Pulmonary Hypertension (PH)
Pulmonary hypertension is defined as a mean pulmonary artery pressure $\geq 20$ mmHg. It is classified into five groups based on etiology, which is essential for management decisions.
1. WHO Classification Groups
- Group 1 (PAH): Pulmonary arterial hypertension (e.g., idiopathic, genetic BMPR2 mutation, drugs, connective tissue disease).
- Group 2: PH due to left heart disease (most common).
- Group 3: PH due to lung disease/hypoxia (e.g., COPD, ILD).
- Group 4: PH due to chronic thromboembolic disease (CTEPH).
- Group 5: PH with unclear/multifactorial mechanisms.
2. Pathogenesis and Morphology
Severe pulmonary hypertension leads to characteristic vascular remodeling:
| Feature | Description |
|---|---|
| Medial Hypertrophy | Smooth muscle thickening in small arteries and arterioles. |
| Plexiform Lesions | Tuft-like clusters of capillaries are found in severe, advanced cases (hallmark of Group 1). |
3. Exam Must-Knows
- Clinical Consequences: Elevated right-sided pressure leads to right ventricular hypertrophy (RVH), eventually resulting in cor pulmonale (right-sided heart failure).
- BMPR2 Mutation: Associated with hereditary PAH. Pathogenesis involves dysfunctional signaling in vascular smooth muscle cells, leading to excessive proliferation.
- Presentation: Exertional dyspnea, fatigue, syncope, and signs of right heart failure (e.g., jugular venous distention, peripheral edema).
Pathology Board Hint: For board questions, remember that Group 1 PAH in a young female is often idiopathic or associated with connective tissue diseases like scleroderma. Look for the “plexiform lesion” as a histological buzzword for severe pulmonary vascular remodeling.