“…These three terms are used to point out the differences, which may occur in the clinical picture, in the activity and also the prognosis of this disease. They may best be regarded as being, respectively, the acute disseminated, the chronic progressive, and the benign localized form of histiocytosis X [2,12]. On the other hand, the nosologic entity of these three syndromes is stressed by the fact that different types of transitional forms between Abt-Letterer-Siwe disease, Hand-Schiiller-Christian disease and eosinophilic granuloma of the bone are not uncommon [3,4,12].…”