SAT-520 Massive Thyroid Enlargement due to Langerhans Cell Histiocytosis

Abstract M. Barbera: None. M. Fasen: None. H.M. Lawler: None. M.T. McDermott: None. A.M. Elsheikh: None. Massive Thyroid Enlargement due to Langerhans Cell Histiocytosis Introduction: Langerhans cell histiocytosis (LCH) is a multisystem disease with diabetes insipidus (DI) being the most common initial manifestation. However, this case demonstrates a rare presentation of a massive goiter from LCH involvement of the thyroid gland causing respiratory distress which rapidly improved following treatment with trametinib. Clinical Case: A 27-year-old male presented with large central neck mass, stridor, dysphagia, night sweats, and dysphonia. Initial laboratory evaluation showed TSH 4.94 uIU/ML, with a free T4 of 0.64 ng/dL. Neck CT revealed diffuse enlargement of the thyroid gland with mass effect and lymphadenopathy. PET showed hypermetabolic thyroid gland which extended to the superior mediastinum and low level associated FDG uptake of bibasilar lung nodules. Biopsy of the thyroid mass resulted with lesional histiocytes with elongated, grooved nuclei, with intermixed eosinophils, CD207 (langerin) and CD1a-positive histiocytes in lesional tissues by immunohistochemistry consistent with LCH. Genetic testing was positive for BRAF mutation, exon 12, N486_P490 deletion. He was readmitted due to airway compromise and hypophysitis resulting in diabetes insipidus (DI), adrenal insufficiency (AI), hypogonadism, and hypothyroidism. He was initially treated with 10 mg of IV dexamethasone with minimal improvement, then transitioned to trametinib 2 mg daily resulting in rapid improvement of symptoms and thyroid size. Trametinib treatment was complicated by hyponatremia, skin lesions, and GI bleed for which treatment was held then decreased to 0.5 mg every other day. Repeat CT neck five months after treatment initiation showed complete resolution of thyroid enlargement and lymphadenopathy. Clinical lessons: Rarely, LCH presents with direct involvement of the thyroid gland making diagnosis difficult. This is further complicated by pathologic features that can be mistaken for papillary thyroid cancer and cooccurrence of other thyroid disorders. Given these challenges, it is necessary to consider LCH as a cause of thyroid goiter especially if the patient presents with DI and AI to prevent delay in diagnosis. This is particularly important when targeted therapy can be offered as in this case where trametinib resulted in rapid improvement of airway compromise. Reference:(1) Makras, P, Alexandraki, K, Chrousos, G, Grossman, A, and Kaltsas, G. Endocrine Manifestations in Langerhans cell histiocytosis. Trends in endocrinology and Metabolism. Vol 18 No. 6 (2) Mi, B, Wu, B, Fan, Y, Ka Seng Thong, B, Chen, Y, Wang, X, and Wang, C. Thyroid Langerhans cellhistiocytosis concurrent with papillary thyroid carcinoma: A case report and literature review. Frontiers in Medicine. DOI 10.3389/fmed.2022.1105152 Saturday, June 1, 2024