Myxedema coma describes a rare, clinical state in which an individual with long-standing preexisting hypothyroidism presents with life-threatening decompensation. 7 In reality, few patients present comatose with severe myxedema. Affected patients are commonly in the geriatric population. Various etiologies may be a precipitant to this syndrome (I§ble 207-4). The clinical presentation is one of a severe decompensated metabolic state that may include an alteration in mental status, hypothermia, bradycardia, hypoventilation, and even cardiovascular collapse ( Table 20Z-5). These findings are not only secondary to a decline in metabolic function but also due to neurovascular and cardiovascular adaptations. Some of these adaptations are similar to those that occur in euthyroid patients exposed to a cold environment (decline in oxygen consumption and heat generation, and redistribution of blood flow centrally). In addition, there is a change in end-organ responsiveness to catecholamines and a decline in cardiac performance. This is due to an absolute diminution in b-adrenergic receptors (decreased inotrope and chronotrope activity). There is also relatively increased a-adrenergic responsiveness resulting in mild diastolic hypertension. 8 Increased CO2 retention occurs because of decreased respiratory muscle strength and diminished ventilatory drive in response to hypercapnia. There is also decreased free-water clearance resulting in a dilutional hyponatremia, impaired gluconeogenesis, and decreased drug clearance that predisposes patients to drug toxicity from medication. 9
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