A 42-year-old woman is evaluated in the clinic due to progressive fatigue, constant chilli… — USMLE Step 2 CK

A $42$ -year-old woman is evaluated in the clinic due to progressive fatigue, constant chilling, and a $6$ -kg ( $13.2$ -lb) weight gain over the past $6$ months. She also reports worsening shortness of breath when climbing stairs, frequent morning headaches, and a tendency to bump into objects on her sides. She has not had a menstrual period in $8$ months. Her medical history is unremarkable, and she takes no medications. Vital signs show a temperature of $36.1^\circ$ C ( $97.0^\circ$ F), blood pressure of $88/58$ mmHg, pulse of $54$ /min, and respiratory rate of $14$ /min. Physical examination reveals a lethargic, pale woman with a delayed relaxation phase of the deep tendon reflexes. Visual field testing reveals bitemporal hemianopsia. She has non-pitting edema of the bilateral lower extremities. The lungs are clear to auscultation.

Laboratory studies reveal:
Sodium: $131$ mEq/L
Potassium: $4.1$ mEq/L
Creatinine: $0.8$ mg/dL
Thyroid-stimulating hormone (TSH): $1.1$ $\mu$ U/mL (Normal: $0.4$ – $4.0$ $\mu$ U/mL)
Free thyroxine (T4): $0.4$ ng/dL (Normal: $0.9$ – $2.4$ ng/dL)

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

A
Initiation of daily oral levothyroxine
Measurement of serum cortisol levelAnswer
C
Administration of intravenous furosemide
D
Arterial blood gas analysis
E
Initiation of empiric broad-spectrum antibiotics

Answer

The correct answer is measurement of a serum cortisol level.

The patient's clinical presentation (headaches, bitemporal hemianopsia, amenorrhea) and laboratory findings (low free T4 with an inappropriately normal TSH) strongly suggest a pituitary macroadenoma causing panhypopituitarism. In patients with suspected central hypothyroidism, concurrent central adrenal insufficiency is highly likely, supported here by her hypotension and hyponatremia. The essential next step is to evaluate the adrenal axis with a serum cortisol level. Initiating thyroid hormone replacement before confirming and treating adrenal insufficiency can rapidly increase cortisol clearance and precipitate a life-threatening adrenal crisis.

Step-by-Step Solution

Identify the primary endocrine disturbance from laboratory results.

The patient has a low free T4 level with an inappropriately normal TSH level, which is diagnostic of central (secondary) hypothyroidism.

Primary hypothyroidism would present with an elevated TSH level in response to low free T4.

Correlate with clinical findings to determine the underlying etiology.

Symptoms of morning headaches and bitemporal hemianopsia indicate a mass lesion compressing the optic chiasm, most likely a pituitary macroadenoma causing panhypopituitarism.

Amenorrhea (hypogonadism), hypotension, and hyponatremia further support multiple anterior pituitary hormone deficiencies, including gonadotropins and ACTH.

Determine the safest sequence of medical management.

Before starting thyroid hormone replacement for central hypothyroidism, the adrenal axis must be evaluated with a serum cortisol level.

Levothyroxine increases the basal metabolic rate and hepatic clearance of cortisol, which can precipitate a fatal adrenal crisis in a patient with untreated central adrenal insufficiency.

Key Concept

In patients with suspected central hypothyroidism or panhypopituitarism, the adrenal axis must be evaluated (and treated if necessary) prior to initiating thyroid hormone replacement to prevent precipitating an acute adrenal crisis.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic