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Breeds predisposed to aspiration pneumonia | VETgirl Veterinary Continuing Education Podcasts

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In this VETgirl online veterinary continuing education podcast, we discuss whether certain breeds are more predisposed to aspiration pneumonia or not.

Do you see a lot of patients with respiratory signs in your practice? Do many of them have aspiration pneumonia? Aspiration pneumonia results from infection of the pulmonary parenchyma and alveoli due to entry of microorganisms into the lower respiratory tract during inhalation or aspiration. Predisposing factors include inability to protect the airway, which can be due to a number of causes including sedation, anesthesia, upper airway disease, neurologic impairment, esophagitis, vomiting, regurgitation, the list goes on.1

While a definitive diagnosis is generally based on some kind of airway sampling (e.g., broncho-alveolar lavage, endo- or transtracheal wash), many cases are diagnosed based on a compatible history and radiographic signs of an alveolar and/or interstitial lung pattern, often in the right middle, right cranial and caudal segment of the left cranial lung lobe(s).2

So, Greenwell et al out of Australia wanted to conduct a study called Aspiration pneumonia in the Irish wolfhound: a possible breed predisposition to evaluate if there were any breeds that were overrepresented with aspiration pneumonia. The authors felt like they were seeing a disproportionate number of Irish wolfhounds with aspiration pneumonia, and wondered if there might be some underlying predisposition to developing aspiration in the breed. So they retrospectively reviewed records from 2008-2012 to look at breed incidences of aspiration pneumonia.

So, what’d they find in this study?

In this study, canine patients were diagnosed with aspiration pneumonia based on radiographic findings (alveolar or interstitial pattern in dependent lung lobes), acute onset of clinical signs, and lack of other disease processes. Over the five year period, the overall incidence of aspiration pneumonia was 0.5%. Irish wolfhounds were the breed with the highest incidence of AP (9/25 dogs, 36%). The other breeds with the highest incidence of AP were Maremma sheepdogs (12.5%), Basset hounds (8.8%) and Bulldogs (6.4%). Of the 9 Irish wolfhounds with AP, 4 had an underlying cause identified: 1 had a choking episode, 1 had gastric dilatation, and 2 had laryngeal paralysis. The other 5 did not have a cause identified. None of the dogs have evidence of megaesophagus on thoracic radiographs. 8/9 dogs survived to initial discharge. Of the 5 dogs with unknown cause of their AP, 4/5 had recurrences of AP, 2 of which were ultimately euthanized.

So, what can we take away from this VETgirl podcast?
This study suggests the incidence of AP is increased in Irish wolfhounds. Since the study was retrospective, complete diagnostics weren’t done on all of the dogs – none had cardiac evaluations, and only one had a BAL. These limitations make it difficult to completely assess these cases, but their presumptive diagnosis of AP is reasonable based on established criteria. While a previous study has shown that megaesophagus was the most common cause of AP, none of the dogs in this study had evidence of megaesophagus on thoracic radiographs.3 The authors suggest that subclinical laryngeal paralysis may be present in this breed and may be a predisposing factor for AP.

Limitations of this study include its retrospective nature, small case numbers and lack of complete clinical work-up for all of the cases. That being said, this paper is the first to report on a potential predisposition to AP in Irish wolfhounds and as such, is important to be aware of.

Overall, this study suggests that AP may be more likely in Irish Wolfhounds, and should be considered in patients with acute onset of even mild respiratory signs. A complete evaluation should include examination of laryngeal function in this breed. If you see an Irish wolfhound with respiratory signs, aspiration pneumonia should be near the top of your differential list.

References:
1. Barton L. Aspiration pneumonia. In: Textbook of respiratory Disease in Dogs and Cats. Ed LG King. Saunders, St. Louis, MO, 2004: 422-430.
2. Tart MT, Babski DM, Lee JA. Potential risks, prognostic indicators and diagnostic and treatment modalities affecting survival in dogs with presumptive aspiration pneumonia: 125 cases (2005-2008). J Vet Emerg Crit Care 2010;20:319-329.
3. Kogan DA, Johnson LR, Sturges BK et al. Etiology and clinical outcome in dogs with aspiration pneumonia: 88 cases (2004-2006). J Am Vet Med Assoc 2008;233,1748-1755.
4. Greenwell CM, Brain PH. Aspiration pneumonia in the Irish wolfhound: a possible breed predisposition. J Sm Anim Prac 2014;55:515-520.

Abbreviations:
AP: aspiration pneumonia

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