AM Report 1/11/17: Myxedema Coma

Osborn Waves (J Waves):

  • The Osborn wave (J wave) is a positive deflection at the J point
  • It is usually most prominent in the precordial leads
  • Typically associated with hypothermia (typically < 30 C), but they are not pathognomonic; Also seen in: hypercalcemia, neurological insults, medication side effect
  • Height of the Osborn wave is roughly proportional to the degree of hypothermia

 

32.5 C

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30 C

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<27 C

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Thyroid Regulation:

  • TRH (a tripeptide amide) formed in the hypothalamus and travels to the anterior pituitary where it stimulates the release of TSH.

TSH has 3 main effects:

  • ↑ release of preformed thyroid hormone
  • ↑ formation of thyroid hormone
  • ↑ size/number of thyroid cells

Synthesis of T3 and T4 (very complicated) requires two main components thyroglobulin and iodine.

4 physiologic effects of T3 and T4:

  • ↑ basal metabolic rate (↑ heat generation, ↑ O2 consumption)
  • ↑ metabolism (↑ gluconeogenesis, ↑ glycolysis, ↑ glucose absorption, ↑ lipolysis, ↑ protein turnover)
  • Stimulates bone maturation and growth
  • ↑ cardiac output (↑ HR, ↑ contractility)

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Wolff Chaikoff effect: reduced thyroid hormone following large ingestion of iodine; explains potential hypothyroidism cased by amiodarone.

Jod-Basedow effect: iodine-induced hyperthyroidism in a patient with an endemic goiter

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Myxedema Coma:

3 key features:

  • Altered mental status: despite the name, most patients do not present in coma, but usually with confusion/lethargy
  • Hypothermia: due to decrease in thermogenesis that accompanies the decrease in metabolism
  • Precipitating event: look for cold exposure, infection, drugs (diuretics, sedatives, analgesics), trauma, stroke, heart failure, GI bleed, etc.

Pathogenesis:

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Typical presenting patient: older female presenting in the wintertime (often with a history of hypothyroidism)

  • Female > Male 4:1
  • Almost exclusively > 60 years old
  • 90% of cases during the winter months

If diagnosis is suspect, labs to get include:

  • TSH
  • FT4
  • Cortisol

Pearl: without a frankly low T4 level, myxedema coma is unlikely, regardless of the TSH elevation

Myxedema coma is an endocrine emergency and should be treated aggressively – mortality rate 20-40%

Treatment:

  • Thyroid replacement – controversial about type of replacement: Levothyroxine (T4) versus Liothyronine (T3), but initially route of administration should be IV given potential for impaired GI absorption
  • Stress dose steroids – patients with secondary hypothyroidism may have associated hypopituitarism and secondary adrenal insufficiency
  • Supportive measures – ICU management, mechanical ventilation (if necessary), IVF, vasopressors, rewarming, etc.

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