Table 1. Mechanisms of pulmonary hypertension in systemic sclerosis.

World Health Organization group	Mechanism of pulmonary hypertension
1	•  Connective tissue disease-associated pulmonary arterial hypertension   •  Portopulmonary hypertension
1′	•  Pulmonary veno-occlusive disease   •  Pulmonary capillary hemangiomatosis
2	•  Myocardial fibrosis   •  Accelerated atherosclerosis   •  Kidney failure
3	•  Interstitial lung disease (combined pulmonary fibrosis and emphysema)
4	•  Venous thromboembolism/chronic thromboembolic pulmonary hypertension (antiphospholipid antibodies)