Abstract #1408165: An Atypical Case of Subacute Thyroiditis Presenting as a Toxic Adenoma

Abstract

Subacute thyroiditis is inflammation of the thyroid gland often occurring after a viral infection of the upper respiratory tract. It is an uncommon condition mostly seen in women compared to men and is characterized by neck pain, a tender thyroid on exam with hyperthyroidism on initial presentation and low uptake on radioiodine imaging. A 36-year-old American Indian female with no significant past medical history was referred to Endocrinology for a new diagnosis of hyperthyroidism and for fine needle aspiration of thyroid nodules. Four months prior the patient was experiencing intermittent palpitations along with right sided neck pain. A thyroid ultrasound ordered by her primary care provider showed multiple nodules, including a 1.9 cm heterogeneous nodule with eccentric calcifications in the left lower lobe (TI-RADS 4) and a 2.7 cm right hypoechoic solid nodule with ill-defined borders, taller than wide (TI-RADS 5). Her thyroid function tests revealed a TSH < 0.025 uIU/mL (nl 0.450-4.50 uIU/mL), FT4 2.64 ng/dL (nl 0.82-1.7 ng/dL), FT3 6.4 pg/mL (nl 2.0-4.4 pg/mL) and thyroglobulin antibody < 1.0 IU/ml. A radioactive iodine uptake and scan showed decreased 24-hour uptake with a single hyperfunctioning nodule in the left thyroid lobe. The patient was started on methimazole 10 mg daily which was titrated down to 5 mg daily with normalization of her thyroid function after 3 months of treatment. Repeat thyroid function at the time of her endocrine clinic visit 1 month later revealed hypothyroidism. We performed a bedside ultrasound which did not show any thyroid nodules and the biopsy was cancelled. These findings were supported by a formal thyroid ultrasound a few weeks later. Methimazole was stopped and thyroid function normalized. Further history revealed the patient was experiencing symptoms of an upper respiratory tract infection a few weeks prior to the start of the palpations and neck pain. Six months after initial presentation, thyroid function has remained normal off methimazole. This is a rare case of subacute thyroiditis with initial findings of a toxic adenoma. To our knowledge there is only one other reported case of this unusual presentation of subacute thyroiditis with focal radioiodine uptake and thyroid nodules that later resolved on repeat imaging. This case should raise awareness for other providers to consider subacute thyroiditis when evaluating patients presenting with hyperthyroidism and atypical imaging findings. The history and clinical presentation were key in making the clinical diagnosis.