<unk>  is a form of histiocytosis which mostly occurs in people with monoclonal gammopathies. Histiocytosis is an excessive number of histiocytes (an immune cell type which is part of the mononuclear phagocyte system). In the vast majority of<unk>  cases (over 90%), immunoglobulins accumulate within the cytoplasm of histiocytes ; in rare cases clofazimine, cystine, silica, or Charcot–Leyden<unk> s may be found in the histiocytes instead. Non-immunoglobulin<unk>  is mostly associated with non-malignant disorders, such as chronic inflammation or autoimmune abnormality conditions such as rheumatoid arthritis, Crohn's disease, or Helicobacter pylori gastritis. It may be a localised or generalised disease. Examples of locations where histiocytosis may occur include the lungs, pleura, stomach, kidney, bone marrow, thyroid, thymus, and parotid gland. The disease is described as generalised if two or more unrelated sites are involved.
Crystal-storing histiocytosis
Sea-blue histiocytosis
X-type histiocytosis
Langerhans cell histiocytosis
Non-Langerhans cell histiocytosis
Non-X histiocytosis
Malignant histiocytosis
Progressive nodular histiocytosis