Muscle Infiltrative Adult Multisystem Langerhans Cell Histiocytosis Detected on Fluorodeoxyglucose Positron Emission Tomography/ Computed Tomography - A Rare Case.

Langerhans cell histiocytosis (LCH) is a disease of unknown pathogenesis characterized by the accumulation of Langerhans cells which show immunopositivity for S-100 and CD1a. LCH with skeletal muscle involvement has been rarely described in literature. F-fluorodeoxyglucose positron emission tomography/computed tomography (F-FDG PET/CT) is an important tool in identifying the sites of involvement in LCH. We present a rare case of muscle invasive LCH where F-FDG PET/CT showed involvement of multiple other sites such as the liver, bones, bone marrow, and possibly the thyroid gland in our case. Further, the current case also shows that liver involvement by LCH (possibly fibrotic phase) can be negative on PET but show lesions on CT.