Step 1: Recall pathogenesis of oedema.
Oedema is abnormal accumulation of fluid in interstitial tissues. It results from imbalance of Starling forces and lymphatic drainage.
Step 2: Causes of oedema.
1. Decreased plasma oncotic pressure (A): Seen in hypoalbuminemia due to malnutrition, nephrotic syndrome, or liver disease. This reduces the pull of fluid back into capillaries.
2. Increased capillary permeability (B): Occurs in inflammation, burns, or allergy. Plasma proteins leak out, increasing fluid shift into tissues.
3. Obstruction of lymphatic drainage (D): Seen in filariasis, tumor compression, or surgical removal of lymph nodes. Prevents removal of interstitial fluid.
Step 3: Exclude wrong causes.
- (C) Increased plasma oncotic pressure: Does not cause oedema; it would prevent it.
- (E) Decreased capillary permeability: Not a cause of oedema; instead, it reduces fluid leakage.
Step 4: Conclusion.
The correct answer is A (Decreased plasma oncotic pressure), B (Increased capillary permeability), and D (Obstruction of lymphatic drainage).