Classification of Primary Pulmonary Hypertension (PPH)

Primary Pulmonary Hypertension (PPH) represents Group 1 within the Pulmonary Hypertension (PH) WHO clinical classification system (Venice 2003 revision) and is one of five such groups. The groups are divided based on aetiology.

Group I.Primary Pulmonary Hypertension (PPH)
  • Idiopathic
  • Familial
  • Associated with:
    • Connective tissue disease
    • Congenital systemic-to-pulmonary shunts
    • Portal Hypertension
    • HIV infection
    • Drugs and toxins
    • Other (thyroid disorders, glycogen storage disease, Gaucher's disease, hereditary haemorragic telangiectasia, haemoglobinopathies, myeloproliferative disorders, splenectomy)
  • Associated with significant venous or capillary involvement
    • Pulmonary veno-occlusive disease (PVOD)
    • Pulmonary capillary haemangiomatosis (PCH)
  • Persistent pulmonary hypertension of the newborn (PPHN)
Group II.Primary Pulmonary Hypertension (PPH) associated with left heart diseases
Group III.Primary Pulmonary Hypertension (PPH) associated with respiratory diseases and / or hypoxemia (including chronic obstructive pulmonary disease)
Group IV.Primary Pulmonary Hypertension (PPH) due to chronic thrombotic and/or embolic disease
Group V.Miscellaneous group
  • eg. sarcoidosis, histiocytosis X and lymphangiomatosis

Ideopathic Primary Pulmonary Hypertension (PPH), which by definition has no identifiable underlying cause, is one of the more common types of Primary Pulmonary Hypertension (PPH). Familial PAH (FPAH) accounts for at least 6% of cases of IPAH and mutations in the bone morphogenetic protein receptor 2 (BMPR2) have been identified in the majority of cases of FPAH.

Primary Pulmonary Hypertension (PPH) can also be associated with a number of conditions (Associated Pulmonary Arterial Hypertension - APAH), which together account for most other cases of Primary Pulmonary Hypertension (PPH). These conditions include;

1.Connective Tissue Diseases
  • including systemic sclerosis (scleroderma) and systemic lupus erythematosus (SLE)
2.Congenital heart disease
  • including Eisenmenger's syndrome
3.Human immunodeficiency viruinfection
4.Sickle Cell Disease

Primary Pulmonary Hypertension (PPH) is also a rare side effect of certain anorexigenic agents, such as fenfluramine and dexfenfluramine. However, the incidence of drug-induced Primary Pulmonary Hypertension (PPH) is decreasing as these agents are no longer available.

1. Primary Pulmonary Hypertension (PPH) associated with connective tissue disease
Primary Pulmonary Hypertension (PPH) is a well-recognised complication of connective tissue diseases such as systemic sclerosis and SLE and in affected patients may also occur in association with Interstitial lung disease. The prevalence of Primary Pulmonary Hypertension (PPH) in patients with systemic sclerosis has been reported to be up to 16% and in systemic sclerosis patients, pulmonary complications, such as interstitial lung disease and Primary Pulmonary Hypertension (PPH), are now the leading causes of death. Patients with Primary Pulmonary Hypertension (PPH) associated with systemic sclerosis have a particularly poor prognosis compared to those with systemic sclerosis without Primary Pulmonary Hypertension (PPH).

2. Primary PulmonaryHypertension (PPH) associated with congenital heart disease
Congenital heart disease is relatively common, affecting around 1% of the population. Within this population 15% will go on to develop Primary Pulmonary Hypertension (PPH). As determined by the level of pulmonary vascular resistance, the most severe form of Primary Pulmonary Hypertension (PPH) is Eisenmenger's Physiology, which is associated with the reversal of an initial left to right shunt causing Cyanosis and limited exercise capacity.

3. Primary Pulmonary Hypertension (PPH) associated with HIV infection
Primary Pulmonary Hypertension (PPH) is a rare (estimated prevalence in patients with HIV: 0.5%) but relatively well-documented complication of HIV infection. With the advent of highly active anti-retroviral therapy (HAART) and markedly improved survival, Primary Pulmonary Hypertension (PPH) and other non-infectious manifestations of HIV infection are increasingly responsible for HIV-associated morbidity and poor prognosis. In patients with HIV, the HIV-1 envelope glycoprotein GP120 may stimulate the production of endothelin by macrophages. HIV-associated Primary Pulmonary Hypertension (PPH) shows a similar clinical picture to IPAH and seems to be independent of the degree of immunosuppression.

4. Primary Pulmonary Hypertension (PPH) associated sickle cell disease
The prevalence of Primary Pulmonary Hypertension (PPH) in patients with sickle cell disease is 20%-40%