Hypothyroidism and Myxedema Coma

The clinical manifestations of hypothyroidism reflect one of two changes:
1) Slowed metabolism – accounts for the fatigue, cold intolerance, slow movement and speech, constipation, bradycardia, weight gain, delayed relaxation of DTRs
2) Accumulation of matrix glycosaminoglycans in interstitial spaces – leads to coarse hair and skin, puffy facies, enlarged tongue, hoarseness

The cardiovascular consequences of severe hypothyroidism are mainly bradycardia and decreased contractility, which can precipate or worsen CHF exacerbations. 

Myxedema Coma - hallmarks are Decreased Mental Status and Hypothermia, in addition to exaggerated symptoms of severe hypothyroidism.  Often present as hypotension and bradycardia, hypoventilation, hyponatremia, and hypoglycemia, often with concomitant adrenal insufficiency.

Myxedema Coma is difficult to distinguish from sepsis, and since infection is often the precipitating event in a patient with preexisting hypothyroidism, generally the patients must receive empiric antibiotics until sepsis is ruled out.   As mentioned above, myxedema coma can also present as cardiogenic shock.

Treatment involves Intravenous Thyroid Replacement (IV preferred, since GI absorption is often impaired in these patients) +/- IV hydrocortisone until adrenal insuffiency is ruled out.  Remember that starting IV levothyroxine without treating adrenal insuffiency can precipitate an adrenal crisis.   

(Chanu Rhee MD, 1/21/11)