Lecture Notes: Cushing's Syndrome

Introduction

• Presenter: Tom from Zero to Finals.
• Focus: Cushing's syndrome.
• Additional resources available at zerofinals.com and in the Zero to Finals Medicine book.

Overview of Cushing's Syndrome

• Definition: Features of prolonged high levels of glucocorticoids (e.g., cortisol) in the body.

Cortisol

• Type: Glucocorticoid steroid hormone.
• Produced by: Adrenal glands (above kidneys).
• Functions:
  • Stress response.
  • Increases alertness.
  • Inhibits the immune system and inflammation.
  • Inhibits bone formation.
  • Raises blood glucose levels.
  • Increases metabolism.
  • Supports cardiovascular function (increased heart rate, blood pressure, cardiac output).
• Release Pattern:
  • Pulses throughout the day.
  • Diurnal variation (high in the morning, low in the evening).

Hypothalamic Pituitary Adrenal Axis (HPA Axis)

• Components: Hypothalamus, pituitary gland, adrenal glands.
• Process:
  1. Hypothalamus releases CRH (corticotropin-releasing hormone).
  2. Anterior pituitary releases ACTH (adrenocorticotropic hormone).
  3. Adrenal glands release cortisol.
• Feedback Mechanism: Negative feedback suppressing CRH and ACTH when cortisol levels are high.

Causes of Cushing's Syndrome

• Mnemonic: CAPE:
  • C: Cushing's disease (pituitary adenoma, excess ACTH).
  • A: Adrenal adenoma (excess cortisol).
  • P: Paraneoplastic syndrome (ectopic ACTH, e.g., from small cell lung cancer).
  • E: Exogenous steroids (long-term corticosteroid use).

Distinguishing Cushing’s Disease from Cushing’s Syndrome

• Cushing's Disease: Specific case of a pituitary adenoma causing excess ACTH.

Clinical Features

• Physical Signs:
  • Round face (moon face).
  • Central obesity.
  • Abdominal stretch marks.
  • Buffalo hump (upper back fat pad).
  • Muscle wasting (thin arms and legs).
  • Male pattern facial hair in women.
  • Easy bruising, poor skin healing.
• Psychological Effects: Insomnia, anxiety, depression.
• Metabolic Effects:
  • Hypertension.
  • Cardiac hypertrophy.
  • Type 2 diabetes.
  • Dyslipidemia.
  • Osteoporosis.
• Skin Pigmentation: Indicative of high ACTH levels (e.g., pituitary adenoma).

Diagnostic Tests

• Dexamethasone Suppression Test:
  • Administer dexamethasone and monitor cortisol levels.
  • Used to determine the source of cortisol.
• Urinary Free Cortisol Test: 24-hour urine collection.
• Blood Tests and Imaging:
  • Blood counts, renal profile, MRI of brain (pituitary adenoma), CT scans (chest/adrenal tumors).

Treatment

• Surgical Options:
  • Transsphenoidal surgery for pituitary adenoma.
  • Removal of adrenal tumors and ectopic ACTH-secreting tumors.
  • Adrenalectomy when tumors cannot be removed.
• Medication: Metopirone to reduce cortisol production.

Study and Revision Tips

• Importance of the "testing effect" for memory retention.
• Practice recall to enhance learning outcomes.
• Zero to Finals offers various resources for exam preparation.