A 35-year-old woman presents with a 3-month history of fatigue, weight gain of 8 kg, cold intolerance, and dry skin. On examination, she has a non-tender diffuse goitre and delayed relaxation of deep tendon reflexes. TSH is 18 mIU/L (normal 0.4–4 mIU/L) and free T₄ is 8 pmol/L (normal 10–20 pmol/L). Anti-TPO antibodies are positive. What is the most appropriate next step in management?

Explanation

## Clinical Diagnosis This patient has **primary hypothyroidism secondary to autoimmune thyroiditis (Hashimoto's thyroiditis)**, confirmed by: - Elevated TSH with low free T₄ (primary pattern) - Anti-TPO antibodies positive - Classic symptoms: fatigue, weight gain, cold intolerance, dry skin - Goitre with delayed reflexes ## Management Algorithm ```mermaid flowchart TD A[Confirmed primary hypothyroidism]:::outcome --> B{Symptoms present?}:::decision B -->|Yes| C[Start levothyroxine replacement]:::action C --> D[Initial dose: 25-50 μg daily]:::action D --> E[Recheck TSH in 6-8 weeks]:::action E --> F[Titrate by 25-50 μg increments]:::action F --> G[Target TSH: 0.5-2.5 mIU/L]:::outcome B -->|No| H[Observation, recheck TSH in 6-12 months]:::action ``` ## Rationale for Correct Answer **Key Point:** In symptomatic primary hypothyroidism with confirmed diagnosis (elevated TSH + low free T₄ + positive autoimmune markers), **levothyroxine replacement is the definitive treatment** — not investigation. **High-Yield:** The standard starting dose in non-pregnant, non-cardiac adults is **25–50 μg daily**. A lower starting dose (25 μg) is preferred in this patient because: - She is symptomatic (risk of over-replacement complications) - No cardiac history mentioned (but safer to start low) - Allows gradual titration to avoid iatrogenic thyrotoxicosis **Clinical Pearl:** TSH should be rechecked **6–8 weeks after initiation** (time to reach steady state on a fixed dose). Dose is then adjusted by 25–50 μg increments until TSH normalizes (target 0.5–2.5 mIU/L for most patients). ## Why NOT Ultrasound or Biopsy? **Warning:** Thyroid ultrasound and biopsy are **not routine** in autoimmune hypothyroidism: - Diagnosis is already confirmed (TSH, free T₄, anti-TPO) - Ultrasound is indicated only if nodules are palpable or there is clinical suspicion of malignancy (absent here) - Biopsy is never first-line for Hashimoto's — diagnosis is serological ## Why NOT Propranolol? **Tip:** Propranolol and TSH suppression are used in **hyperthyroidism** (Graves' disease, thyroiditis), not hypothyroidism. This is a common distractor in exams.