A 42-year-old man comes to the clinic reporting progressive fatigue, weakness, and a 6-kg … — USMLE Step 2 CK

A $42$ -year-old man comes to the clinic reporting progressive fatigue, weakness, and a $6$ -kg ( $13.2$ -lb) weight loss over the past $4$ months. He feels constantly cold and reports a significant decrease in libido. His medical history is notable for a traumatic brain injury sustained in a motor vehicle collision $18$ months ago, which required a prolonged intensive care unit stay. Vital signs show a blood pressure of $98/62 \text{ mm Hg}$ while supine and $82/50 \text{ mm Hg}$ while standing. His heart rate is $64\text{/min}$ . On physical examination, the patient appears lethargic. His skin is pale with no areas of hyperpigmentation. The thyroid gland is not palpable. Testicular volume is decreased bilaterally. Laboratory results are as follows:

Sodium: $130 \text{ mEq/L}$
Potassium: $4.1 \text{ mEq/L}$
Thyroid-stimulating hormone (TSH): $1.4 \text{ \mu U/mL}$ (Normal: $0.4-4.0 \text{ \mu U/mL}$ )
Free T4: $0.5 \text{ ng/dL}$ (Normal: $0.9-1.7 \text{ ng/dL}$ )

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

Measurement of early morning serum cortisolCevap
B
Initiation of levothyroxine therapy
C
Magnetic resonance imaging of the pituitary gland
D
Measurement of serum thyrotropin-releasing hormone
E
Initiation of hypertonic saline infusion

Cevap

Measurement of early morning serum cortisol

This patient's presentation of fatigue, cold intolerance, weight loss, orthostatic hypotension, hyponatremia, and decreased libido following a severe traumatic brain injury (TBI) is highly suspicious for panhypopituitarism. The laboratory results show a low free T4 level with an inappropriately normal TSH, which confirms central (secondary) hypothyroidism. The concurrent symptoms of weight loss, orthostatic hypotension, and hyponatremia strongly suggest central adrenal insufficiency. In a patient with suspected central hypothyroidism, it is critical to evaluate the hypothalamic-pituitary-adrenal (HPA) axis prior to initiating thyroid hormone replacement. Thyroid hormone increases the basal metabolic rate and the hepatic clearance of cortisol. If levothyroxine is administered to a patient with undiagnosed and untreated adrenal insufficiency, the accelerated cortisol metabolism can precipitate a life-threatening acute adrenal crisis. Therefore, measuring an early morning serum cortisol level is the most appropriate next step to diagnose adrenal insufficiency so that glucocorticoids can be replaced before or simultaneously with levothyroxine.

Adım Adım Çözüm

Analyze the laboratory data in the context of the patient's symptoms.

The patient has a low free T4 with an inappropriately normal TSH, indicating central (secondary) hypothyroidism.

Primary hypothyroidism would present with an elevated TSH in response to low T4. An inappropriately normal or low TSH points to a hypothalamic-pituitary origin.

Connect the biochemical findings to the clinical history and physical exam.

The history of severe traumatic brain injury (TBI) establishes a risk factor for delayed hypopituitarism. Symptoms of orthostatic hypotension, weight loss, and hyponatremia point to concurrent central adrenal insufficiency.

TBI is a well-recognized cause of hypopituitarism that can manifest months to years after the initial injury. The absence of hyperpigmentation is consistent with central (rather than primary) adrenal insufficiency.

Determine the management priority for suspected panhypopituitarism.

The hypothalamic-pituitary-adrenal (HPA) axis must be evaluated with a morning serum cortisol level (or ACTH stimulation test) before giving thyroid hormone.

Thyroid hormone increases the hepatic clearance of cortisol. Initiating levothyroxine in a patient with untreated adrenal insufficiency can precipitate a fatal acute adrenal crisis.

Anahtar Kavram

In patients with suspected central hypothyroidism, central adrenal insufficiency must be ruled out or treated prior to initiating levothyroxine to avoid precipitating an acute adrenal crisis.

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