8.2 Thyroid, Adrenal & Metabolic Disorders
Key Takeaways
- Hypothyroidism means high TSH with low free T4; hyperthyroidism means low TSH with elevated free T4 — TSH is the most sensitive screening test
- Thyroid storm treatment order matters: beta-blocker first, antithyroid drug (PTU or methimazole), then iodine at least 1 hour later — iodine before the antithyroid drug fuels more hormone synthesis
- After thyroidectomy, the priority is airway: keep a tracheostomy set and IV calcium gluconate at the bedside and assess for stridor, neck swelling, and hypocalcemia (Chvostek and Trousseau signs)
- Addisonian crisis is a hypotensive emergency treated with rapid normal saline, dextrose, and IV hydrocortisone — never withhold steroids while waiting for diagnostic tests
- SIADH causes concentrated urine and dilutional hyponatremia treated with fluid restriction; diabetes insipidus causes massive dilute urine output and hypernatremia treated with desmopressin (central DI)
Hypothyroidism vs Hyperthyroidism
The thyroid-stimulating hormone (TSH) test is the most sensitive screen: in primary disease TSH moves opposite to thyroid hormone. Hypothyroidism shows high TSH, low free T4; hyperthyroidism shows low (suppressed) TSH, high free T4 and T3.
| Feature | Hypothyroidism | Hyperthyroidism |
|---|---|---|
| Metabolism | Slowed | Accelerated |
| Weight | Gain | Loss despite increased appetite |
| Temperature | Cold intolerance | Heat intolerance, sweating |
| Heart rate | Bradycardia | Tachycardia, atrial fibrillation, palpitations |
| GI | Constipation | Frequent stools/diarrhea |
| Mood | Depression, lethargy, slowed mentation | Anxiety, irritability, tremor, insomnia |
| Skin/hair | Dry, coarse; hair loss; nonpitting edema | Warm, moist; fine hair |
| Other | Hoarseness, menorrhagia, elevated cholesterol | Exophthalmos and goiter (Graves), lid lag, brisk reflexes |
Treatment
- Hypothyroidism: Levothyroxine, started low (25-50 mcg) and titrated every 4-6 weeks; elderly and cardiac patients start at 12.5-25 mcg to avoid provoking angina or dysrhythmias. Teach: take on an empty stomach 30-60 minutes before breakfast, separate from calcium, iron, and antacids by 4 hours, and never stop — therapy is lifelong.
- Hyperthyroidism: Antithyroid drugs — methimazole first-line; propylthiouracil (PTU) preferred in the first trimester of pregnancy and in thyroid storm. Both carry a risk of agranulocytosis — teach patients to report fever or sore throat immediately. Radioactive iodine (I-131) ablates the gland (most patients become hypothyroid); propranolol controls tachycardia and tremor while definitive therapy works.
Thyroid Emergencies
Thyroid storm (thyrotoxic crisis)
A life-threatening exaggeration of hyperthyroidism, usually triggered by infection, surgery, trauma, or abrupt antithyroid drug withdrawal. Signs: high fever, severe tachycardia (often above 140), hypertension then heart failure, delirium, agitation, vomiting/diarrhea, progressing to coma. Treatment sequence is a classic exam point:
- Beta-blocker (propranolol) — controls adrenergic symptoms first.
- Antithyroid drug — PTU or methimazole blocks new hormone synthesis.
- Iodine (SSKI or Lugol solution) at least 1 hour AFTER the antithyroid drug — blocks hormone release; giving iodine first provides substrate for more hormone.
- Support: cooling blanket (avoid aspirin, which displaces T4 from binding proteins), IV fluids, oxygen, treat the precipitant; corticosteroids block peripheral T4-to-T3 conversion.
Myxedema coma
The extreme of untreated hypothyroidism: hypothermia, bradycardia, hypotension, hyponatremia, hypoventilation (CO2 retention), hypoglycemia, and decreased level of consciousness. Management:
- ABCs first — these patients often need airway support and mechanical ventilation.
- IV levothyroxine, but give IV hydrocortisone first or concurrently — thyroid hormone accelerates cortisol metabolism and can unmask adrenal insufficiency, triggering crisis.
- Passive rewarming with blankets only — active external warming causes vasodilation and cardiovascular collapse.
- Treat the trigger (infection, cold exposure, sedatives/opioids — which these patients tolerate poorly).
Post-Thyroidectomy Care
The two life threats are airway obstruction and hypocalcemia.
- Airway is priority one. Position semi-Fowler's with the head and neck supported; keep a tracheostomy set, oxygen, and suction at the bedside. Watch for hemorrhage compressing the trachea: neck swelling, tightness of the dressing, a sensation of pressure, and frequent swallowing (blood trickling down the throat). Check the back of the neck and behind the shoulders for dependent blood.
- Recurrent laryngeal nerve damage: assess voice every 2-4 hours; hoarseness and stridor are reportable findings.
- Hypocalcemia from parathyroid damage (normal total calcium 8.5-10.5 mg/dL): numbness and tingling of fingers, toes, and perioral area; positive Chvostek sign (facial muscle twitch when tapping over the facial nerve) and Trousseau sign (carpopedal spasm when a blood pressure cuff is inflated above systolic for 3 minutes). Keep IV calcium gluconate at the bedside; severe tetany can cause laryngospasm and airway obstruction.
Addison's Disease vs Cushing's Syndrome
| Feature | Addison's (hypocortisolism) | Cushing's (hypercortisolism) |
|---|---|---|
| Sodium/potassium | Hyponatremia, hyperkalemia | Hypernatremia, hypokalemia |
| Glucose | Hypoglycemia | Hyperglycemia |
| Blood pressure | Hypotension, orthostasis | Hypertension |
| Skin | Bronze hyperpigmentation | Thin, fragile skin, purple striae, easy bruising |
| Body habitus | Weight loss | Moon face, buffalo hump, truncal obesity, thin extremities |
| Immunity | — | Immunosuppression, masked infection signs |
| Other | Fatigue, salt craving, GI upset | Osteoporosis, poor wound healing, mood changes, hirsutism |
Addisonian (adrenal) crisis
Triggered by stress, infection, or abrupt steroid withdrawal in a patient with adrenal insufficiency. Presents with severe hypotension/refractory shock, hyponatremia, hyperkalemia, hypoglycemia, vomiting, and confusion. Treatment is an emergency and precedes diagnostic confirmation:
- Rapid IV 0.9% sodium chloride with dextrose for volume and hypoglycemia.
- IV hydrocortisone (e.g., 100 mg bolus, then every 6-8 hours) — the definitive treatment.
- Identify and treat the precipitant (cultures, antibiotics for infection).
- Monitor potassium and rhythm closely as treatment shifts electrolytes.
Corticosteroid taper rules
Exogenous steroids suppress the hypothalamic-pituitary-adrenal (HPA) axis. Teach patients on chronic therapy: never stop abruptly (risk of addisonian crisis); taper per schedule so the adrenal glands recover; wear medical identification; and increase the dose during stress (illness, surgery, dental procedures) because the suppressed adrenals cannot mount a cortisol response.
Pheochromocytoma
A catecholamine-secreting adrenal medulla tumor causing episodic severe hypertension with the classic five P's: pressure (hypertension), pain (headache, chest), perspiration (profuse), palpitations (tachycardia), and pallor. Diagnosis is by plasma free or urinary fractionated metanephrines; avoid palpating the abdomen vigorously (can provoke a hypertensive crisis). Preoperative management is a favorite exam point: alpha-adrenergic blockade (phenoxybenzamine or doxazosin) FIRST, then a beta-blocker only after alpha blockade is established — beta-blockade alone leaves unopposed alpha vasoconstriction and can worsen hypertension.
SIADH vs Diabetes Insipidus
Both disorders involve antidiuretic hormone (ADH) and derange sodium balance in opposite directions.
| Feature | SIADH (too much ADH) | Diabetes Insipidus (too little ADH effect) |
|---|---|---|
| Water balance | Retained (dilutional) | Lost in massive urine output |
| Serum sodium | Hyponatremia (below 135) | Hypernatremia (above 145) |
| Urine | Concentrated, high osmolality, low volume | Dilute, specific gravity 1.001-1.005, output 4-15+ L/day |
| Serum osmolality | Low | High |
| Common causes | Small-cell lung cancer, CNS disorders, SSRIs, anticonvulsants | Head injury, pituitary surgery (central); lithium, hypercalcemia (nephrogenic) |
| Key risks | Cerebral edema, seizures (sodium below 120) | Hypovolemic shock, dehydration |
| Treatment | Fluid restriction (often 800-1,000 mL/day); 3% hypertonic saline with careful monitoring for severe symptomatic hyponatremia; demeclocycline for chronic SIADH | Replace free water (oral or IV hypotonic fluids); desmopressin (DDAVP) for central DI; thiazides or treat cause for nephrogenic DI |
Safety pearls: correct chronic hyponatremia no faster than about 8-12 mEq/L in 24 hours to avoid osmotic demyelination syndrome (locked-in syndrome). For a post-craniotomy or post-pituitary-surgery patient with sudden copious pale urine, suspect DI and report immediately — fluid balance can collapse within hours. Weigh daily and track strict intake and output in both conditions; a 1 kg weight change approximates 1 liter of fluid.
A client 12 hours after a total thyroidectomy reports tingling around the mouth and in the fingertips. Which finding would further support the nurse's suspicion of hypocalcemia?
A patient with Addison's disease develops vomiting, a temperature of 39.1 C, blood pressure 78/48 mm Hg, and glucose 52 mg/dL. Which orders should the nurse implement first?
A patient recovering from pituitary surgery suddenly voids 900 mL of pale urine in 2 hours. Urine specific gravity is 1.002 and serum sodium is 150 mEq/L. Which medication does the nurse anticipate?