<unk>  arises from epidermal dendritic cells<unk>  cells), which are normally involved in the process of antigen presentation to lymphocytic cells.<unk>  cells originally arise from the bone marrow, then the cells migrate to other organs such as the skin, lymph nodes, and lungs. The exact pathogenesis of<unk>  is not fully understood. It is thought that<unk>  is the result of either a true neoplastic process or a reactive immune condition. Genes commonly involved in the pathogenesis of<unk>  include BRAF gene and MAP2K1 gene. On gross pathology, scaly erythema, red papules, and extensive eruptions located on the scalp are characteristic finding of<unk> . Characteristic findings of<unk>  on light microscopy may include clusters of dendritic cells with kidney-shaped nucleus and abundant foamy cytoplasm. On electron microscopy<unk>  is characterized by Birbeck granules, which are electron dense, cytoplasmic, tennis racket-like bodies. On immunohistochemistry<unk>  is characterized by positivity to CD1a, S100, and CD207 (langerin).<unk>  is a rare disease that tends to affect children and adolescents. The median age at diagnosis depends on the specific subtype of the disease. The incidence of<unk>  is approximately 5 per 1,000,000 individuals in the United States. Males are more commonly affected with<unk>  than females. The male to female ratio is approximately 2 to 1.<unk>  usually affects Caucasian and Hispanic individuals. African American individuals are less likely to develop<unk> . Common symptoms of<unk>  include bone pain, rash, fever, and failure to thrive.<unk>  patients often appear cachectic. Physical examination of patients with<unk>  is usually remarkable for scaly erythematous lesions located on the scalp and extremities, localized bone tenderness, and hepatosplenomegaly. Observation is recommended for all pediatric patients with an isolated<unk>  skin involvement. Medical therapy is suggested only for symptomatic cutaneous disease that presents with either extensive rash, sever pain, skin ulceration, or bleeding. Medical therapies used for the treatment of isolated skin lesions of<unk>  include topical steroids, nitrogen mustard, and oral thalidomide. Curettage is the mainstay treatment for single skull lesions that involve the frontal, parietal, or occipital bones. The most commonly used systemic chemotherapy regimen for the management of multiple bone lesions is a combination of vinblastine AND prednisone. The standard therapy recommended for<unk>  involving the spleen, liver, or bone marrow (high-risk organs) consists of vinblastine AND prednisone AND 6-mercaptopurine for a 12 month period.
Langerhans cell histiocytosis
Faisalabad histiocytosis
Malignant histiocytosis
Malignant fibrous histiocytoma
Granulocytic sarcoma
B-cell lymphoma
T-cell lymphoma
Mast cell tumor