Cushing Syndrome - Clinical Features

Guyton and Hall Textbook of Medical Physiology, 4th South Asia Edition

Definition

Causes

1. Pituitary adenoma - secretes excess ACTH → adrenal hyperplasia (most common)
2. Hypothalamic dysfunction - elevated CRH → excess ACTH release
3. Ectopic ACTH secretion - e.g., abdominal carcinoma, lung carcinoma
4. Adrenal cortex adenoma - primary cortisol overproduction (~20-25% of cases)
5. Iatrogenic - prolonged therapeutic use of large doses of glucocorticoids (e.g., in rheumatoid arthritis)

Clinical Features

1. Fat Redistribution (Characteristic Appearance)

• Buffalo hump - fat mobilized from the lower body is deposited in the thoracic and upper abdominal regions
• Moon face - excess steroid secretion causes an edematous, rounded facial appearance (see figure below)

Figure 78.11 - A patient with Cushing syndrome before (left) and after (right) subtotal adrenalectomy. Note the characteristic "moon face." (Courtesy Dr. Leonard Posey.)

2. Androgenic Effects

• Acne and hirsutism (excess facial hair) due to the androgenic potency of some adrenal steroids

3. Hypertension

• Present in about 80% of patients, attributed to the mineralocorticoid effects of the excess cortisol

4. Carbohydrate Metabolism - Steroid Diabetes

• Blood glucose may rise to 200 mg/dL after meals (nearly twice normal)
• Results from enhanced gluconeogenesis and decreased glucose utilization by tissues

5. Protein Catabolism Effects

• Profound protein catabolism throughout the body (except liver and plasma proteins)
• Muscle weakness - loss of protein from skeletal muscles
• Immune suppression - loss of protein synthesis in lymphoid tissues → high susceptibility to infections
• Purple (purplish) striae - subcutaneous collagen fibers are diminished, causing tissues to tear easily, visible as large purplish stretch marks
• Osteoporosis - severely diminished protein deposition in bones leads to weak, fragile bones

Summary Table