A 49-year-old woman presents with progressive enlargement of the base of her neck. Close questioning reveals a history of palpitations, easy fatigability, insomnia, tremors, and excessive sweating for two months, along with a five-kilogram weight loss during the same period. Her husband also mentions that she prefers to keep the temperature at home on the lower side. She has refused to seek medical advice thus far. However, being a professional singer, she is now worried about the possible repercussions on her voice. She was diagnosed with type 2 diabetes mellitus three years ago, which is well controlled on metformin alone. Her surgical and gynecological histories are unremarkable, with her menopause occurring two years ago. Her random blood sugar and HbA1c are respectively 134 mg/dL (target: <180 mg/dL) and 6.0% (target: <7.0%). Serum electrolytes and a renal profile are both within normal parameters. A 12-lead ECG reveals a sinus tachycardia of 100 bpm, with no other rate, rhythm, or morphological abnormalities.
TSH: 0.17 mIU/L (0.4 - 4.5) Total T3: 220 ng/dL (80 - 180) Free T4: 3.2 ng/dL (0.8 - 1.8)
The ultrasound reveals a diffusely enlarged hypoechogenic thyroid gland with increased vascularity. No nodules are noted.
Serum TSH receptor antibody (TRAb) levels: 8.7 IU/L (<1.75 IU/L)
The technetium-99 (Tc-99m) scan demonstrates uniform uptake throughout the thyroid gland. The five-hour iodine uptake is high, at 53%.