Myxedema coma (also termed decompensated hypothyroidism) is a rare, life-threatening endocrine emergency resulting from severe, decompensated hypothyroidism, characterized by hypothermia, altered mental status, bradycardia, hypotension, and multiorgan failure, with mortality rates of 25–60% even with treatment. [1-3] The estimated incidence is approximately 2.56 cases per 1 million US persons per year. [2]
1. History
- Known hypothyroidism? Duration, etiology (Hashimoto's, post-thyroidectomy, post-radioactive iodine, post-radiation), current levothyroxine dose, and adherence [2][4]
- Precipitating event? Infection, cold exposure, sedative/opioid use, stroke, MI, GI bleed, surgery, trauma, or medication non-compliance — these are the most common triggers that convert compensated hypothyroidism into crisis [5-7]
- Levothyroxine discontinuation was the most frequent trigger (28%) in one multicenter ICU cohort, followed by sepsis (15%) and amiodarone-related hypothyroidism (11%) [8]
- Symptom timeline: Progressive fatigue, lethargy, cold intolerance, constipation, weight gain, hoarse voice, cognitive slowing preceding the acute decompensation [1][3]
- Important negatives: Deny fever (suggests infection as trigger), deny medication ingestion (overdose mimic), deny head trauma
2. Alarm Features
- Hypothermia (core temp often <35°C, can be <30°C) — present in ~66% of ICU-admitted cases [8]
- Altered mental status ranging from lethargy to frank coma (~52%) [8]
- Hemodynamic failure — hypotension, bradycardia, decreased cardiac output (~57%) [8]
- Hypoventilation / respiratory failure — CO₂ retention, hypoxemia; may require intubation [2][5]
- Seizures (from hyponatremia or hypoglycemia)
- Pericardial effusion with risk of tamponade [4]
- A myxedema score >110 is associated with 100% mortality [9]
3. Medications
Medications that precipitate myxedema coma
- Sedatives, opioids, anesthetics, benzodiazepines
- Amiodarone (can cause hypothyroidism)
- Lithium
- Phenytoin, carbamazepine, rifampin (increase T4 clearance)
- Immune checkpoint inhibitors [2]
Treatment medications (see Treatment Plan below)
- IV levothyroxine (T4): Loading dose 300–500 mcg IV, then 50–100 mcg IV daily [10-12]
- IV liothyronine (T3): May be added in critically ill patients; avoid high doses (associated with mortality) [5][10]
- IV hydrocortisone: 100 mg IV q8h empirically until adrenal insufficiency ruled out — must be given BEFORE or concurrent with thyroid hormone [2][10-11]
Contraindicated: Do not give thyroid hormone without concurrent glucocorticoids — risk of precipitating acute adrenal crisis [11][13]
4. Diet
- NPO initially in most cases (altered mental status, aspiration risk, ileus)
- Correct hypoglycemia with IV dextrose
- Address hyponatremia cautiously (fluid restriction; avoid rapid correction → osmotic demyelination)
- Long-term: No specific dietary restrictions once stabilized; ensure adequate iodine intake
5. Review of Systems
- Neuro: Level of consciousness, confusion, psychosis, seizures, delayed DTRs
- Cardiovascular: Chest pain, dyspnea, edema, exercise intolerance
- Respiratory: Dyspnea, hypoventilation, sleep apnea history
- GI: Constipation, abdominal distension (ileus), decreased appetite
- GU: Oliguria, urinary retention
- Derm: Dry skin, hair loss, diffuse non-pitting edema (myxedema)
- Endocrine: Menstrual irregularities, galactorrhea, symptoms of adrenal insufficiency
6. Collateral History and Family History
- Collateral is critical — patients are often obtunded; obtain history from family, caregivers, pharmacy records
- Confirm thyroid disease history, medication list, recent medication changes or discontinuation
- Family history: Autoimmune thyroid disease (Hashimoto's), other autoimmune conditions (type 1 diabetes, Addison's disease, pernicious anemia) [2][13]
- Social context: Housing status (cold exposure risk), access to medications, substance use
7. Risk Factors
- Older age (especially women >60) [3][14]
- Female sex (80% of cases) [9]
- Known hypothyroidism with medication non-adherence or inadequate dosing [8]
- Undiagnosed hypothyroidism — 54% of ICU-admitted patients had no prior diagnosis [8]
- Prior thyroidectomy or radioactive iodine without adequate replacement [4]
- Winter season — more admissions occur in winter months [14]
- Homelessness (cold exposure, medication non-adherence) [14]
- Comorbid autoimmune conditions (polyautoimmune syndrome)
8. Differential Diagnosis
- Sepsis / septic shock — most important mimic; also the most common precipitant (can coexist)
- Adrenal crisis (Addisonian crisis) — hypotension, hypoglycemia, bradycardia overlap; may coexist [15]
- Hypothermia from environmental exposure — distinguish by thyroid function testing
- Drug overdose / intoxication (opioids, sedatives, beta-blockers) — toxicology screen
- Stroke / intracranial pathology — CT head to rule out
- Pituitary apoplexy — secondary hypothyroidism with headache, visual field deficits [15]
- Non-thyroidal illness syndrome (NTIS / euthyroid sick syndrome) — low T3/T4 but different clinical context; TSH usually not markedly elevated [16]
- Heart failure / cardiogenic shock — pericardial effusion and low output overlap
9. Past Medical History
- Hypothyroidism (Hashimoto's, post-surgical, post-RAI, central)
- Prior episodes of myxedema coma
- Thyroidectomy or neck radiation history [4]
- Other autoimmune diseases (type 1 DM, Addison's, pernicious anemia, vitiligo)
- Cardiac disease (important for dosing decisions — use lower loading doses) [10-11]
- Psychiatric history (lithium use, medication non-compliance)
10. Physical Exam
Vital signs
- Hypothermia (use a low-reading thermometer; standard thermometers may not register)
- Bradycardia (often <60 bpm)
- Hypotension
- Bradypnea / hypoventilation
Focused exam
- General: Obtunded, lethargic, or comatose; diffuse non-pitting edema (myxedema), periorbital puffiness
- HEENT: Macroglossia, hoarse voice, thyroidectomy scar, goiter
- Cardiovascular: Distant heart sounds (pericardial effusion), JVD
- Pulmonary: Decreased breath sounds (pleural effusion), shallow respirations
- Abdomen: Distension, decreased bowel sounds (ileus)
- Neuro: Depressed consciousness, delayed relaxation phase of deep tendon reflexes (classic), hyporeflexia
- Skin: Cool, dry, doughy, yellowish (carotenemia), alopecia
11. Lab Studies
Diagnostic
- TSH — markedly elevated in primary hypothyroidism (may be low/normal in central hypothyroidism) [3][16]
- Free T4 — very low or undetectable [3][16]
- Free T3 / Total T3 — low [16]
Expected metabolic derangements
- Hyponatremia (dilutional, from impaired free water excretion) [2]
- Hypoglycemia [2-3]
- Lactic acidosis [2]
- Elevated CK (rhabdomyolysis from myopathy)
- Hyperlipidemia (elevated cholesterol, LDL)
- Elevated LDH, AST (from muscle/liver involvement)
Rule-out labs
- Random cortisol → rule out concomitant adrenal insufficiency (draw BEFORE giving steroids if possible, but do not delay treatment) [2][10]
- CBC, blood cultures, UA, CXR → evaluate for infectious precipitant
- BMP → electrolytes, glucose, renal function
- ABG/VBG → assess ventilation (CO₂ retention) and acid-base status
- Troponin → cardiac ischemia monitoring
- Coagulation studies → DIC screening in severe cases
12. Imaging
- Chest X-ray: Cardiomegaly (pericardial effusion), pleural effusions, pulmonary edema
- Echocardiography: Pericardial effusion (common), decreased cardiac contractility, assess for tamponade [4]
- CT head: If altered mental status — rule out stroke, pituitary apoplexy, or other intracranial pathology [15]
- Imaging is not required for diagnosis but is essential for identifying precipitants and complications
13. Special Tests
- Myxedema Coma Diagnostic Score: A clinical scoring system incorporating thermoregulatory, CNS, cardiovascular, GI, metabolic, and precipitating event criteria; score >60 is suggestive, >90 predicts higher mortality, >110 associated with 100% mortality [9]
- qSOFA score: High qSOFA independently predicts mortality in myxedema coma (OR 7.1) [9]
- Anti-TPO antibodies: Confirm autoimmune etiology (Hashimoto's)
- ACTH stimulation test: When adrenal insufficiency is suspected (perform after initial empiric hydrocortisone)
- Point-of-care glucose: Immediate bedside check
- Core temperature measurement: Rectal or esophageal probe (standard oral/axillary may be inaccurate)
14. ECG
ECG is essential and may provide the sentinel diagnostic clue: [6]
- Sinus bradycardia (often <60 bpm)
- Low voltage QRS complexes (pericardial effusion)
- QT prolongation (risk of torsades de pointes)
- Osborn (J) waves — positive deflections at the QRS-ST junction, strongly associated with hypothermia; amplitude correlates with degree of temperature depression [6]
- AV conduction delays (first-degree AV block, bundle branch blocks)
- Flattened or inverted T waves
Pearl: Osborn waves can mimic ST-elevation MI — misinterpretation may lead to unnecessary catheterization or thrombolytics. Always check core temperature when Osborn waves are present. [6]
15. Assessment
Myxedema coma is a clinical diagnosis supported by laboratory confirmation. The classic triad is altered mental status + hypothermia + precipitating event in a patient with known or newly discovered severe hypothyroidism. [5][17]
Severity stratification
- Mortality predictors include age >70, need for mechanical ventilation, in-hospital hypotension, high qSOFA score, and myxedema score >90 [8-9]
- SOFA cardiovascular component ≥2 (OR 11.1) and ventilation component ≥2 (OR 4.52) independently predict ICU mortality [8]
Atypical presentations: Not all patients are comatose — many present with altered sensorium short of coma. The term "decompensated hypothyroidism" is increasingly preferred. [17] Central hypothyroidism may present with normal or low TSH, making diagnosis more challenging. [10]
16. Treatment Plan
Initial stabilization (do not delay for lab confirmation): [2][10][17]
- ABCs: Secure airway if GCS depressed; intubate for hypoventilation/respiratory failure
- IV hydrocortisone 100 mg bolus → then 100 mg IV q8h (MUST precede or be given simultaneously with thyroid hormone to prevent adrenal crisis) [2][10-11]
- IV levothyroxine (T4): Loading dose 300–500 mcg IV (use lower end 200–300 mcg for elderly, small patients, or those with cardiac disease), then 50–100 mcg IV daily [10-12]
- IV liothyronine (T3): Consider adding 5–20 mcg IV q8h in critically ill patients; avoid high doses (associated with increased mortality) [5][10]
- Passive rewarming — warm blankets, warm IV fluids; avoid active external rewarming (may cause vasodilation and cardiovascular collapse)
- Correct hyponatremia — fluid restriction; hypertonic saline only if seizures or severe symptomatic hyponatremia
- Correct hypoglycemia — IV dextrose
- Treat precipitating event — empiric broad-spectrum antibiotics if infection suspected (low threshold given blunted febrile response) [5][18]
- Vasopressors if hypotension refractory to fluids (may be poorly responsive until thyroid hormone repleted)
- Transition to oral levothyroxine once clinically improved and tolerating PO (typically within ~1 week) [2]
The following algorithm from the AAFP outlines the treatment approach for primary hypothyroidism, including myxedema coma:
17. Disposition
- All suspected myxedema coma → ICU admission [2][19]
- Mean length of stay is approximately 9.6 days for myxedema coma vs. 4.6 days for other hypothyroidism admissions [14]
- Endocrinology consultation — urgent [3]
- Critical care consultation — for ventilatory and hemodynamic support
- Discharge criteria: Hemodynamically stable, tolerating oral levothyroxine, electrolytes normalized, mental status at baseline, precipitating event treated, reliable follow-up and medication access confirmed
- Never discharge from ED — this is universally an inpatient/ICU diagnosis
18. Follow Up / Return Precautions
- Endocrinology follow-up within 1–2 weeks of discharge
- TSH and free T4 recheck 6–8 weeks after dose stabilization [2]
- Medication adherence counseling — emphasize lifelong need for levothyroxine; discontinuation is the most common preventable trigger [8]
- Adrenal function reassessment if empiric steroids were given
- Return precautions: Return immediately for recurrent lethargy, confusion, cold intolerance, swelling, constipation, or any decline in mental status
- Expected recovery: Clinical and biochemical improvement typically within 1 week with IV therapy; full recovery may take weeks [2]
- Mortality awareness: Even with appropriate treatment, in-hospital mortality ranges from 6.8% to 60% depending on severity and comorbidities [2][8-9]
References
1. Hypothyroidism. — Taylor PN, Medici MM, Hubalewska-Dydejczyk A, Boelaert K. Lancet. 2024.
2. Hypothyroidism. — Chaker L, Papaleontiou M. The Journal of the American Medical Association. 2025.
3. Hypothyroidism: Diagnosis and Treatment. — Wilson SA, Stem LA, Bruehlman RD. American Family Physician. 2021.
4. Comatose Patient With Hypothermia, Dyspnea, and General Edema in the Emergency Department: A Case Report. — Tsai SL, Lin CC, Lin CY, Keng-Wei C, Chien CY. The Journal of International Medical Research. 2018.
5. Thyroid Emergencies: A Narrative Review. — Kruithoff ML, Gigliotti BJ. Endocrine Practice : Official Journal of the American College of Endocrinology and the American Association of Clinical Endocrinologists. 2025.
6. Electrocardiography Unmasking the Cause of Unexplained Coma. — Rajendran G, Mahalingam S, Ramkumar A. JAMA Internal Medicine. 2026.
7. Case Report: Myxedema Coma Caused by Immunoglobulin a Vasculitis in a Patient With Severe Hypothyroidism. — Ito H, Fukuda K, Ashida K, et al. Frontiers in Immunology. 2022.
8. Critically Ill Severe Hypothyroidism: A Retrospective Multicenter Cohort Study. — Bourcier S, Coutrot M, Ferré A, et al. Annals of Intensive Care. 2023.
9. Utility of Myxedema Score as a Predictor of Mortality in Myxedema Coma. — Chaudhary S, Das L, Sharma N, et al. Journal of Endocrinological Investigation. 2023.
10. Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement. — Jonklaas J, Bianco AC, Bauer AJ, et al. Thyroid : Official Journal of the American Thyroid Association. 2014.
11. FDA Drug Label. — Updated date: 2024-07-10. Food and Drug Administration.
12. FDA Drug Label. — Updated date: 2020-12-04. Food and Drug Administration.
13. FDA Drug Label. — Updated date: 2024-10-14. Food and Drug Administration.
14. Clinical Features and Outcomes of Myxedema Coma in Patients Hospitalized for Hypothyroidism: Analysis of the United States National Inpatient Sample. — Chen DH, Hurtado CR, Chang P, Zakher M, Angell TE. Thyroid : Official Journal of the American Thyroid Association. 2024.
15. Diagnosis of Reversible Causes of Coma. — Edlow JA, Rabinstein A, Traub SJ, Wijdicks EF. Lancet. 2014.
16. Thyroid Function in Critically Ill Patients. — Fliers E, Bianco AC, Langouche L, Boelen A. The Lancet. Diabetes & Endocrinology. 2015.
17. Decompensated Hypothyroidism: A Review for the Emergency Clinician. — Bridwell RE, Willis GC, Gottlieb M, Koyfman A, Long B. The American Journal of Emergency Medicine. 2021.
18. Myxedema Coma: Diagnosis and Treatment. — Wall CR. American Family Physician. 2000.
19. What Is Hypothyroidism?. — Roberts K. The Journal of the American Medical Association. 2025.