## Clinical Diagnosis This patient presents with classic primary hypothyroidism: elevated TSH with low-normal free T4, supported by clinical features (fatigue, weight gain, constipation, cold intolerance, delayed reflexes, dry skin) and goiter. ## Rationale for Levothyroxine 50 mcg Daily **Key Point:** In newly diagnosed primary hypothyroidism without cardiac disease or severe symptoms, initial levothyroxine dosing is typically 25–50 mcg daily, titrated upward by 25–50 mcg every 6–8 weeks based on TSH response. **High-Yield:** The patient is middle-aged with no mention of cardiac comorbidity; starting at 50 mcg is safe and standard. Levothyroxine has a long half-life (~7 days), so steady state is reached in 4–6 weeks; TSH should be rechecked at 6–8 weeks to assess adequacy. **Clinical Pearl:** Delayed relaxation of ankle reflexes (Achilles reflex delay) is a classic sign of hypothyroidism and confirms the diagnosis. The firm goiter suggests chronic autoimmune thyroiditis (Hashimoto disease), the most common cause in iodine-sufficient regions. ## Why This Approach 1. **Physiologic replacement:** Levothyroxine is the standard of care because it is converted peripherally to T3 as needed, mimicking normal thyroid physiology. 2. **Gradual titration:** Starting low and titrating prevents iatrogenic hyperthyroidism and cardiac stress (especially important if occult coronary disease exists). 3. **Monitoring interval:** 6–8 weeks allows time to reach steady state before reassessment. ## Target TSH The goal is to normalize TSH (typically 0.5–2.5 mIU/L) and relieve symptoms. Most patients require 75–150 mcg daily at steady state.
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