Langerhans cells are antigen-presenting dendritic cells in the epidermis. These dendritic cells migrate from the bone marrow to the skin and lymph nodes. In Langerhans cell histiocytosis, these cells undergo clonal proliferation in the bone marrow.
In Langerhans cell histiocytosis, infiltration of histiocytes into the bone marrow affects bone architecture. Lytic lesions are present. Bone lesions known as eosinophilic granulomas are present as both unifocal and multifocal lesions. Lytic lesions usually present as bone pain and pathological fractures.
The skull is the most common bone to be affected by infiltration. The second most commonly affected bones are the long bones of the upper limb.
In multifocal disease, the hypothalamic-pituitary axis is involved and Hand-Schüller-Christian triad is present. Bulging of eyes, diabetes insipidus, and bone breakdown comprises this triad.
The triad of diabetes insipidus, exophthalmos, and lytic bone lesions is known as the Hand-Schüller-Christian triad. Diabetes insipidus presents with polyuria due to decreased ADH Secretion.
In multifocal disease, scaly erythematous lesions and red papules can be present and are more pronounced in intertriginous areas. Up to 80% of LCH patients have extensive eruptions on the scalp.
Due to skull involvement, the mastoid process of the temporal bone is also affected. Due to the destruction of the mastoid antral cells, recurrent otitis media is common.
Birbeck granules are collections of rod- or racket-shaped organelles found in Langerhans cells. The exact function of these organelles is not known.
Birbeck granules are often said to have a "tennis racket" appearance with a loop and handle.
S100 is a cytoplasmic protein that is used as a tumor marker on immunohistochemical staining, particularly for cells derived from the neural crest. CD1a is a marker of antigen-presenting cells.
If the disease is unifocal and spares the skull without any major systemic manifestations, the patient is kept under observation.
If the patient has skull involvement, multiple bone lesions, or systemic manifestations, immunosuppression with prednisone is initiated. Bone lesions are excised. Chemotherapy with vinblastine is added in systemic disease. Pituitary hormone replacement is also indicated.
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