Cushing syndrome in children — structured clinical encounter

Station brief (candidate)

You are the paediatric registrar. A 13-year-old girl presents with eight months of weight gain, a round face, purple abdominal striae and fatigue, plus worsening mood and falling school marks. Her weight has risen beyond the 95th centile while her height has crossed from the 50th to the 10th, and her blood pressure is 142 over 90. The team asks you to make the diagnosis, arrange the investigations, plan the treatment, and speak with the family. You have 12 minutes with the team and 5 minutes for examiner discussion. [1]

Information available on request

• 13-year-old girl; weight gain, moon face, broad purple striae over abdomen and thighs, easy bruising, fatigue over eight months. [1]
• Growth chart: weight 75th centile to beyond 95th; height 50th centile crossing down to 10th; bone age advanced. [9]
• Blood pressure 142 over 90 (elevated for age); proximal muscle weakness on standing from a squat; delayed puberty. [1]
• Parents anxious and ask whether this is "just obesity" and whether it can be treated. [9]

Tasks

1. State the most likely diagnosis and the single bedside feature that distinguishes it from simple obesity. [1]
2. Outline the confirmatory biochemical work-up, naming the three first-line tests and why at least two are used. [3]
3. Describe the localising step after cortisol excess is confirmed, including the role of inferior petrosal sinus sampling. [5]
4. State the first-line definitive treatment and the perioperative medication that is mandatory after cure, and communicate the plan in plain language to the family. [6]

Marking anchors

Must-hit

• Diagnoses Cushing syndrome (most likely pituitary Cushing disease), with growth arrest — height crossing down while weight rises — as the discriminator from simple obesity, in which the child keeps growing. [1]
• Confirms with at least two of three tests: a late-night salivary or serum cortisol, a 24-hour urinary free cortisol, and an overnight dexamethasone suppression test (15 µg per kilogram capped at 1 mg; cortisol not suppressed below 1.8 µg per decilitre supports Cushing). [3]
• Localises by plasma ACTH, then pituitary MRI for ACTH-dependent disease, with bilateral inferior petrosal sinus sampling when the MRI is negative or non-lateralising (central-to-peripheral ACTH ratio above two at baseline or above three after corticotrophin-releasing hormone confirms pituitary disease). [5]
• Plans transsphenoidal selective adenomectomy as first-line, with mandatory perioperative stress-dose glucocorticoid because the cured child is adrenally insufficient, followed by replacement until axis recovery. [6]

Merit

• Explains that growth arrest occurs because cortisol suppresses the growth-hormone axis, and that final height may still be compromised despite cure, so early diagnosis is the biggest modifiable factor. [9]
• Counsels the family in plain language: this is not simple obesity, the cause is a treatable hormone excess, the operation aims to remove a small pituitary adenoma, and the child will need steroid tablets for months afterwards because her own system is suppressed. [6]
• Places the case in context: endogenous Cushing is rare in children, but the growth-chart pattern is unmistakable once plotted, and the disease is curable in the majority with expert surgery. [1] [9]

Fail

• Reassures the family that this is simple obesity and advises diet and exercise, missing the falling height velocity. [1]
• Orders a single random cortisol and concludes there is no disease, ignoring the need for two structured tests and the loss of the diurnal rhythm. [3]
• Plans surgery without arranging perioperative glucocorticoid cover, leaving the cured child to develop adrenal crisis. [4]