Are your veterinary patients coughing up a lung? Or is it a larynx?

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Coughing dogs are frequent visitors at almost any veterinary practice. The rule-out list can be exhaustive. When we work up a cough, we should consider all portions of the aerodigestive tract (larynx, pharynx, respiratory tract and digestive tract) and prioritize the diagnostics to try to get maximum “bang for the buck” for our clients. In doing so, you might think you can skip an endoscopic examination, but if you're not suggesting laryngoscopy or bronchoscopy for your coughing patients, how often are you missing something?

Cough = dysfunction?

A recently published study from the University of California, Davis, examined the role of laryngeal abnormalities in dogs that were presented because of cough. Dogs with other signs of upper airway disease were excluded. The investigator hypothesized that laryngeal dysfunction would exist in dogs presented for coughing. A single examiner performed laryngoscopic and bronchoscopic examinations on the 138 dogs included in the study, which took place from July 2001 to October 2014. Dogs were assigned into three groups based on the duration of their cough: acute (< two weeks), subacute (two weeks to two months) and chronic (> two months).

Dogs with an acute cough (4 dogs) were not observed to have laryngeal inflammation, but it was noted in more than half of the dogs with subacute and chronic coughing (73/138 dogs). Laryngeal function appeared normal in all acutely coughing dogs, but of the 30 dogs with cough of subacute duration, three had laryngeal paralysis and one had laryngeal paresis. Of the 104 dogs with chronic cough, 10 had laryngeal paralysis and 12 had laryngeal paresis.

At the end of the study, 83 of the 138 dogs (60%) had a final diagnosis of inflammatory airway disease. Of those 83 dogs, 60% also had concurrent airway collapse. Six of the 138 dogs (4%) had airway collapse alone, and 34 dogs (25%) had a lower respiratory tract infection. Six (18%) of the dogs with lower respiratory tract infection also had a foreign body.

Results indicate that dogs with a cough of more than two weeks' duration commonly have laryngeal swelling regardless of the underlying disease process. Laryngeal paralysis or paresis was also fairly common-seen in 19% (26/134) of the dogs with a cough of more than two weeks' duration. Interestingly, laryngeal disease was not suspected in any of the dogs in the study, but was identified by laryngoscopic examination in almost 19% (26/138) of the dogs.

Exam-room application

There has been a clear association between laryngeal dysfunction and aspiration pneumonia in previous studies,1-3 but this study wanted to investigate the prevalence of laryngeal abnormalities in dogs that did not present with clinical signs of an upper airway disease to help practitioners better decide the diagnostic pathway for such dogs. These findings indicate that an endoscopic examination of the respiratory tract should be considered in all dogs examined for cough lasting longer than two weeks because laryngeal disorders were discovered in a significant number.

Your clients might not be the first to jump at expensive diagnostics, but perhaps the awareness that laryngeal disease might be present in almost 20% of these chronic cough cases will help.

Johnson LR. Laryngeal structure and function in dogs with cough J Am Vet Med Assoc 2016;249(2):195-201.

Link to study: http://avmajournals.avma.org/doi/pdf/10.2460/javma.249.2.195

References:

1. MacPhail CM, Monnet E. Outcome of and postoperative complications in dogs undergoing surgical treatment of laryngeal paralysis: 140 cases (1985–1998). J Am Vet Med Assoc 2001;218:1949-1956.

2. Hammel SP, Hottinger HA, Novo RE. Postoperative results of unilateral arytenoid lateralization for treatment of idiopathic laryngeal paralysis in dogs: 39 cases (1996–2002). J Am Vet Med Assoc 2006;228:1215-1220.

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.