A 35-year-old woman from a sub-Himalayan region presents with visible diffuse thyroid enlargement (marked **A** in the diagram). On examination, the swelling moves upward with swallowing and downward with tongue protrusion. She reports palpitations, weight loss despite good appetite, heat intolerance, and tremor. Serum TSH is suppressed; free T4 is elevated. Which of the following is the most likely diagnosis?

Explanation

## Why Graves disease with diffuse toxic goiter and autoimmune TSH-receptor stimulating antibodies is right The clinical presentation of a diffuse goiter (**A** in the diagram) that moves with swallowing (pretracheal fascia attachment), combined with hyperthyroid symptoms (palpitations, weight loss despite increased appetite, heat intolerance, tremor), suppressed TSH, and elevated free T4 is pathognomonic for Graves disease. The diffuse symmetric enlargement reflects uniform thyroid tissue stimulation by TSH-receptor antibodies (TRAb/TSI), not nodular or inflammatory pathology. The patient's age (35 years) and female sex align with peak incidence (females > males, age 30–50). Per Harrison 21e Ch 384 and Park 26e, Graves disease is the most common cause of hyperthyroidism and diffuse toxic goiter in iodine-sufficient regions; the autoimmune mechanism (TSH-receptor stimulating antibodies) is the defining pathophysiology. ## Why each distractor is wrong - **Iodine deficiency goiter with diffuse non-toxic colloid enlargement**: While iodine deficiency is endemic in sub-Himalayan regions and causes diffuse non-toxic goiter, it presents with euthyroid or hypothyroid status, NOT hyperthyroidism. TSH would be normal or elevated, not suppressed. This patient's thyroid function is clearly toxic. - **Hashimoto thyroiditis with firm rubbery goiter and anti-TPO antibodies**: Hashimoto causes hypothyroidism (elevated TSH, low free T4), not hyperthyroidism. The goiter is typically firm and rubbery due to lymphocytic infiltration. This patient's suppressed TSH and elevated T4 exclude autoimmune hypothyroidism. - **Subacute granulomatous thyroiditis with painful goiter and elevated ESR**: De Quervain thyroiditis presents with a PAINFUL goiter, high ESR, and transient hyperthyroidism followed by hypothyroidism. The patient does not report pain, and the clinical course is self-limited. The diffuse symmetric goiter and sustained hyperthyroidism favor Graves, not viral thyroiditis. **High-Yield:** Graves disease = diffuse toxic goiter + hyperthyroid symptoms + suppressed TSH + elevated free T4 + TSH-receptor antibodies (TRAb/TSI); moves with swallowing (pretracheal fascia), NOT with tongue protrusion (that is thyroglossal duct cyst). [cite: Harrison 21e Ch 384; Park 26e]