A -year-old female patient presents to the primary care clinic reporting progressive weight gain, profound fatigue, and irregular menstrual cycles over the last year. On physical examination, her blood pressure is mm Hg. She has prominent facial adiposity, a dorsocervical fat pad, and multiple violaceous striae measuring up to cm in width across her lower abdomen.
The physician suspects an underlying endocrine disorder. Assuming each subsequent investigation result confirms the preceding suspicion and points toward a central etiology without definitive initial structural findings, arrange the following diagnostic steps in the correct clinical sequence to establish the diagnosis and identify the precise anatomical source.
- 1Measurement of 24-hour urinary free cortisol
- 2Measurement of plasma adrenocorticotropic hormone (ACTH) level
- 3Magnetic resonance imaging (MRI) of the pituitary gland
- 4Inferior petrosal sinus sampling (IPSS)
Answer
The correct sequence is: 1) Measurement of 24-hour urinary free cortisol, 2) Measurement of plasma ACTH level, 3) MRI of the pituitary gland, 4) Inferior petrosal sinus sampling (IPSS).
The diagnostic workup for Cushing syndrome must strictly follow a tiered physiological approach to prevent false-positive diagnoses and iatrogenic harm. First, endogenous hypercortisolism must be confirmed biochemically to ensure the patient's phenotype is truly due to excess cortisol. Second, measuring plasma ACTH determines whether the source is ACTH-dependent (pituitary or ectopic) or ACTH-independent (adrenal). Third, if the disease is ACTH-dependent, a pituitary MRI is obtained to search for an adenoma. Finally, if the MRI is negative or reveals a lesion smaller than 6 mm, IPSS is required to definitively measure gradients and distinguish between Cushing disease (pituitary source) and ectopic ACTH syndrome.
Step-by-Step Solution
Key Concept
The diagnostic evaluation of Cushing syndrome strictly proceeds from functional biochemical confirmation to hormonal dependency testing, followed by non-invasive anatomical imaging, and finally invasive localization if imaging is non-diagnostic.