SAT-620 Two Cases of Atypical Subacute Thyroiditis with Large Solitary Thyroid Nodule

Background: Subacute thyroiditis, an inflammatory condition characterised by localised neck pain is thought to be associated with recent viral illness. Thyroid ultrasound (US) generally shows an enlarged thyroid gland with a homogeneous hypoechoic pattern. Solitary nodules of 2cm have been described. Larger thyroid nodules with suspicious US findings have not been reported. Clinical case: Case one is a 55-year-old woman who presented with a rapidly growing right (R) neck mass associated with compressive symptoms of dysphagia and breathlessness. Thyroid function tests (TFTs) were consistent with subclinical hyperthyroidism. Thyroid US showed a 4cm ill-defined hypervascular lesion in the R thyroid lobe (TL). Fine needle aspiration cytology (FNAC) revealed a follicular lesion with lymphohistiocytic infiltrate. 2 months later, she developed a non-tender firm mass over the left (L) neck. Repeat US revealed a 4cm nodule at the L TL. The R TL appeared small. A Tc-99m pertechnetate thyroid (uptake) scan showed decrease uptake in the L TL. TFTs now showed a TSH of 0.05mIU/L (0.45 - 4.50)*, FT4 of 30pmol/L (8-16)^. ESR was elevated to 65mm/hr (1-20). The FNAC, thyroid uptake scan and biochemistry findings suggest the diagnosis of migratory subacute thyroiditis. Her compressive symptoms improved with Prednisone. She became hypothyroid 2 weeks later, and remained on thyroxine for 6 months. Case two is a 45-year-old woman who was admitted to hospital following a 2 week history of painful L neck swelling, associated with fever, palpitations and 5kg weight loss. These symptoms were preceded by an upper respiratory tract illness 1 week earlier. She was clinically euthyroid with L neck fullness and tenderness. TFTs revealed a TSH of 0.02mIU/L* and a raised FT4 of 27pmol/L^. Thyroid US showed an ill-defined 4.9cm nodule in the L TL. A thyroid uptake scan showed reduced uptake in the L TL, consistent with focal thyroiditis. 3 weeks later, she developed subclinical hypothyroidism, and subsequently achieved spontaneous recovery of her thyroid function. In both cases, subsequent thyroid US showed resolution of the thyroid nodule. Conclusion: 1. Subacute thyroiditis may present atypically as a large solitary nodule with suspicious findings on thyroid US. In the appropriate clinical context, of patients with hyperthyroidism, both thyroid US and uptake scan should be considered. 2. Complete migratory thyroiditis can occur. 3. Despite bilateral TL involvement, hypothyroidism can be transient. 4. When diagnosis of a suspicious thyroid nodule remains unclear, close and watchful monitoring rather than thyroidectomy is the preferred treatment. References:T.Bianda, C.Schmid. De Quervain's subacute thyroiditis presenting as a solitary thyroid nodule. Postgrad Med J. 1998:74(876):602-3. P.C. Bartels, R.O. Boer. Subacute thyroiditis (de Quervain) presenting as painless "cold" nodule. J Nucl Med 1987:28:1488-1490