A patient on long-term steroid therapy presents with centripetal obesity, buffalo hump, and abdominal striae. Dexamethasone suppression test confirms the diagnosis. What is the next investigation to identify the source?

1. A

   A. ACTH level

2. B

   B. CECT adrenal

3. C

   C. Non-contrast CT adrenal

4. D

   D. MRI pituitary gland

Appeared in: INI-CET EXAM -2026

Explanation

• After confirming the diagnosis of Cushing's syndrome (hypercortisolism), the very next step is to determine if the cause is dependent on or independent of Adrenocorticotropic Hormone (ACTH).
• Measuring the plasma ACTH level is the pivotal test for this differentiation.
• A low ACTH level points towards an adrenal source (ACTH-independent), while a normal or high ACTH level points towards a pituitary or ectopic source (ACTH-dependent).
• The result of the ACTH test dictates all subsequent imaging studies, making it the correct and most logical next investigation.

Why Other Options Were Wrong

• Option B: Adrenal imaging (CECT or non-contrast CT) is not the initial next step. It is only performed after a low ACTH level has confirmed an ACTH-independent (adrenal) cause.
• Option C: Similar to CECT, a non-contrast CT of the adrenal glands is only indicated after biochemical tests (specifically, a low ACTH level) point towards an adrenal pathology.
• Option D: Pituitary imaging is not the first step after confirming Cushing's syndrome. It is performed only after a normal or high ACTH level suggests a pituitary source (Cushing's disease).

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Diagnostic workup of Cushing's syndrome to guide bedside assessment, documentation, and the next nursing action.
• Following the correct diagnostic sequence in endocrinology is critical. Performing imaging before biochemical tests can lead to incorrect diagnoses due to the high prevalence of 'incidentalomas' (non-functional tumors found incidentally) in both the adrenal and pituitary glands.
• A nurse's role includes ensuring that samples for hormone levels like ACTH are collected at the correct time and under the right conditions, as levels can fluctuate.
• Patient education is key. A nurse may need to explain the rationale for the sequence of tests to the patient, reinforcing why a blood test must precede imaging.

How to Approach the Question

• First, identify the core of the question: it asks for the next step in the diagnostic process after Cushing's syndrome has already been confirmed.
• Recall the standard diagnostic algorithm for Cushing's syndrome. The algorithm is a stepwise process.
• Recognize that the first step after confirming hypercortisolism is to classify the cause. The primary classification is ACTH-dependent versus ACTH-independent.
• Identify the specific laboratory test used for this classification, which is the plasma ACTH level.
• Evaluate the options. The ACTH level (Option A) is the test that determines the next branch of the algorithm.
• Eliminate the imaging options (B, C, and D) because they are performed after the ACTH level is known and has guided the clinician toward a specific location (adrenal or pituitary).

Concept Tested & Keywords

• Concept Tested: Diagnostic workup of Cushing's syndrome
• Stem keywords: Cushing's syndrome, long-term steroid therapy, centripetal obesity, buffalo hump, abdominal striae, Dexamethasone suppression test, identify the source
• Lead-in keywords: next investigation
• Clinical cues: Patient has confirmed hypercortisolism and the goal is to find the source.

Question ID

QzFkEJEHkJh1Gd54D5piGW

Copy ID

Reference Book

E6 Medicine Harrison 22e Part 2 pp. 961-963, 915-917

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 1283-1285