A 25-year-old woman is evaluated for anterior neck pain, fatigue, exercise intolerance, excessive sweating, and tremors that began 6 weeks ago. Other than an upper respiratory infection 2 months ago, she has been healthy. Medical history is otherwise unremarkable, and she takes no medications.
On physical examination, pulse rate is 105/min. Other vital signs are normal. The patient's thyroid gland is tender to palpation and is without discrete nodules. No thyroid bruit is auscultated. Bilateral lid lag is noted, but there is no proptosis, conjunctival injection, or chemosis. There is a fine tremor of her outstretched hands. Deep tendon reflexes are brisk.
Laboratory studies show a serum thyroid-stimulating hormone (TSH) level less than 0.01 µU/mL (0.01 mU/L), a serum free thyroxine (T4) level of 2.8 ng/dL (36.1 pmol/L), and a serum total triiodothyronine (T3) level of 190 ng/dL (2.9 nmol/L). Urine pregnancy test is negative.
Which of the following is the most likely diagnosis?
A. Graves disease
B. Molar pregnancy
C. Subacute thyroiditis
D. Toxic multinodular goiter
MKSAP Answer and Critique
The correct answer is C. Subacute thyroiditis. This content is available to MKSAP 18 subscribers as Question 7 in the Endocrinology and Metabolism section. More information about MKSAP is available online.
The most likely diagnosis is subacute thyroiditis. Subacute thyroiditis is an uncommon cause of thyrotoxicosis that presents following a viral upper respiratory tract infection and is distinguished by a tender or painful thyroid. This is a form of destructive thyroiditis resulting from the leakage of stored thyroid hormone from damaged thyroid follicles. The diagnosis can be confirmed by determining radioactive iodine uptake, which would be low (<10%). Management is aimed at controlling symptoms. This includes treatment with β-blockers and pain control with NSAIDs or, less commonly, glucocorticoids. In most cases, thyrotoxicosis typically lasts 2 to 6 weeks. It is followed by a hypothyroid phase after stored thyroid hormone is depleted, typically lasting 6 to 12 weeks. The patient may become clinically hypothyroid and require temporary levothyroxine therapy. Most patients with thyroiditis eventually recover to a euthyroid state.
Graves disease is the most common cause of thyrotoxicosis in the United States and most frequently affects young women. This patient does not have pathognomic features of Graves disease (thyroid bruit, eye disease, or dermopathy), making this an unlikely diagnosis.
Molar pregnancy is a rare cause of hyperthyroidism resulting from the binding of human chorionic gonadotropin (HCG) to the thyroid-stimulating hormone (TSH) receptor in the setting of very high HCG levels. The negative pregnancy test excludes this diagnosis.
Nodular thyroid disease (toxic adenoma and multinodular goiter) is the next most common cause of thyrotoxicosis after Graves disease and is more commonly seen in older adults. This patient lacks palpable thyroid nodules on examination, which is usually seen with hyperthyroidism from nodular thyroid disease. In addition, neither Graves disease nor nodular thyroid disease cause thyroid pain.
- Subacute thyroiditis is an uncommon cause of thyrotoxicosis that presents following a viral upper respiratory tract infection and is distinguished by a tender or painful thyroid, suppressed thyroid-stimulating hormone, and elevated serum free thyroxine.