A 58-year-old man comes to the clinic due to 4 months of progressive fatigue, decreased li… — USMLE Step 2 CK

A 58-year-old man comes to the clinic due to 4 months of progressive fatigue, decreased libido, and lightheadedness upon standing. He also reports a $4$ -kg ( $8.8$ -lb) weight loss despite a normal appetite, and frequent episodes of nausea. Physical examination reveals a blood pressure of $102/64$ mm Hg supine and $86/55$ mm Hg standing. His pulse is $62$ /min. The patient's skin appears pale without hyperpigmentation. Neurologic examination shows a delayed relaxation phase of the deep tendon reflexes. Laboratory studies are obtained and shown below:

Laboratory Test	Result	Reference Range
Serum sodium	$131$ mEq/L	$136-145$ mEq/L
Serum potassium	$4.1$ mEq/L	$3.5-5.0$ mEq/L
Thyroid-stimulating hormone (TSH)	$2.1$ $\mu$ U/mL	$0.4-4.0$ $\mu$ U/mL
Free thyroxine (T4)	$0.4$ ng/dL	$0.9-1.7$ ng/dL

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

A
Initiation of levothyroxine therapy
Measurement of serum early morning cortisolCevap
C
Measurement of serum thyroid peroxidase antibodies
D
Measurement of plasma renin activity and serum aldosterone
E
Reassurance and repeat thyroid function testing in 6 weeks

Cevap

Measurement of serum early morning cortisol

The patient's laboratory profile (a low Free T4 with an inappropriately normal TSH) is the hallmark of central hypothyroidism. His concurrent symptoms of weight loss, nausea, orthostatic hypotension, and hyponatremia strongly suggest concomitant central adrenal insufficiency (secondary to panhypopituitarism). Because the anterior pituitary regulates multiple endocrine axes, failure of one axis necessitates evaluation of the others. Crucially, in a patient with suspected panhypopituitarism, the adrenal axis must be evaluated (via early morning cortisol or an ACTH stimulation test) and treated before initiating thyroid hormone replacement. Giving levothyroxine accelerates the metabolic clearance of cortisol and can precipitate a fatal adrenal crisis in a cortisol-deficient patient.

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Interpret the thyroid function tests.

The TSH is inappropriately normal in the setting of a markedly low Free T4, which is the diagnostic hallmark of central (secondary) hypothyroidism.

A primary thyroid failure would lack negative feedback, resulting in an elevated TSH. A normal or low TSH indicates a pituitary or hypothalamic failure.

Correlate the thyroid findings with the rest of the clinical presentation.

The patient's weight loss, nausea, orthostatic hypotension, pale skin, and hyponatremia with normal potassium suggest concomitant central adrenal insufficiency.

The anterior pituitary regulates multiple axes. A destructive process (e.g., nonfunctioning macroadenoma) typically causes panhypopituitarism, affecting the thyrotrope, corticotrope, and gonadotrope axes together.

Determine the safest sequence for management.

The adrenal axis must be evaluated (with an early morning cortisol) and treated prior to replacing thyroid hormone.

Thyroid hormone replacement increases the basal metabolic rate and accelerates the hepatic clearance of cortisol. If given to a cortisol-deficient patient, it can rapidly deplete residual cortisol and precipitate a life-threatening adrenal crisis.

Anahtar Kavram

Diagnosis and management sequencing of panhypopituitarism (central hypothyroidism and central adrenal insufficiency)

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