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

30 C

<27 C

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)

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

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:

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.