SUN-609 Diagnosis of Diffuse Sclerosing Variant of Papillary Thyroid Cancer Confounded by Concurrent Postpartum Thyroiditis

Background: Diffuse sclerosing variant (DSV) is a rare and aggressive subtype of papillary thyroid carcinoma (PTC) that affects younger patients and has the sonographic features of a diffusely enlarged thyroid gland with heterogeneous echotexture and scattered microcalcifications, with or without an identifiable nodule, increased vascularity or regional lymphadenopathy (1). Clinical Case: A post-partum 25-year-old female with history of IV drug use was evaluated for thyromegaly and thyrotoxicosis. She was initially found to have generalized thyroid enlargement on exam six weeks after delivery. At that time she was asymptomatic. Thyroid function tests revealed TSH <0.01 uIU/mL (ref 0.47 - 4.68), free T4 3.47 ng/dL (ref 0.78 - 2.19), and free T3 10.2 pg/mL (ref 2.3 - 4.2). TPO antibodies were negative. Six weeks later, she developed anterior neck pain. Exam revealed a persistently enlarged thyroid gland now with tenderness to palpation. Repeat TSH was <0.01 uIU/mL. Neck ultrasound showed an enlarged thyroid gland with diffusely abnormal echotexture with suggestion of extensive microcalcifications. Color Doppler revealed diffuse hyperemia. No discrete nodule was identified. Five enlarged adjacent anterior cervical lymph nodes were identified that contained nodular foci similar to the appearance of the thyroid gland, including microcalcifications. The interpreting radiologist considered the imaging features to be compatible with DSVPTC, and recommended surgical consultation. Endocrinology was asked to evaluate via electronic consultation. Given her hyperthyroidism, anterior neck tenderness, and time course following delivery, her presentation was attributed to post-partum painful thyroiditis with reactive lymph nodes. Infectious thyroiditis was also considered. FNA was not immediately recommended due to lack of a discrete nodule on ultrasound, concern that inflammatory changes associated with active thyroiditis could lead to inaccurate biopsy results, and the fact that thyroid cancer does not typically arise from hyperfunctioning tissue. However after reiteration of concern for PTC by the radiologist, she was referred for FNA. FNA of the right thyroid lobe and one enlarged right level 3 lymph node were positive for PTC. She subsequently underwent total thyroidectomy with bilateral central neck dissection which revealed multifocal, bilateral diffuse DSVPTC without dominant nodule, with lymphatic invasion and focal angioinvasion. 37/94 lymph nodes were involved, with extranodal extension seen. Treatment with RAI is planned. Clinical Lesson(s): DSVPTC has characteristic sonographic features and may not present with a nodule; presence of these features should prompt further investigation even in the setting of an atypical clinical presentation. References: (1) Yun MB, et al. Ultrasonographic Features of DSVPTC. Journal of Medical Ultrasound. 2011; 19:41-46.