A 42-year-old woman presents to her primary care physician with complaints of progressive weight gain, fatigue, and muscle weakness over the past six months. She has also noticed new stretch marks on her abdomen and has experienced increased facial hair growth. She reports irregular menstrual cycles and occasional headaches. Her medical history is significant for hypertension, which is managed with a thiazide diuretic. Vital signs are within normal limits except her blood pressure is 155/95 mm Hg. On physical examination, she has a rounded face with supraclavicular fat pads and purple striae on her abdomen. Laboratory results are as follows:
Which of the following is the most appropriate next step in evaluating this patient's condition?
B) Overnight low-dose dexamethasone suppression test
The patient presents with classic features of Cushing syndrome, including progressive weight gain, fatigue, muscle weakness, new stretch marks (striae), increased facial hair growth (hirsutism), hypertension, and hyperglycemia. The constellation of these symptoms suggests hypercortisolism.
The most appropriate next step in evaluating suspected Cushing syndrome is to confirm hypercortisolism using one of the first-line tests: late-night salivary cortisol assay, 24-hour urine free cortisol measurement, or overnight low-dose dexamethasone suppression test. The overnight low-dose dexamethasone suppression test involves administering dexamethasone at night and measuring serum cortisol levels the following morning. In normal individuals, dexamethasone suppresses cortisol production. Lack of suppression suggests hypercortisolism.
Answer choice A: Early-morning cortisol level, is incorrect. This test has limited utility in diagnosing Cushing syndrome due to significant overlap in cortisol levels between normal subjects and those with Cushing syndrome.
Answer choice C: Serum ACTH level, is incorrect. This test helps differentiate between ACTH-dependent and ACTH-independent causes of Cushing syndrome but is not the initial diagnostic step.
Answer choice D: Serum aldosterone to plasma renin activity ratio, is incorrect. This test evaluates for primary hyperaldosteronism, which presents with hypertension and hypokalemia, which does not represent the full clinical picture of Cushing syndrome.
Answer choice E: Serum testosterone level, is incorrect. The serum testosterone is elevated in some cases of Cushing syndrome due to increased adrenal androgen production but does not confirm hypercortisolism.
Key Learning Point
First-line tests for suspected Cushing syndrome include the: late-night salivary cortisol assay, 24-hour urine free cortisol measurement, or overnight low-dose dexamethasone suppression test.
