A 35-year-old woman from Delhi presents with a 3-month history of progressive fatigue, weight gain of 8 kg, constipation, and cold intolerance. On examination, she has a non-tender diffuse goitre, dry skin, and delayed relaxation of deep tendon reflexes. Her TSH is 18.5 mIU/L (normal 0.4–4.0) and free T4 is 0.8 ng/dL (normal 0.8–1.8). What is the most appropriate next step in management?

Explanation

## Clinical Presentation Analysis The patient presents with classic features of **primary hypothyroidism**: - Symptoms: fatigue, weight gain, constipation, cold intolerance - Signs: diffuse goitre, dry skin, delayed reflexes (Kocher sign) - Laboratory: elevated TSH (18.5) with low-normal free T4 (0.8) ### Why Levothyroxine Is the Next Step **Key Point:** In overt primary hypothyroidism with clear clinical and biochemical evidence, thyroid replacement therapy is initiated immediately without further diagnostic delay. **High-Yield:** The combination of: - Elevated TSH >10 mIU/L - Low-normal or low free T4 - Symptomatic presentation - Presence of goitre ...is diagnostic of primary hypothyroidism and warrants immediate treatment. ### Dosing Strategy | Parameter | Consideration | |-----------|---------------| | Starting dose | 25–50 mcg daily (conservative in older/cardiac patients) | | Titration | Increase by 25 mcg every 6–8 weeks | | Target TSH | 0.5–2.5 mIU/L (pregnancy: 0.1–2.5) | | Monitoring | TSH + free T4 at 6 weeks, then annually | **Clinical Pearl:** Levothyroxine has a long half-life (~7 days), so steady state is reached in 4–6 weeks. Rechecking TSH before 6 weeks is premature and leads to unnecessary dose escalation. ### Why Antibody Testing Is Secondary While anti-TPO and anti-thyroglobulin confirm *autoimmune* aetiology (Hashimoto thyroiditis), they do NOT change immediate management. Treatment is identical regardless of aetiology. Antibody testing is useful for: - Prognostic counselling (risk of other autoimmune disease) - Family screening - Pregnancy planning (increased miscarriage risk) But it is NOT a prerequisite to starting levothyroxine. **Mnemonic:** **TREAT FIRST, CLASSIFY LATER** — In symptomatic hypothyroidism, start replacement before pursuing aetiological workup. ### Why Imaging Is Not Indicated - **Ultrasound/FNA:** Reserved for nodular goitres, suspicious features, or when malignancy is suspected. A diffuse, non-tender goitre in the context of elevated TSH is consistent with autoimmune thyroiditis and does not require imaging. - **Technetium scan:** Rarely used in modern practice; useful only in thyroiditis or thyroid hormone resistance (very rare). [cite:Harrison 21e Ch 405]