10.2 Adrenal Crisis, Thyroid Storm & Myxedema Coma

10.2 Adrenal Crisis, Thyroid Storm & Myxedema Coma

Clinical Scenario: A 62-year-old female on chronic prednisone 15 mg daily presents in shock after abruptly stopping steroids 7 days ago during gastroenteritis. Vital signs: BP 72/40 mmHg refractory to 3 L saline, HR 124 bpm, RR 24, temp 38.9°C. Exam reveals lethargy and diffuse abdominal guarding without peritonitis. Norepinephrine (0.3 mcg/kg/min) and vasopressin (0.04 units/min) fail to maintain MAP > 55 mmHg. Labs: sodium 126 mEq/L, potassium 4.1 mEq/L, bicarbonate 16 mEq/L, glucose 52 mg/dL, and lactate 4.6 mmol/L.

Acute Adrenal Crisis: Etiology & Pathophysiology

Acute adrenal crisis represents life-threatening adrenocortical insufficiency characterized by vasoplegic distributive shock. Cortisol plays an obligatory permissive role in vascular tone by upregulating alpha-1 adrenergic receptors on vascular smooth muscle and inhibiting endothelial nitric oxide synthase. In cortisol deficiency, vascular responsiveness to catecholamines collapses:

• Primary Adrenal Insufficiency (Addison Disease): Destruction of the entire adrenal cortex (autoimmune adrenalitis, adrenal hemorrhage in Waterhouse-Friderichsen syndrome or HIT, tuberculosis). Involves all three cortical zones, causing deficiencies in cortisol, aldosterone, and androgens. Aldosterone deficiency impairs distal tubular sodium reabsorption and potassium excretion, producing hyperkalemia, hyponatremia, and hypovolemia. Loss of cortisol negative feedback drives excessive pituitary POMC synthesis, which cleaves into ACTH and melanocyte-stimulating hormone (MSH), causing pathognomonic cutaneous hyperpigmentation (palmar creases, buccal mucosa).
• Secondary & Tertiary Adrenal Insufficiency: Pituitary ACTH deficiency or hypothalamic suppression, most commonly from abrupt cessation of chronic exogenous corticosteroids (>5 mg prednisone daily for >3 weeks).
  • Aldosterone Sparing: The renin-angiotensin-aldosterone system independently regulates the zona glomerulosa; ACTH is not the primary regulator. Therefore, aldosterone secretion is preserved. Serum potassium remains normal, skin hyperpigmentation is absent, and volume loss is less severe.

Diagnostic Evaluation & Cosyntropin Stimulation

• Clinical Features: Vasopressor-refractory shock, fever, abdominal pain mimicking an acute surgical abdomen, vomiting, hypoglycemia, and altered mentation.
• Cortisol Interpretation: Critical illness and altered cortisol-binding proteins complicate total-cortisol interpretation. A very low value heightens suspicion but a single random cortisol does not establish the diagnosis. Obtain cortisol and ACTH before steroids if this causes no treatment delay.
• High-Dose Cosyntropin Stimulation Test: Administer synthetic ACTH (cosyntropin 250 mcg IV/IM); measure cortisol at 0, 30, and 60 minutes. Interpret the peak using the laboratory’s assay-specific cutoff; the historical threshold is about 18 mcg/dL. Confirmatory testing must not delay crisis treatment.
• Emergency Management Rule: NEVER DELAY CORTICOSTEROID ADMINISTRATION FOR DIAGNOSTIC TESTING.
• Treatment Before Confirmation: Give hydrocortisone immediately and defer stimulation testing until recovery if necessary. Hydrocortisone is cortisol and affects subsequent measurements; coordinate later testing with endocrinology. Dexamethasone generally does not cross-react with cortisol assays, but preserving a delayed test does not make it the preferred crisis treatment.

Emergency Pharmacotherapy for Adrenal Crisis

1. Glucocorticoid Replacement: Hydrocortisone 100 mg IV stat, followed by 200 mg/24 h continuous infusion or 50 mg IV every 6 hours. Doses $\ge 100$ mg/day provide saturating mineralocorticoid activity, making oral fludrocortisone unnecessary during the acute phase.
2. Volume & Glucose Resuscitation: Infuse 0.9% Normal Saline with 5% Dextrose (D5 0.9% NS) at 1,000 mL in hour 1, then 250–500 mL/hr to restore intravascular volume and correct hypoglycemia.
3. Recovery Phase: As shock resolves, taper hydrocortisone to oral maintenance. Initiate oral fludrocortisone (0.05–0.2 mg daily) for primary insufficiency once hydrocortisone is below 50 mg/day.

Thyroid Storm: Pathophysiology & Management Protocol

Thyroid storm is a life-threatening hypermetabolic crisis triggered by infection, surgery, trauma, or non-compliance in thyrotoxic patients:

• Diagnostic Scoring: Assessed via the Burch-Wartofsky Point Scale (BWPS): score $\ge 45$ indicates thyroid storm, 25–44 impending storm, and $< 25$ unlikely. Evaluates thermoregulatory failure (temp $> 38–40^\circ\text{C}$), CNS effects (agitation to coma), GI-hepatic dysfunction (jaundice, diarrhea), and cardiovascular collapse (tachycardia $> 140$ bpm, atrial fibrillation, acute pulmonary edema).
• Coordinated Multimodal Treatment: Begin supportive care and treat the precipitant concurrently. Give corticosteroids promptly; only iodide requires the specific delay below.
  1. Block Beta-Adrenergic Tone: Assess perfusion and ventricular function first. In a stable patient, propranolol 60–80 mg PO/NG every 4–6 hours controls adrenergic symptoms and reduces peripheral conversion. Use cautious, monitored dosing; short-acting esmolol permits rapid adjustment. Beta-blockade can precipitate collapse in decompensated systolic failure or cardiogenic shock.
  2. Inhibit New Hormone Synthesis: Propylthiouracil (PTU) 500–1,000 mg loading PO/NG/PR, then 200–250 mg every 4 hours. PTU is preferred over methimazole in storm because it simultaneously inhibits thyroid peroxidase and blocks peripheral T4-to-T3 deiodination.
  3. Inhibit Hormone Secretion (Wolff-Chaikoff Effect): Saturated Solution of Potassium Iodide (SSKI) 5 drops PO/NG every 6 hours or Lugol solution 10 drops PO/NG every 8 hours.
  4. Inhibit Peripheral Conversion & Support Adrenal Reserve: Hydrocortisone 100 mg IV every 8 hours to block T4-to-T3 conversion and treat relative adrenal exhaustion from accelerated cortisol turnover.

Myxedema Coma: Decompensated Hypothyroidism

Myxedema coma is the extreme decompensation of hypothyroidism, provoked by infection, cold, sedatives, or trauma:

• Clinical Pentad:
  1. Hypothermia: Core temp often $< 35.5^\circ\text{C}$ ($< 32^\circ\text{C}$ in severe cases).
  2. Hypoventilation: Hypercapnic respiratory failure from blunted ventilatory drive and muscle weakness; early mechanical ventilation is often required.
  3. Cardiovascular Decompensation: Sinus bradycardia, low cardiac output, pericardial effusion, hypotension.
  4. Neuropsychiatric Depression: Lethargy, stupor, or coma with delayed reflex relaxation.
  5. Metabolic Derangements: Hyponatremia (impaired water excretion) and severe hypoglycemia.
• Critical Care Management:
  • Adrenal Coverage Precedes Thyroid Hormone: Administer Hydrocortisone 100 mg IV every 8 hours BEFORE thyroid hormone. Thyroid hormone accelerates hepatic cortisol clearance; giving levothyroxine without steroids in unrecognized hypopituitarism precipitates fatal adrenal collapse.
  • Thyroid Hormone Replacement: IV Levothyroxine (T4) 200–400 mcg loading dose, then 50–100 mcg IV daily. In severe obtundation, add IV Liothyronine (T3) 5–20 mcg loading dose, then 2.5–10 mcg every 8 hours (use caution in CAD due to arrhythmia risks).
  • Passive Rewarming: Use passive external rewarming (blankets). Active external rewarming (forced-air warming blankets) is strictly contraindicated; rapid cutaneous vasodilation shunts core blood, causing fatal cardiovascular collapse.