A -year-old female high school teacher presents to the clinic reporting progressive weight gain of kg over the past year, easy bruising, and new-onset facial hair growth. She also reports worsening fatigue and difficulty climbing stairs due to proximal muscle weakness. On examination, her blood pressure is mmHg. She exhibits prominent supraclavicular fat pads, facial plethora, and wide, purplish abdominal striae. A diagnostic evaluation for suspected hypercortisolism is initiated.
Arrange the following diagnostic tests in the most appropriate chronological sequence for evaluating this patient, from initial diagnostic screening to the most advanced localization study.
- 1-hour urine free cortisol assay
- 2Plasma adrenocorticotropic hormone (ACTH) measurement
- 3High-dose (-mg) dexamethasone suppression test
- 4Bilateral inferior petrosal sinus sampling (IPSS) for ACTH
Answer
The correct diagnostic sequence is: 1) -hour urine free cortisol assay to confirm hypercortisolism; 2) Plasma ACTH measurement to determine ACTH dependence; 3) High-dose dexamethasone suppression test to initially differentiate pituitary from ectopic sources; and 4) Bilateral inferior petrosal sinus sampling (IPSS) for definitive localization if non-invasive testing is equivocal.
The correct sequence adheres to the standard endocrine principles for evaluating suspected hormone excess: first, confirm the biochemical diagnosis of the hormone excess (urine free cortisol); second, identify the regulatory driver (plasma ACTH); third, localize the anatomical source through non-invasive dynamic testing (high-dose dexamethasone suppression); and fourth, proceed to invasive sampling (IPSS) only when non-invasive localization is inconclusive.
Step-by-Step Solution
Key Concept
The diagnostic algorithm for Cushing syndrome requires confirming hypercortisolism first, determining ACTH dependence second, and finally localizing the exact source using dynamic suppression tests followed by invasive venous sampling if needed.