A 45 years old woman presented with origin of a thyroid nodule. One year earlier, she had discovered a painless lump in her neck, which was found to be well-circumscribed in the left thyroid lobe by ultrasonography. A 123I scan concentrated 20% of the radioisotope mainly in the palpable nodule. The surrounding thyroid tissue showed little uptake of radionuclide. Her serum free thyroxine index (FTI) was 8.0 µg/dl (normal 4.0 to 11.5), which agreed with the clinical impression of euthyroidism. Over the previous year without therapy, the nodule enlarged from 3 to 5 cm by physical examination and ultrasonography. The patient recently developed nervousness and tremor.
Physical Examination:
Temperature 98.4o, pulse 98, respiration rate 16, blood pressure 120/60 mm Hg. General appearance: euthyroid. Skin: normal. Neck: large, easily visible, 5 cm, well- circumscribed left anterior neck mass not adherent to adjacent structures; moved upward when she swallowed; left thyroid lobe not palpable; no cervical lymph nodes palpable. Cardiac: normal. Abdomen: normal. Musculoskeletal: normal, good proximal muscle strength.
Laboratory Findings:
WBC 4,600/ µl with normal differential Hct 45%. FTI 11.5 µ(normal 4.0-11.5), TSH <0.1 µU/ml I ( normal 0.5- 5.0), thyroidal 123I uptake 40% at 24 hours. Thyroid scan: shown below.
Question: What is the probable cause and functional status of the thyroid nodule?
