PSAT293 Uncommon Presentation of Hashimoto Thyroiditis

Hashimoto thyroiditis (HT) is the most common cause of hypothyroidism in developed countries, which presents with diffuse goiter or atrophic gland. Staii et al. reported a 7.4 per cent prevalence of localized HT diagnosed by fine needle aspiration (FNA) cytology in euthyroid patients during thyroid cancer screening. Although, a transient solitary focal presentation of HT in euthyroid patients has not been described so far. Here we describe a case of localized HT presented with a thyroid mass peripartum, which progressed into diffuse thyroiditis after FNA biopsy. A 27-year-old woman who is 10-day post-partum presents to our endocrine clinic for thyroid mass evaluation noticed by her spouse a few weeks before delivery. The patient has no hypothyroid, hyperthyroid, or mass effect symptoms. On the physical exam: BP 100/64 mmHg, Temp 36.5 C, HR 76 bpm, RR 20 bpm, BMI 24.6 kg/m(2). There is a palpated 5-cm non tender right thyroid nodule. Thyroid stimulating hormone (TSH) is 2.04 uiu/ml (N: 0.3-4.2). Thyroid ultrasound (US) shows a 47×25×31 mm right hyperechoic nodule with some septation of hypoechoic areas. It has thin continuous halo, smooth but lobulated margins and Grade 3 doppler. No microcalcification is seen. Left lobe and isthmus are homogenous with no nodules. There is a reactive lymphadenopathy on the right cervical region. An ultrasound guided-FNA cytology shows clusters of follicular cells forming micro- and macro-follicles with background of hemorrhage but no colloid is seen. Cytology is suspicious of a follicular neoplasm, Bethesda IV category. Diagnostic Lobectomy is discussed but the patient opts for repeat biopsy at a different facility. She presents with a similar cytology result after 3 months. She elects follow up as she remains asymptomatic. After 6 months follow up, she has spontaneous reduction of the nodule size and it is not palpated. Neck US shows diffusely heterogeneous gland with hypoechoic areas and significant reduction in size of the right hyperechoic nodule to 22×14×11 mm. Ultrasound findings are suggestive of thyroiditis and further labs are requested. Thyroid peroxidase antibodies >1000 iu/mL (N: <5.61), anti-thyroglobulin antibodies 161.71 iu/mL (N: <4.11), TSH 3.4 uiu/ml (N: 0.35-4.9), free T4 is 10.38 pmol/L (N: 9-19), thyroglobulin 76.76 ng/mL (N: 3.5-77). These findings suggest that HT may present as a localized form in euthyroid phase and should be considered in the differential diagnosis of thyroid nodule. Serologic evidence of HT and serial US follow-up should be recommended instead of other unnecessary procedures. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.