Sudden death attributable to exercise-induced pulmonary hemorrhage in racehorses: nine cases (1981-1983).

This research article examines sudden death in racehorses during racing or training, focusing on nine cases between 1981 and 1983 where death was caused by exercise-induced pulmonary hemorrhage (EIPH). The study explores the pathological changes in the horses and suggests that conditions like small airway disease or bronchiolitis may contribute to fatal pulmonary hemorrhage.

Introduction and Study Overview

• The study aimed to investigate the cause of sudden deaths in racehorses, specifically focusing on cases where acute pulmonary hemorrhage was noted during exercise. The research sought to describe pathological changes that occur within such horses.
• This consisted of an analysis of 11 horses that passed away during racing or training exercises over a two-year period (1981-1983). The results found nine of these deaths were due to exercise-induced pulmonary hemorrhage. One horse succumbed to exsanguination, or severe blood loss, while another perished due to Central Nervous System (CNS) trauma.
• The research, therefore, concentrates mainly on the anatomy of EIPH, the biological sequence of events that lead to it, and identifies potential triggers for this phenomenon.

Findings and Observations

• No cardiac lesions were found in any of the horses, ruling out any heart anomalies as potential causes of death.
• All nine horses that died of EIPH exhibited severe engorgement of the pulmonary vessels with evidence of hemorrhaging into the alveoli, airways, interstitium and subpleural tissues.
• Further, six of the horses showed infiltration of eosinophils and/or lymphocytes around the vessels and airways, which is suggestive of local inflammation or an immune system response. This potentially suggests an ongoing underlying disease process.
• Six horses had focally extensive fibrosis observed in the pleura and interstitium, areas lining the chest wall and surrounding lung tissue. Collections of siderophages (cells that have absorbed excess iron) were spotted in the fibrous tissue and the airways, both potential indicators of chronic inflammation or earlier hemorrhagic episodes.
• Significant occlusion, or blockage, of bronchioles due to the thickening of mucus, was found in four horses. This condition is usually associated with small airway disease.

Conclusions and Implications

• The findings show that underlying respiratory tract lesions, particularly those associated with small airway disease or bronchiolitis, might contribute to fatal pulmonary hemorrhage in horses.
• Identifying these key pathological changes could lead to new prevention strategies and diagnostic tools for EIPH and may prevent sudden deaths in racehorses.
• Recognizing potential triggers, such as small airway disease or bronchiolitis, and treating these conditions before a horse engages in intense exercise, may lead to a decrease in EIPH incidents.