Table 1. Clinical classification of pulmonary hypertension.

1. Pulmonary arterial hypertension
	1.1 Idiopathic 1.2 Heritable 1.2.1 BMPR2 mutation 1.2.2 Other mutation 1.3 Drugs and toxins induced 1.4 Associated with: 1.4.1 Connective tissue disease 1.4.2 Human immunodeficiency virus (HIV) infection 1.4.4 Portal hypertension 1.4.4 Congenital heart disease 1.4.5 Schistosomiasis
	1′ Pulmonary Veno-occlusive disease and/or pulmonary capillary hemangiomatosis
	1′.1 idiopathic 1′.2 Heritable 1′.2 1 EIF2AK4 mutation 1′.2 2 Other mutation 1′.3 Drugs, Toxins and radiation induced 1′.4 Associated with: 1′.4.1 Connective tissue disease 1′.4.2 HIV infection
2. Pulmonary hypertension due to left heart disease
	2.1 Left ventricular systolic dysfunction 2.2 Left ventricular diastolic dysfunction 2.3 Valvular disease 2.4 Congenital/acquired left heart inflow/outflow tract obstruction and congenital cardiomyopathies 2.5 Congenital/acquired pulmonary veins stenosis
3. Pulmonary hypertension due to lung disease and/or hypoxia
	3.1 Chronic obstructive pulmonary disease 3.2 Interstitial lung disease 3.3 Other pulmonary disease with mixed restrictive and obstructive pattern 3.4 Sleep-disordered breathing 3.5 Alveolar hypoventilation disorders 3.6 Chronic exposure to high altitude 3.7 Developmental lung disease
4. Chronic thromboembolic pulmonary hypertension and other pulmonary artery obstruction
	4.1 Chronic thromboembolic pulmonary hypertension 4.2 Other pulmonary artery obstruction 4.2.1 Angiosarcoma 4.2.2 Other intravascular tumors 4.2.3 Arteritis 4.2.4 Congenital pulmonary arteries stenosis 4.2.5 Parasites (hydatidosis)
5. Pulmonary hypertension with unclear and/or multifactorial mechanisms
	5.1 Hematological disorders: chronic hemolytic anemia, myeloproliferative disorders, splenectomy 5.2 Systemic disorders: sarcoidosis, pulmonary histiocytosis, lymphangioleiomyomatosis, neurofibromatosis 5.3 Metabolic disorders, glycogen storage disease, Gaucher disease, thyroid disorders 5.4 Others: Pulmonary tumoral thrombotic microangiopathy, fibrosing mediastinitis, chronic renal failure (with/without dialysis), segmental pulmonary hypertension

Abbreviations: BMPR2, bone morphogenetic protein receptor, type 2; EIF2AK4, eukaryotic translation initiation factor 2 α kinase 4.

Source: Reproduced with permission from McLaughlin et al, circulation 2009, and Galie et al ERS/ESC Guidelines for diagnosis and treatment for pulmonary hypertension, Eur Heart J 2016. ^{4 5}