SAT-336 - A Tender Thyroid with A Twist: Graves Disease Masquerading as Subacute Thyroiditis

Clinical Takeaway:

In acute thyrotoxicosis with overlapping features, radioiodine uptake (RAIU) is essential to distinguish Graves disease from subacute thyroiditis, as clinical response to steroids and ultrasound findings alone may be misleading.

Background:

Accurate differentiation of thyrotoxicosis etiologies is essential, as treatment strategies differ markedly. Subacute thyroiditis and Graves disease may present with overlapping clinical and imaging features, creating diagnostic uncertainty.

Case:

A 53-year-old woman with type 2 diabetes mellitus treated with metformin presented with 5 days of dyspnea, palpitations, restlessness, insomnia, and nausea. She reported 10 lb weight loss and a viral illness including cough and runny nose one month prior. She had no prior thyroid disease or amiodarone exposure. On presentation, she was tachycardic to 162 bpm and hypertensive otherwise afebrile and fully oriented. Examination revealed a mildly enlarged, initially tender thyroid without bruit or ophthalmopathy. EKG showed sinus tachycardia. CTA chest excluded pulmonary embolism. Laboratory evaluation revealed TSH < 0.01 μIU/mL, free T4 3.73 ng/dL, and total T3 338 ng/dL. Burch-Wartofsky score was 40, raising concern for impending thyroid storm. She was treated with intravenous fluids, propranolol, and stress-dose corticosteroids with clinical improvement.

Thyroid ultrasound demonstrated heterogeneous parenchyma with diffusely increased vascularity consistent with thyroiditis. Due to diagnostic uncertainty, antithyroid therapy was deferred initially. Subsequent nuclear medicine scanning with I-123 uptake showed markedly increased diffuse uptake, without hot "spot" suggestive of nodule, confirming diffuse toxic goiter. Corticosteroids were discontinued, and methimazole 10 mg three times daily was initiated with continued beta-blockade.

Discussion:

This case highlights the diagnostic challenge of distinguishing subacute thyroiditis from Graves disease in acute thyrotoxicosis. Viral prodrome, thyroid tenderness, and ultrasound heterogeneity favored thyroiditis, while increased vascularity and high radioiodine uptake supported Graves disease. Clinical improvement with steroids does not exclude Graves disease, and elevated Burch-Wartofsky scores may overestimate storm risk in the absence of fever or CNS dysfunction. Radioiodine uptake remains essential when clinical and imaging findings conflict.

Conclusion:

Diffuse toxic goiter can masquerade as subacute thyroiditis or impending thyroid storm. It can mimic thyroiditis clinically and even on ultrasound. Early radioiodine uptake testing is critical to avoid misdiagnosis and guide definitive therapy. Symptomatic improvement with steroids does not exclude Graves and radioiodine uptake should not be skipped in such ambiguous cases.

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