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?
Hyperactive bowel sounds with diarrhea
Facial muscle twitching when the facial nerve is tapped anterior to the ear
A bronze discoloration of the skin over the knuckles
Bounding peripheral pulses and a widened pulse pressure
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?
Obtain an ACTH stimulation test before giving any medication
Restrict fluids and give demeclocycline
Administer metoprolol for sinus tachycardia
Infuse dextrose-containing normal saline and give IV hydrocortisone
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?
Desmopressin (DDAVP)
Furosemide
3% hypertonic saline
Spironolactone
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