The histiocytic disorders are clinically heterogeneous disorders that result from an abnormal proliferation of histiocytes that are either
Classifying histiocytic disorders is difficult (see table Histiocytic Disorders) and has changed over time as an understanding of the biology of these cells has evolved. Langerhans cell histiocytosis is the most common histiocytic disorder. There are other rare histiocytic disorders such as Erdheim-Chester disease and juvenile xanthogranuloma, some of which are now considered variants of Langerhans cell histiocytosis.