A thirty-five-year-old female is referred for endocrinologic evaluation due to progressive central weight gain, severe exhaustion, proximal muscle weakness, and easy bruising over the past seven months. Physical examination reveals a blood pressure of mm Hg, marked facial plethora, supraclavicular fat accumulation, and broad, violaceous abdominal striae. Arrange the following interventions in the most appropriate chronological sequence for the complete diagnostic workup and definitive management of this condition. Assume the patient ultimately has pituitary-dependent hypercortisolism, but any causative lesion identified on initial imaging is mm in diameter.
- 1Administer mg of dexamethasone at PM and measure serum cortisol the following morning at AM.
- 2Measure early morning plasma adrenocorticotropic hormone (ACTH) concentration.
- 3Obtain a high-resolution magnetic resonance imaging (MRI) scan of the pituitary gland.
- 4Perform bilateral inferior petrosal sinus sampling (IPSS) with corticotropin-releasing hormone (CRH) stimulation.
- 5Refer the patient for transsphenoidal pituitary exploration and tumor resection.
Answer
The correct sequence is: (1) 1-mg overnight dexamethasone suppression test, (2) Plasma ACTH measurement, (3) Pituitary MRI, (4) Inferior petrosal sinus sampling (IPSS), and (5) Transsphenoidal surgery.
The evaluation of Cushing syndrome requires a rigorous, stepwise approach to prevent diagnostic errors. First, endogenous hypercortisolism must be confirmed, typically using a 1-mg overnight dexamethasone suppression test, 24-hour urine free cortisol, or late-night salivary cortisol. Once confirmed, the next step is measuring plasma ACTH to determine if the disease is ACTH-dependent (normal/elevated ACTH) or ACTH-independent (suppressed ACTH). For ACTH-dependent disease, a pituitary MRI is performed. Because incidental, non-functioning pituitary microadenomas are common in the general population, finding a lesion smaller than 6 mm on MRI is insufficient for diagnosis. In such cases, bilateral inferior petrosal sinus sampling (IPSS) with CRH stimulation must be performed to definitively confirm that the pituitary is the source of excess ACTH (Cushing disease) rather than an ectopic source. Finally, once a central source is biochemically confirmed by a central-to-peripheral ACTH gradient, transsphenoidal surgical resection is the definitive treatment.
Step-by-Step Solution
Key Concept
The diagnostic algorithm for Cushing syndrome proceeds strictly from biochemical confirmation, to determining ACTH dependence, to anatomic localization, and finally to resolving imaging ambiguity with venous sampling before surgery.
Estimated Time:2m 30s