An unusual case of adult-onset multi-systemic Langerhans cell histiocytosis with perianal and incident thyroid involvement

Summary Langerhans cell histiocytosis (LCH) is a rare sporadic disease characterized by histiocytic neoplastic infiltration of various organ systems and a wide spectrum of clinical manifestations, ranging from benign and self-limiting to lethal. Herein, we report a rare case of adult-onset multi-systemic LCH in a 36-year-old male patient with an initial perianal presentation and incidental finding of subsequent thyroid gland involvement in the follow-up period. The patient with a history of perianal LCH treated with surgical excision and local radiotherapy was referred to our Endocrinology Department upon detection of hypermetabolic nodular lesions in the left lateral lobe of thyroid gland on positron emission tomography–computed tomography (PET/CT) scan in the nineth month of follow-up. Current evaluation revealed euthyroid status, a hypoechoic solid lesion of 13 × 9 mm in size with irregular borders in the left thyroid lobe on thyroid USG and cytologic assessment of thyroid nodule. The patient was diagnosed with suspected, oncocytic lesion, Hashimoto thyroiditis or LCH. The patient underwent total thyroidectomy and pathological assessment confirmed the diagnosis of Langerhans cell histiocytosis. Assessments in the sixth month of postoperative follow-up revealed euthyroid status with no thyroid tissue remnants or pathological lymph node on thyroid USG. In view of the multifocal lesions indicating multi-system disease, a systemic chemotherapy protocol with combination of prednisone (PRED) and vinblastine (VBL) has been planned by the hematology department. Learning points: Langerhans cell histiocytosis (LCH) shows a wide clinical spectrum and prognosis that ranges from benign and self-limiting single-system disease (with single or multifocal lesions) to a potentially lethal multi-system disease with severe organ dysfunction and death in some cases. It has been stated that the diagnosis is often delayed in perianal LCH unless LCH is specifically considered in the etiology, despite the fact that mucosal involvement may precede systemic involvement. Our findings support the statement that most of patients with LCH were PET positive at the time of initial diagnosis, while also emphasize the inclusion of this imaging modality as a part of the diagnostic workflow as well as in the setting of treatment response evaluation among adult LCH patients.