A 45-year-old woman presents to her primary care physician with complaints of chronic fatigue, unintentional weight loss, and episodes of dizziness over the past year. She also reports intermittent diarrhea and decreased appetite. Her medical history is significant for hypothyroidism for which she takes levothyroxine. Vital signs reveal a normal temperature, blood pressure of 90/60 mm Hg, pulse of 88/min, and respirations of 18/min. Physical examination reveals diffuse hyperpigmentation over her knuckles and elbows. Laboratory tests show the following:
Which of the following is the most appropriate next step in management of this patient?
B) ACTH stimulation test
The patient's symptoms of chronic fatigue, weight loss, dizziness, and hyperpigmentation, along with laboratory findings of hyponatremia, hyperkalemia, and a low-normal cortisol level, are suggestive of primary adrenal insufficiency (Addison disease). The most appropriate next step in management is to perform an ACTH stimulation test (cosyntropin test).
In the ACTH stimulation test, a synthetic ACTH analog (cosyntropin) is administered, and cortisol levels are measured before and after the injection. A normal response (cortisol level >20 μg/dL 30-60 minutes after cosyntropin administration) essentially rules out primary adrenal insufficiency. In patients with primary adrenal insufficiency, there will be a minimal or no increase in cortisol levels following cosyntropin administration due to the inability of the adrenal glands to respond.
Other options are less appropriate:
Answer choice A: 24-hour urine free cortisol, is incorrect. 24-hour urine free cortisol is used to evaluate for Cushing syndrome, not adrenal insufficiency.
Answer choice C: Insulin-induced hypoglycemia test, is incorrect. The insulin-induced hypoglycemia test is a complex and seldomly used test for adrenal insufficiency and pituitary function. The insulin-induced hypoglycemia test is used to determine how the hypothalamus, pituitary, and adrenal glands respond to stress. During this test, blood is drawn to measure the blood glucose and cortisol levels, followed by an injection of fast-acting insulin
Answer choice D: Intravenous hydrocortisone, is incorrect. Intravenous hydrocortisone can be used to treat acute adrenal crisis but not is not used for the initial diagnosis.
Answer choice E: Low-dose overnight dexamethasone suppression test is used to evaluate for Cushing syndrome and is not useful for diagnosing adrenal insufficiency.
Key Learning Point
For suspected primary adrenal insufficiency (Addison disease), indicated by chronic fatigue, weight loss, dizziness, hyperpigmentation, hyponatremia, and hyperkalemia, the ACTH stimulation test is an appropriate next step to confirm the diagnosis.
