## Diagnosis and Management of Hypothyroidism ### Correct Features of Hypothyroidism **Key Point:** Primary hypothyroidism is characterized by elevated TSH with low or low-normal free T4. This reflects the pituitary's appropriate compensatory response to thyroid failure. **Clinical Pearl:** Levothyroxine absorption is impaired by food, calcium, iron, and proton pump inhibitors. Taking it on an empty stomach 30–60 minutes before breakfast significantly improves bioavailability and is standard practice. **High-Yield:** Cold intolerance, weight gain, fatigue, bradycardia, dry skin, and delayed reflexes are hallmark signs of hypothyroidism due to decreased metabolic rate. ### Myxedema Coma Management — The Critical Exception **Warning:** Myxedema coma is a life-threatening emergency, but the first-line agent is **intravenous levothyroxine (T4), NOT liothyronine (T3)**. | Aspect | Detail | | --- | --- | | **First-line agent** | IV levothyroxine (loading dose 200–500 μg, then 50–100 μg daily) | | **Why T4 first** | T4 is peripherally converted to T3 as needed; provides more stable, physiologic replacement | | **Role of T3** | Reserved for severely symptomatic patients or when T4 conversion is impaired; used as adjunct, not monotherapy | | **Supportive care** | Passive rewarming, glucose, fluid/electrolyte correction, mechanical ventilation if needed | | **Mortality** | 20–50% even with treatment; requires ICU monitoring | **Mnemonic:** **MYXEDEMA** = **M**yxedema coma needs **T4** (levothyroxine), not T3 — remember the "4" in "T4" and "40%" mortality rate. ### Summary Table: Hypothyroidism Features | Feature | Status | Notes | | --- | --- | --- | | TSH + low T4 (primary) | ✓ Correct | Diagnostic hallmark | | Levothyroxine timing | ✓ Correct | 30–60 min before food | | Myxedema coma: IV T3 first | ✗ **INCORRECT** | IV T4 is first-line | | Cold intolerance, weight gain | ✓ Correct | Classic symptoms | [cite:Harrison 21e Ch 376]
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