A -year-old woman comes to the clinic due to a -month history of profound fatigue, generalized weakness, and amenorrhea. She previously had regular, -day menstrual cycles. Over this period, she has had an unintentional weight loss of kg ( lbs). Her blood pressure is mmHg, and her pulse is /min. Physical examination shows pale skin without hyperpigmentation, a delay in the relaxation phase of the deep tendon reflexes, and decreased axillary and pubic hair. Laboratory studies show the following:
| Laboratory test | Result | Reference range |
|---|---|---|
| Sodium | mEq/L | mEq/L |
| Potassium | mEq/L | mEq/L |
| Thyroid-stimulating hormone (TSH) | U/mL | U/mL |
| Free thyroxine (T4) | ng/dL | ng/dL |
Which of the following is the most appropriate next step in management?
- Measurement of serum morning cortisolCevap
- BMeasurement of anti-thyroid peroxidase antibodies
- CInitiation of levothyroxine therapy
- DMeasurement of serum reverse triiodothyronine
- EMagnetic resonance imaging of the brain
Cevap
Measurement of serum morning cortisol
The correct answer is measurement of serum morning cortisol. This patient's presentation of fatigue, weight loss, amenorrhea, hypotension, hyponatremia, and loss of axillary/pubic hair is highly suspicious for panhypopituitarism. Her laboratory results show a low Free T4 with an inappropriately normal TSH, confirming central hypothyroidism. Because pituitary disease affects multiple hormonal axes, she likely also has secondary adrenal insufficiency (indicated by hypotension and hyponatremia; the normal potassium level is expected because aldosterone production is governed by the renin-angiotensin-aldosterone system, not ACTH). A critical rule in endocrinology is that thyroid hormone replacement (levothyroxine) accelerates cortisol metabolism and clearance. If levothyroxine is given to a patient with untreated adrenal insufficiency, it can precipitate a fatal adrenal crisis. Therefore, the adrenal axis must be evaluated with a morning cortisol level (or ACTH stimulation test) and treated with glucocorticoids before or simultaneously with levothyroxine.
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Anahtar Kavram
In patients with suspected panhypopituitarism (e.g., central hypothyroidism), secondary adrenal insufficiency must be biochemically ruled out or empirically treated with glucocorticoids before initiating levothyroxine therapy to prevent precipitating an adrenal crisis.