Hypothyroidism

Everything slows down — metabolism, heart rate, reflexes, even thinking. But the most dangerous complication isn't sluggishness; it's myxedema coma, and it can kill quietly.

Hypothyroidism results from insufficient thyroid hormone production, most commonly from Hashimoto's thyroiditis (autoimmune destruction of the gland) or as a consequence of thyroidectomy or radioactive iodine therapy. Without adequate T3 and T4, the body's metabolic rate drops across every system. The patient presents with fatigue, weight gain, cold intolerance, constipation, bradycardia, dry skin, brittle hair, periorbital edema, and a hoarse voice. Reflexes are sluggish (delayed relaxation phase). TSH is the primary screening lab — in primary hypothyroidism, TSH is elevated (the pituitary is screaming for more hormone) while free T4 is low. Levothyroxine (Synthroid) is the standard replacement, taken on an empty stomach 30–60 minutes before breakfast. Myxedema coma is the life-threatening extreme: severe hypothermia, altered consciousness, bradycardia, hypotension, and hypoventilation. It requires emergency IV thyroid hormone, gradual rewarming (avoid rapid external rewarming), and hemodynamic support. Cholesterol and triglycerides are often elevated because lipid metabolism slows. Monitor for cardiac complications, especially in older adults starting replacement therapy — too-rapid correction can precipitate angina or MI.

Key Distinctions

Don't confuse hypothyroidism (high TSH, low T4, everything slow) with hyperthyroidism (low TSH, high T4, everything fast) — the TSH moves opposite to the hormone level. Students mix up myxedema coma (hypothyroid crisis with hypothermia and bradycardia) with thyroid storm (hyperthyroid crisis with hyperthermia and tachycardia). Periorbital puffiness in hypothyroidism is non-pitting myxedema — distinct from the pitting edema of heart failure.

Clinical Pearl

Think "hypo = slow": slow pulse, slow bowels, slow reflexes, slow metabolism. If TSH is high, the thyroid is low — they move like a seesaw.