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ACTH-Secreting Tumours : RCGP Curriculum Context

ACTH-secreting tumours, though rare in general practice, are an important topic in the RCGP curriculum due to their high clinical impact.


Basic Physiology of ACTH

Source & Regulation

  • Produced by: Anterior pituitary

  • Regulated by: Hypothalamic–pituitary–adrenal (HPA) axis

    • Corticotropin-releasing hormone (CRH) → stimulates ACTH release


Function

  • Target: Adrenal cortex (esp. zona fasciculata, reticularis)

  • Main effects:

    • ↑ Cortisol

    • ↑ Androgens (DHEA)

  • Mechanism: Via G protein-coupled receptors → ↑ cAMP in adrenal cells


Key Points: ACTH-Secreting Tumours

  • Cause ↑ ACTH → leads to Cushing’s syndrome.

  • Two main sources:

    • Pituitary adenomas (Cushing’s disease) – most common.

    • Ectopic ACTH-producing tumours – e.g. small cell lung carcinoma, carcinoid tumours.


  • Often presents with non-specific features (e.g. weight gain, HTN, mood changes) before diagnosis.


Domain Details
Presentation Central obesity, moon face, buffalo hump
Easy bruising, purple striae
HTN, T2DM, mood changes
Rapid onset with ↓ K⁺ → consider ectopic source
Red Flags Rapid symptom progression
Refractory HTN/hyperglycaemia
Severe hypokalaemia
Biochemistry ↑ Serum cortisol (loss of diurnal rhythm)
↑ Plasma ACTH
Low-dose dexamethasone suppression test: No suppression = Cushing’s present
High-dose dexamethasone suppression test:
• Pituitary: partial suppression → Cushing’s disease
• Ectopic: no suppression
Differentiation...

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