Regional pulmonary veno-occlusion: a newly identified lesion of equine exercise-induced pulmonary hemorrhage.
Authors: Williams K J, Derksen F J, de Feijter-Rupp H, Pannirselvam R R, Steel C M, Robinson N E
Journal: Veterinary pathology
Summary
# Exercise-Induced Pulmonary Haemorrhage: A Veno-Occlusive Mechanism Although exercise-induced pulmonary haemorrhage (EIPH) affects up to 75% of racing Thoroughbreds and Standardbreds, its underlying pathophysiology remains poorly understood. Williams and colleagues examined lung tissue from seven racehorses with EIPH, collecting samples systematically from six regions per horse (84 sites total) and assessing them histologically for fibrosis, iron accumulation, vascular wall thickness, and angiogenesis. Whilst 46% of sections showed no pathological changes, the remaining 54% demonstrated progressive lesions, with 14% of samples—predominantly from the caudodorsal lung—exhibiting severe veno-occlusive remodeling of intralobular veins alongside haemosiderin deposition, fibrosis, and bronchial neovascularization. The authors propose that regional venous remodeling obstructs normal blood drainage from these areas, creating vascular congestion that culminates in haemorrhage, chronic iron deposition, and tissue scarring. For practitioners, these findings suggest that EIPH may represent a progressive vascular pathology rather than acute capillary fragility alone, potentially influencing how we assess, manage, and monitor high-performing horses, particularly regarding exercise prescription and the use of therapies targeting vascular integrity and pulmonary blood flow dynamics.
Read the full abstract on PubMed
Practical Takeaways
- •EIPH involves discrete regional venous remodeling in the back of the lungs rather than uniform pulmonary damage, which may explain variable clinical responses to management strategies
- •Understanding that hemorrhage leads to cumulative fibrosis and vascular remodeling suggests early intervention before chronic changes develop may be important for racehorses with recurrent bleeding
- •The focal dorsocaudal distribution of severe lesions could eventually inform targeted diagnostics or therapeutics once imaging/detection methods are refined
Key Findings
- •Regional veno-occlusive remodeling of intralobular veins was identified in the caudodorsal lung fields of 7 racing Thoroughbreds with EIPH, affecting 14% of sampled lung sections severely
- •Veno-occlusive lesions colocalized with hemosiderosis, fibrosis, pleural hypertrophy, and bronchial neovascularization in affected lung regions
- •46% of lung sections were histologically normal while 39% showed mild-to-moderate changes, indicating EIPH lesion distribution is highly regional and variable
- •Proposed mechanism links venous remodeling to regional vascular congestion, hemorrhage, and secondary fibrotic and angiogenic changes in the lung