12398 Isolated Thyroid Gland Langerhans Cell Histiocytosis In A Patient With Simple Goiter

Abstract Disclosure: A.P. Ziganshina: None. G.G. Callender: None. K. Coppola: None. N.M. Druar: None. J. Jacob: None. Background: Langerhans cell histiocytosis (LHC) is an overproduction of white blood cells - histocytes (Langerhans cells) - that accumulate in various organs, forming granulomas and affecting their function. It is a rare entity that can be systemic or confined to an isolated organ only. The thyroid gland is very infrequently a site for isolated LHC penetrance or part of multisystemic disease. Here we present a case of an incidental finding of an isolated LCH of the thyroid gland in a patient with simple goiter. Case presentation: This is a 42-year-old woman who is a chronic smoker with a history of primary hypothyroidism on thyroid replacement therapy, infertility, antiphospholipid antibody syndrome, MTFHR-mutated homocystinemia. She had a long-standing history of intermittent dysphagia and neck discomfort and was noted to have simple goiter measuring 8.9 x 2.8 x 2.8 cm in the right lobe and 7.3 x 2.6 x 2.2 cm in the left lobe. The patient was referred for a total thyroidectomy to relieve compressive symptoms. She had an uncomplicated operation; intraoperatively she was noted to have no suspicious central neck lymphadenopathy or other unexpected findings. The final pathology report demonstrated aggregates of Langerhans cells and eosinophils in a background of lymphocytic thyroiditis. Follow-up cytogenetics performed on the thyroid tissue found an activating (gain of function) mutation in MAP2K1 at codon 57, exon 2, with 7% allele frequency (MAP2K1 K57E). These findings support the diagnosis of LCH. There are no other sites of LCH on PET full body imaging. The patient continues on thyroid replacement therapy and will be closely monitored for PET evidence of systemic involvement of LCH. Conclusion: This clinical case raises awareness of the entity of LCH of the thyroid gland in patients presenting with simple goiter. It is important to differentiate LCH from a simple goiter because it can recur and requires prolonged follow up. Additionally, isolated thyroid LCH can precede or reveal disseminated disease; thus, whole-body surveillance is needed. Presentation: 6/1/2024