multiple isolated bony lesions, and carries a favorable prognosis. The Hand-Schüller-Christian variety is the more chronic protean manifestation with multiple bony and soft tissue involvement, and carries a prognosis less favorable than eosinophilic granuloma. Acute progressive histiocytosis, first described by Letterer,2 further defined by Siwe3,4 and subsequently termed Letterer-Siwe disease by Abt and Denenholz5 is the aggressive form of histiocytosis X and assumes the most grave prognosis.
Tos6 has recently reviewed the otolaryngological manifestations in Letterer-Siwe disease, essentially as follows. This variety of histiocytosis X occurs in young children generally under 4 years
Cohn AM, Sataloff J, Lindsay JR. Histiocytosis X (Letterer-Siwe Disease) With Involvement of the Inner Ear. Arch Otolaryngol. 1970;91(1):24–29. doi:10.1001/archotol.1970.00770040050007