Paramedics bring a lethargic 68-year-old male to the emergency department after his family… — USMLE Step 2 CK

Paramedics bring a lethargic $68$ -year-old male to the emergency department after his family found him confused and severely weak at home. The patient has a medical history of hypertension, hyperlipidemia, and type 2 diabetes mellitus. Vital signs upon arrival reveal a temperature of $34.8^\circ$ C ( $94.6^\circ$ F), blood pressure of $80/50$ mmHg, heart rate of $46$ /min, and respiratory rate of $8$ /min. On physical examination, the patient is somnolent but arousable to painful stimuli. His skin is cool, dry, and pale. There is non-pitting edema of the bilateral lower extremities, and deep tendon reflexes exhibit delayed relaxation phases. Lungs are clear to auscultation bilaterally, and cardiac examination reveals profound bradycardia with a regular rhythm. Initial laboratory studies show the following:

Serum sodium: $128$ mEq/L
Serum potassium: $4.0$ mEq/L
Serum chloride: $94$ mEq/L
Serum bicarbonate: $26$ mEq/L
Blood urea nitrogen: $18$ mg/dL
Serum creatinine: $1.1$ mg/dL
Serum glucose: $58$ mg/dL

Thyroid-stimulating hormone (TSH): $1.1$ $\mu$ U/mL (normal: $0.4-4.0$ $\mu$ U/mL)
Free thyroxine (T4): $0.3$ ng/dL (normal: $0.9-1.7$ ng/dL)

Arterial blood gas on room air:
pH: $7.22$
PaCO2: $65$ mm Hg
PaO2: $60$ mm Hg

Which of the following is the most appropriate initial step in the management of this patient?

Administer intravenous hydrocortisone followed by intravenous levothyroxineCevap
B
Administer intravenous levothyroxine and initiate passive rewarming
C
Initiate noninvasive positive pressure ventilation and administer nebulized ipratropium-albuterol
D
Obtain blood cultures and administer empirical intravenous vancomycin and cefepime
E
Administer a continuous infusion of sodium bicarbonate

Cevap

The most appropriate initial step is to administer intravenous hydrocortisone followed by intravenous levothyroxine.

The patient presents with classic signs of myxedema coma (hypothermia, bradycardia, altered mental status, and delayed reflexes). The laboratory finding of a very low free T4 combined with an inappropriately normal TSH points to central (secondary) hypothyroidism. In such cases, there is a high likelihood of concurrent panhypopituitarism, including central adrenal insufficiency (further supported by the patient's hypoglycemia). The standard of care mandates that intravenous glucocorticoids (e.g., hydrocortisone) be given prior to or simultaneously with intravenous levothyroxine. Administering thyroid hormone alone acutely increases the basal metabolic rate and accelerates the hepatic clearance of cortisol, which can precipitate a fatal Addisonian crisis in a cortisol-deficient patient.

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Analyze the clinical presentation and vital signs.

The patient exhibits severe hypothermia, bradycardia, hypoventilation, hypotension, and delayed deep tendon reflexes.

These findings are hallmark signs of a profound hypometabolic state, specifically myxedema coma.

Interpret the endocrine laboratory results.

The free T4 is markedly low (

0.3

ng/dL) while the TSH is inappropriately normal (

1.1

\mu

U/mL).

This discrepancy indicates secondary (central) hypothyroidism rather than primary hypothyroidism. The accompanying hypoglycemia further suggests panhypopituitarism with central adrenal insufficiency.

Determine the correct pharmacological sequence for management.

Intravenous glucocorticoids (hydrocortisone) must be administered prior to intravenous thyroid hormone replacement.

Levothyroxine rapidly increases the basal metabolic rate and hepatic clearance of cortisol. In a patient with unrecognized adrenal insufficiency, this will precipitate a fatal acute adrenal crisis.

Anahtar Kavram

In myxedema coma, especially with laboratory evidence pointing toward central hypothyroidism (low free T4, inappropriately normal TSH), empiric intravenous glucocorticoids must be administered before levothyroxine to prevent precipitating an acute adrenal crisis.

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