A rare case of multisystemic Langerhans cell histiocytosis in an adult affecting the thyroid gland, skeletal system, and pituitary gland: A case report.

Langerhans cell histiocytosis (LCH) is a rare disorder affecting usually children and rarely adults. The most common site affected is bone. The involvement of the thyroid gland in LCH is extremely rare and it is usually observed in an adult as a multisystemic disease. Adult males presented with anterior neck swelling, and fine needle aspiration cytology (FNAC) diagnosed it as suspicious for malignancy. On frozen sectioning, differential diagnosis was given as non-Hodgkin lymphoma and poorly differentiated malignancy. On immunohistochemistry (IHC), tumor cells were positive for CD1a and S100p. Thus, the final diagnosis offered was LCH-thyroid. The pathogenesis is unclear and believed to be related to immune dysfunction, cytokine mediators, viral infection, smoking, and genetic factors. Due to its rarity, thyroid LCH is often misinterpreted as other common disorders of the thyroid and results in delayed diagnosis. This case highlights the importance of histomorphology and the use of ancillary techniques such as IHC to arrive at a diagnosis in time and hence the treatment.