Hypothyroidism

A 52-year-old woman with Hashimoto's thyroiditis and a 45-year-old man with iodine deficiency both present with hypothyroidism. Which finding best distinguishes these two etiologies?

A 52-year-old woman from rural Maharashtra presents with progressive fatigue, weight gain of 8 kg over 6 months, and constipation. She reports cold intolerance and has noticed thinning of eyebrows. On examination, her pulse is 52/min, blood pressure 138/88 mmHg, skin is dry and pale, and there is a firm, non-tender thyroid enlargement. Laboratory investigations show: TSH 18.5 mIU/L (normal 0.4–4.0), free T4 0.8 ng/dL (normal 0.8–1.8), and anti-TPO antibodies 320 IU/mL (normal <35). What is the most likely diagnosis?

A 52-year-old woman with primary hypothyroidism on levothyroxine replacement presents with persistent fatigue and weight gain despite TSH normalization. Which of the following is NOT a recognized cause of persistent symptoms in adequately treated hypothyroidism?

Regarding the pathophysiology and laboratory findings in primary hypothyroidism, all of the following statements are correct EXCEPT:

A 38-year-old woman with a history of Hashimoto thyroiditis is on levothyroxine replacement. She reports persistent fatigue and weight gain despite reported compliance. Her TSH is 2.5 mIU/L (normal: 0.4–4.0). Which investigation is most appropriate to evaluate the cause of her ongoing symptoms?