Myxedema coma is defined as severe hypothyroidism leading to decreased mental status, hypothermia, and other symptoms related to slowing of function in multiple organs. It is a medical emergency with a high mortality rate. 

Diagnosis

Key clinical features

  1. Altered mental status
    1. Somnolence, lethargy for months
    2. Development of stupor and comatose state
  2. Hypothermia
    1. Also tends to happen in wintertime.
  3. Precipitating event
    1. Cold exposure
    2. Infection
    3. Medications
    4. Trauma
    5. Stroke
    6. Heart failure
    7. GI bleeding
  4. History of possible thyroidal illness
    1. Neck surgery or scars
    2. Radioiodine therapy
    3. Hypothyroidism

Other Diagnostic Clues

  1. Physical examination
    1. Hypothermia
    2. Hypoventilation
    3. Hypotension
    4. Bradycardia
    5. Macroglossia, dry coarse skin, delayed DTRs
  2. Laboratory findings
    1. Anemia
    2. Hyponatremia
    3. Hypoglycemia
    4. Hypercholesterolemia
    5. High CK
    6. Thyroid labs
      1. Very low serum FT4
      2. High serum TSH (usually)

Treatment

Early recognition and therapy of myxedema coma are essential. Treatment should be initiated on the basis of clinical suspicion without waiting for laboratory results.

Steroids and Thyroid Hormone

  1. IV glucocorticoids (stress dose) prior to levothyroxine administration.
    1. e.g. IV hydrocortisone
  2. IV levothyroxine (Strong recommendation).
    1. Loading dose = 200-400 mcg IV
    2. Decrease for older/smaller patients and those with history of coronary artery disease or arrhythmia
    3. Daily maintenance dose (IV or PO route) of 1.6 ug/kg body weight (decrease to 75% if given IV) afterwards
  3. Consider IV liothyronine given that T4 -> T3 conversion might be impaired in myxedema coma. Avoid high doses. Weak recommendation.
    1. 5-20 mcg loading dose
    2. 2.5-10 mcg Q8H maintenance dose
    3. Decrease doses for same indications above
    4. Continue until patient is clearly recovering, and then just do T4 alone.
  4. Therapeutic endpoints
    1. Intravenous levothyroxine treatment in severely hypothyroid patients may lead to improvement in cardiovascular, renal, pulmonary, and metabolic parameters within a week. Serum thyroxine and triiodothyronine concentrations may improve or normalize with a similar time frame, with more gradual improvement in serum TSH.
    2. (1) improved mental status (2) improved cardiac function (3) improved pulmonary function
  5. Laboratory measurements
    1. Follow thyroid hormones Q1-2 days
    2. Optimal levels are not known
    3. Failure of TSH to trend down or thyroid hormone normalization could be considered indications to increase therapy

Treat adjunct derangements

  1. Hyponatremia - fluid restriction
  2. Hypothermia - consider central warming
  3. Hypotension - fluids, pressors
  4. Hypoglycemia - dextrose, steroids
  5. Hypoventilation - consider invasive ventilation

References

  1. EMCrit 292 - IV T3 for Myxedema Coma, A Different Take with Eve Bloomgarden
  2. Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement. Thyroid. 2014;24(12):1670-1751. doi:10.1089/thy.2014.0028
  3. American Thyroid Association Guideline: Treatment of Hospitalized Patients with Hypothyroidism and Use of Thyroid Hormone Analogs (endocrineweb.com)
  4. Myxedema coma - UpToDate