LBSAT310 A Rare Disease Engulfing Thyroid And Masquerading As Common Thyroid Disorders

INTRODUCTION: – Langerhans cell histiocytosis (LCH) is a rare clonal disorder caused by the CD207+ Langerhans cells derived from the myeloid origin. We present a case of LCH where it mimicked Hashimoto's and Riedel's thyroiditis and completely infiltrated the thyroid gland. CASE DESCRIPTION: – A 54-year-old female was initially diagnosed with hypothyroidism, goiter, and bilateral parotid and submandibular glands enlargement. CT imaging revealed a diffuse goiter which imposed infraglottic airway narrowing and a suspicious left inferior thyroid nodule. Biopsy revealed atypia of undetermined significance. GSC showed a 50% suspicion of malignancy with a negative BRAF. Follow up imaging revealed increased infiltrative masses within the salivary glands, enlarging thyroid gland, and increased infiltration of the superior component of the right thyroid lobe into the submandibular space. A core needle biopsy revealed a background of acute and chronic inflammation without evidence of malignancy. Sjogren's, sarcoidosis and IgG4 diseases were ruled out. She was then referred to us after a myriad of work up. She had a diffusely enlarged goiter with a crusted area of skin over the thyroid gland and significant bilateral parotid swelling. We repeated a thyroid ultrasound which revealed diffusely enlarged and heterogeneous thyroid glands with pseudo-nodules and 3 suspicious nodules greater than 1cm on right and left lobes. She also had prominent reactive lymphadenopathy. Her submandibular glands were hypoechoic, avascular, markedly enlarged and abnormal appearing. She underwent total thyroidectomy. Pathology revealed proliferation of histiocytes, few islands of lymphoid tissue, and eosinophilic micro abscesses without any identifiable thyroid parenchyma in the entire resected specimens. Immunohistochemistry confirmed the diagnosis of Langerhans Cell Histiocytosis with atypical features. BRAF (V600E/V600K) mutation was again not detected. Flow cytometry showed no evidence of neoplastic myeloid blast population. She was referred to an oncologist for further management of LCH. DISCUSSION: – Our patient had a remarkably diffuse goiter with a sonographic appearance mimicking Hashimoto's thyroiditis or Riedel's thyroiditis. Initial thyroid FNA failed to reveal LCH. The diagnosis was reached only after total thyroidectomy. Treatment depends on single or multi-system involvement, presence or absence of risk organ involvement, and presence or absence of BRAF mutation. CONCLUSION: In the cases of infiltrated thyroid diseases, Langerhans cell histiocytosis should be on the differential diagnosis, especially if there is concomitant infiltrative process in other organs. The sonographic finding can mimic Hashimoto's or Riedel's thyroiditis which may lead to misdiagnosis and treatment delay. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.