ACVIM Asthma Consensus statement 2017

Overview of ACVIM Consensus Statements

• Consensus Statements by the American College of Veterinary Internal Medicine (ACVIM) deliver updated information on important animal diseases in the veterinary field.

• The selection of topics and the integrity of the draft process are overseen by the ACVIM Board of Regents.

• Evidence-based medicine is prioritized; interpretive comments are provided where evidence is insufficient or conflicting.

• Drafts solicit input from ACVIM members before being submitted to the Journal of Veterinary Internal Medicine for publication.

• Authors hold sole responsibility for the content of the statements.

Inflammatory Airway Disease (IAD) in Horses

Purpose of the Manuscript

• Revises and updates previous consensus statements on Inflammatory Airway Disease (IAD) in horses.

• Significant evolution in understanding since the last update in 2007 due to numerous scientific publications.

Key Terms and Definitions

• IAD (Inflammatory Airway Disease): A condition affecting horses with subtle symptoms that differ from more severe conditions like recurrent airway obstruction (RAO).

• Heaves: Severe airway obstruction characterized by increased coughing and respiratory effort, primarily observed in older horses.

Clinical Signs and Consequences

• Horses with heaves (RAO): Exhibit marked lower airway inflammation, frequent coughing, increased respiratory effort at rest, and exercise intolerance.

• IAD symptoms: Include poor performance and occasional coughing, often without significant changes in breathing at rest.

• Mucus Accumulation: Excessive mucus is characteristic of both conditions.

Comparisons to Human Conditions

• IAD and RAO are akin to asthma in humans, depicting a spectrum of chronic airway inflammation.

• Suggestion to categorize affected horses under the term “equine asthma syndrome.”

Diagnostic Confirmation

• Clinical Presentation: IAD affects horses of all ages, but most common in younger horses with symptoms of poor performance or chronic coughing.

• Diagnostic Tests: Airway endoscopy and bronchoalveolar lavage fluid (BALF) cytology are critical for diagnosing IAD.

  • Endoscopy: Excess tracheobronchial mucus scoring is essential for diagnosis.

  • BALF: Indicates mild increases in neutrophils, eosinophils, and other cell types.

Exclusion Criteria for IAD

• Signs of systemic infections, increased respiratory effort at rest, and other differentials must be ruled out to confirm IAD diagnosis.

Pathogenesis of IAD

• The underlying cause of IAD is not fully understood; non-infectious agents significantly contribute.

• Horses in stabling environments are often exposed to high airborne particle concentrations from dust, mold, and endotoxins.

• The innate immune response involves the activation of pro-inflammatory cytokines, with different cell types showing variable responses.

Inflammatory Response Variations

• IAD symptoms and severity may vary among horses; eosinophilic response is more common in younger horses, while neutrophilic IAD is more prevalent in older horses.

Diagnostic Methods

• Diagnosis relies on clinical signs, endoscopic findings of mucus, and BALF cytology results:

  • Mucus Scoring System: Scores range from 0 (no visible mucus) to 5 (profuse amounts of mucus).

  • Higher mucus scores indicate a higher prevalence of IAD, especially in young racehorses.

BALF Cytology

• Evaluation of BALF for neutrophils, eosinophils, and mast cells to confirm IAD.

• Reference ranges exist, but values should be interpreted based on the history and clinical findings.

Treatment Approaches for IAD

• Medical Treatment: Primarily focuses on environmental management and decreasing lung inflammation through glucocorticoids and bronchodilators.

  • Corticosteroids: Systemic glucocorticoids like dexamethasone and inhaled forms such as fluticasone are common treatments.

  • Bronchodilators: Aim to provide symptomatic relief by reducing airway hyperresponsiveness and mucus accumulation.

  • Mucolytics: Used to manage mucus clearance despite limited evidence for efficacy.

Management and Prevention Strategies

• Reducing exposure to airborne dust through dietary and stabling changes is crucial for management.

  • Switching to low-dust feed and improving barn ventilation can alleviate symptoms.

  • Environmental controls, like soaking hay and improving stable designs, can help mitigate triggers.

Future Research Directions

• Explore prevalence and phenotypes of IAD in various equine populations.

• Investigate relationships between coughing, mucus, and inflammatory markers in lower airways, and assess systemic biomarkers for diagnosis.

• Assess the effects of environmental management and treatment effectiveness through controlled trials.

Acknowledgments

• Acknowledged contributions and potential conflicts of interest by the authors related to commercial consulting and research related to the consensus statement topics.

References

• Detailed reference list of studies and evidence supportive of the statements made regarding IAD.