What are the causes of pulmonary veno‑occlusive disease (PVOD)?

Causes of Pulmonary Veno-Occlusive Disease (PVOD)

PVOD occurs through three main pathways: heritable genetic mutations (bi-allelic EIF2AK4 mutations), associated conditions (systemic sclerosis, HIV infection), and exposure to specific drugs/toxins (cyclophosphamide, mitomycin, organic solvents). 1

Genetic Causes

Heritable PVOD is caused by bi-allelic mutations in the EIF2AK4 gene, which encodes a serine-threonine kinase that regulates gene expression in response to amino acid deprivation. 1 This represents a critical distinction from other forms of pulmonary arterial hypertension:

• Inheritance pattern: Autosomal recessive transmission—typically affects young siblings in one generation with unaffected parents 1
• Prevalence in familial cases: EIF2AK4 mutations are present in ALL familial PVOD/PCH cases 1
• Prevalence in sporadic cases: Found in 25% of histologically confirmed sporadic PVOD 1, 2
• Diagnostic significance: Identification of bi-allelic EIF2AK4 mutation is sufficient to confirm diagnosis without requiring hazardous lung biopsy 1

Notably, BMPR2 mutations (common in idiopathic PAH) are rarely found in PVOD patients, distinguishing it genetically from other PAH forms. 1

Associated Conditions

PVOD may complicate the course of several systemic diseases:

• Connective tissue diseases, particularly systemic sclerosis (SSc) 1
• HIV infection 1
• Portal hypertension (implied in classification structure) 1

The association with systemic sclerosis is particularly important, as venous and capillary involvement (PVOD-like features) is relatively common in connective tissue disease-associated PAH. 3

Drug and Toxin Exposures

Specific chemotherapeutic agents and occupational exposures are established PVOD triggers:

Chemotherapy agents:

• Cyclophosphamide 1
• Mitomycin (mitomycin-C) 1, 4, 5

Occupational/environmental exposures:

• Organic solvents 4, 3, 6
• Tobacco smoking (28% of cases in systematic review) 5

These exposures represent modifiable risk factors and should be specifically queried in the clinical history. The systematic review by 5 found smoking was the most frequent association (28%), followed by systemic sclerosis (10%) and mitomycin exposure (9%).

Idiopathic Cases

Approximately 75% of sporadic PVOD cases remain idiopathic after excluding EIF2AK4 mutations, associated conditions, and known exposures. 1, 2 The true incidence remains unknown as many cases are misclassified as idiopathic PAH—likely around 10% of presumed idiopathic PAH actually represents PVOD/PCH. 1

Clinical Pitfalls

Critical distinction from PAH: While PVOD shares hemodynamic similarities with PAH (precapillary pulmonary hypertension with normal wedge pressure), the underlying venous/capillary pathology makes standard PAH vasodilator therapy potentially life-threatening due to risk of acute pulmonary edema. 1, 4, 3 This makes accurate etiologic diagnosis essential before initiating therapy.

Male predominance: Unlike idiopathic PAH which affects more females, PVOD shows male predominance. 1