How do I recognize and manage thyroid storm and myxedema coma?

Recognition and Management of Thyroid Storm and Myxedema Coma

Thyroid Storm Recognition

Thyroid storm is diagnosed clinically—not by thyroid hormone levels—based on severe hyperthyroidism with systemic decompensation, typically triggered by infection, surgery, or trauma. 1, 2, 3

Cardinal Clinical Features

• Hyperthermia (often >40°C/104°F) out of proportion to any infection 1, 2, 3
• Severe tachycardia (heart rate often >140 bpm) or atrial fibrillation with rapid ventricular response 1, 2, 3
• Central nervous system dysfunction: agitation, confusion, delirium, seizures, or coma 1, 2, 3
• Cardiovascular manifestations: high-output heart failure, hypotension, or shock 2, 3
• Gastrointestinal symptoms: nausea, vomiting, diarrhea, abdominal pain 1, 2

Precipitating Events to Identify

• Infection (most common trigger) 2, 3
• Surgery or trauma 1, 2, 3
• Radioiodine therapy 3
• Medication non-compliance in known Graves' disease 3
• Diabetic ketoacidosis or other acute medical illness 3

Diagnostic Approach

• Do not wait for thyroid function tests to initiate treatment—thyroid hormone levels (elevated FT3, FT4, suppressed TSH) do not distinguish thyroid storm from uncomplicated hyperthyroidism 1, 2, 4
• Diagnosis is purely clinical based on the presence of severe hyperthyroidism plus evidence of systemic decompensation 2, 3, 4
• Scoring systems exist but should not delay treatment if clinical suspicion is high 4

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Thyroid Storm Management

Treatment must begin immediately in an intensive care setting with a multipronged, stepwise approach targeting hormone synthesis, peripheral effects, and supportive care. 1, 3

Step 1: Block Thyroid Hormone Synthesis (First-Line)

• Propylthiouracil (PTU): 500-1000 mg loading dose, then 250 mg every 4 hours (oral, nasogastric, or rectal) 1, 3
  • OR Methimazole: 60-80 mg loading dose, then 20 mg every 4-6 hours 3
  • PTU is preferred because it also blocks peripheral T4-to-T3 conversion 3

Step 2: Block Peripheral Thyroid Hormone Effects

• Beta-blocker (propranolol preferred): 40-80 mg every 4-6 hours orally, or 1-2 mg IV every 10-15 minutes until heart rate <100 bpm 1, 3

  • Propranolol also inhibits peripheral T4-to-T3 conversion 3
  • Use esmolol (50-100 mcg/kg/min IV) if short-acting control needed or contraindications exist 3
  • Caution: Avoid beta-blockers in severe heart failure; consider diltiazem instead 1

• Glucocorticoids: Dexamethasone 2 mg IV every 6 hours or hydrocortisone 100 mg IV every 8 hours 1, 3

  • Blocks peripheral T4-to-T3 conversion and treats possible relative adrenal insufficiency 3

Step 3: Block Thyroid Hormone Release (Give 1 Hour AFTER Thionamide)

• Saturated solution of potassium iodide (SSKI): 5 drops (250 mg) orally every 6 hours 1, 3
  • OR Lugol's solution: 8 drops (500 mg) every 6-8 hours 1
  • OR Sodium iodide: 500-1000 mg IV every 8 hours 1
  • Critical timing: Must give thionamide first to prevent iodine from being used as substrate for new hormone synthesis 3

Step 4: Additional Therapies for Refractory Cases

• Cholestyramine: 4 g orally every 6-8 hours to interrupt enterohepatic circulation of thyroid hormones 1, 3
• Plasmapheresis or therapeutic plasma exchange: For severe cases unresponsive to medical therapy 3
• Emergent thyroidectomy: Consider if medical management fails and patient is stable enough for surgery 1, 3

Step 5: Critical Supportive Care

• Aggressive cooling: Cooling blankets, ice packs (avoid aspirin—increases free thyroid hormone) 1, 3
• Fluid resuscitation: IV crystalloids for dehydration and hypotension 3
• Oxygen and mechanical ventilation if respiratory failure develops 3
• Treat precipitating cause: Antibiotics for infection, manage DKA, etc. 1, 2, 3
• Cardiac monitoring: Continuous telemetry for arrhythmias 3

Common Pitfalls in Thyroid Storm

• Giving iodine before thionamides—this worsens hormone synthesis 3
• Delaying treatment while waiting for thyroid function test results 2, 4
• Using aspirin for fever (displaces thyroid hormone from binding proteins) 3
• Failing to treat underlying precipitant (infection, etc.) 1, 2

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Myxedema Coma Recognition

Myxedema coma is diagnosed clinically in patients with severe hypothyroidism plus altered mental status, hypothermia, and respiratory failure—thyroid hormone levels confirm hypothyroidism but do not distinguish coma from severe hypothyroidism alone. 2, 3, 4

Cardinal Clinical Features

• Hypothermia (core temperature often <35°C/95°F) 2, 3, 4
• Altered mental status: lethargy, confusion, stupor, or coma 2, 3, 4
• Hypoventilation with hypercapnia (CO2 narcosis leading to coma) 2, 3, 4
• Bradycardia and hypotension 3, 4
• Hyponatremia (dilutional from SIADH) 2, 3

Additional Clinical Clues

• History of thyroid disease, radioiodine therapy, or thyroidectomy 4
• Delayed deep tendon reflexes (classic "hung-up" reflexes) 4
• Non-pitting edema (myxedema) 4
• Macroglossia 4
• Precipitating event: infection, cold exposure, sedatives, surgery 2, 3, 4

Diagnostic Approach

• Diagnosis is clinical—do not delay treatment for thyroid function tests 2, 3, 4
• Expect low FT4, elevated TSH (primary hypothyroidism) or low/normal TSH (central hypothyroidism) 3, 4
• Check morning cortisol and ACTH to rule out concurrent adrenal insufficiency 3
• Arterial blood gas typically shows hypercapnia and respiratory acidosis 3, 4

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Myxedema Coma Management

Immediate treatment in an ICU setting includes high-dose thyroid hormone replacement, glucocorticoids (before or with thyroid hormone), and aggressive supportive care for respiratory failure and hypothermia. 3, 4

Step 1: Thyroid Hormone Replacement

• Levothyroxine (T4): 200-400 mcg IV loading dose, then 50-100 mcg IV daily 3, 4
  • PLUS Liothyronine (T3): 5-20 mcg IV loading dose, then 2.5-10 mcg IV every 8 hours for critically ill patients 3
  • T3 is added because peripheral conversion of T4 to T3 is impaired in critical illness 3
  • Use IV route—oral absorption is unreliable in myxedema coma 3

Step 2: Glucocorticoid Coverage (CRITICAL)

• Hydrocortisone: 100 mg IV every 8 hours 3, 4
  • Must give before or simultaneously with thyroid hormone to prevent precipitating adrenal crisis 3
  • Hypothyroidism can mask adrenal insufficiency; thyroid hormone increases cortisol metabolism 3

Step 3: Respiratory Support

• Mechanical ventilation for hypercapnia (PCO2 >50 mmHg) or respiratory acidosis 3, 4
• Hypoventilation is a cardinal feature and often the pathway to coma 4
• Monitor for aspiration pneumonia risk 2

Step 4: Correct Hypothermia

• Passive rewarming with blankets (avoid active external rewarming—can cause vasodilation and cardiovascular collapse) 3, 4
• Core temperature should rise slowly 3

Step 5: Correct Hyponatremia

• Fluid restriction for dilutional hyponatremia (SIADH) 3, 4
• Hypertonic saline (3%) only if severe symptomatic hyponatremia (Na <120 mEq/L with seizures) 3
• Correct slowly to avoid osmotic demyelination syndrome 3

Step 6: Treat Precipitating Cause

• Antibiotics for suspected infection (even if afebrile—hypothermia masks fever) 3, 4
• Discontinue sedatives, narcotics, or other CNS depressants 3, 4
• Manage any concurrent illness (MI, stroke, etc.) 3

Step 7: Hemodynamic Support

• IV fluids cautiously (risk of fluid overload and worsening hyponatremia) 3
• Vasopressors (norepinephrine) if hypotension persists despite fluids 3
• Avoid excessive fluid resuscitation—cardiac output is already reduced 3

Common Pitfalls in Myxedema Coma

• Giving thyroid hormone without glucocorticoid coverage—precipitates adrenal crisis 3
• Using oral thyroid hormone (absorption is unreliable) 3
• Active external rewarming causing cardiovascular collapse 3, 4
• Rapid correction of hyponatremia causing osmotic demyelination 3
• Missing the precipitating infection (patient may be afebrile due to hypothermia) 3, 4
• Delaying mechanical ventilation in the presence of hypercapnia 3, 4

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Key Distinguishing Features

Feature	Thyroid Storm	Myxedema Coma
Temperature	Hyperthermia (>40°C) [2,3]	Hypothermia (<35°C) [2,3]
Heart Rate	Severe tachycardia [2,3]	Bradycardia [3,4]
Mental Status	Agitation, delirium [2,3]	Lethargy, stupor, coma [3,4]
Respiratory	Normal or tachypnea [3]	Hypoventilation, hypercapnia [3,4]
Sodium	Normal or high [3]	Hyponatremia [3,4]
First-Line Rx	Thionamide + beta-blocker [1,3]	IV T4 + T3 + hydrocortisone [3,4]

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Prognosis

• Thyroid storm mortality: 10-30% even with treatment; higher if diagnosis is delayed 3, 4
• Myxedema coma mortality: 25-60% historically; improved with modern ICU care but still high 3, 4
• Both conditions require ICU-level care and early aggressive multimodal therapy to optimize survival 2, 3, 4