A 38-year-old woman from Delhi presents with progressive weight loss (8 kg over 3 months), heat intolerance, and tremor. Laboratory investigations reveal elevated free T4 (18 pg/mL, normal 7.5–11) and suppressed TSH (0.01 mIU/L). She denies palpitations or dyspnea at rest. Physical examination shows a non-tender, diffuse thyroid enlargement without nodules. On further questioning, she reports no recent iodine exposure, no neck radiation history, and no family history of autoimmune thyroid disease. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient presents with clinical and biochemical hyperthyroidism (elevated free T4, suppressed TSH) with a diffuse goiter. The differential diagnosis includes Graves' disease, Hashitoxicosis, thyroiditis, and thyroid hormone-secreting adenoma or multinodular goiter. ## Why Thyroid Antibody Testing + Uptake Scan? **Key Point:** Distinguishing the etiology of hyperthyroidism is essential before initiating definitive therapy, as the pathophysiology determines treatment strategy. **High-Yield:** The diagnostic algorithm for hyperthyroidism with goiter: | Finding | Graves' Disease | Thyroiditis | Toxic Nodule | iClinical Pearl:** Thyroid uptake scan (RAIU) directly measures thyroid iodine uptake: - **High uptake** → Graves' disease or toxic nodule (active thyroid hormone synthesis) - **Low uptake** → Thyroiditis or thyroid hormone release from damaged follicles (no active synthesis) **Mnemonic: RAIU Pattern** — **R**adioactive **I**odine **U**ptake: - **High RAIU + diffuse pattern** = Graves' disease → Antithyroid drugs (PTU/MMI) - **Low RAIU + diffuse goiter** = Thyroiditis → Beta-blockers + supportive care - **High RAIU + focal uptake** = Toxic nodule → Radioiodine or surgery ## Stepwise Management Approach 1. **Confirm etiology** via TPO/thyroglobulin antibodies (positive in autoimmune thyroid disease) 2. **If antibodies negative**, perform thyroid uptake scan to differentiate thyroiditis (low uptake) from Graves' disease or toxic nodule (high uptake) 3. **Once etiology confirmed**, initiate appropriate therapy: - Graves' disease → Antithyroid drugs (PTU preferred in 1st trimester if applicable) - Thyroiditis → Supportive care + beta-blockers; antithyroid drugs NOT indicated **Clinical Pearl:** Starting antithyroid drugs blindly in thyroiditis is harmful—these patients do not have overactive thyroid synthesis; they have thyroid inflammation and hormone leakage. Antithyroid drugs will not help and may worsen outcomes. [cite:Harrison 21e Ch 397]