Ronan Doyle MVB CertSASMVB MRCVS CertSAS DipECVS RCVS & European Veterinary Specialist in Small Animal Surgery, Director at Davies Veterinary Specialists
Ronan Doyle is an entertaining speaker who breathed new life into an old dog of a condition, laryngeal paralysis in the dog.
Laryngeal paralysis is particulary topical at this time of year, the warm weather and dust of early summer seems often to be the trigger for acute episodes of respiratory distress. Ronan delighted the audience with a striking series of deep breathing noises which I think related to the subject!
So what’s already known? It affects any older larger breed dog, not just Labrador Retrievers. They present with inspiratory stridor, exercise intolerance, dyspnoea, collapse or cyanosis. The condition is progressive but if alveolar ventilation is compromised it must be treated as an emergency.
Ronan could not stress enough the importance of oxygen, and most interestingly only the smallest amount makes a massive difference – a mere 9% more inspired oxygen increases alveolar p02 by 20-30% in a compromised patient. That means you don’t even need to hold a mask to the face – in fact Ronan would positively discourage it. Use “flow-by” ventilation, not oxygen straight into the face! Other methods such as oxygen tents and the good old cling-filmed Buster collar are also good options.
Intravenous access for fluids would be sensible, particularly when hyperthermia is present. In such cases cooling with wet towels may also be required. One word of warning – as 10-20% of cases of laryngeal paralysis will also develop aspiration pneumonia, please make sure the hyperthermia is not actually pyrexia! Firstly the cooling won’t work, and secondly the 0.1mg/kg of intravenous dexamethasone you just gave it might just need an antibiotic chaser.
So what’s happening in the larynx? A quick anatomy lesson follows – don’t yawn, it’s quick and it’s clear. The inability to abduct the arytenoids and mucosal inflammation from turbulent airflow is demonstrated as the cause of the airflow obstruction; but why?
Well, mainly idiopathic, but very occasionally congenital, traumatic, neoplastic (mediastinal mass, thyroid tumour), iatrogenic (usually in cats following bilateral thyroidectomy, also secondary to external stabilisation of tracheal collapse in dogs).
However, what is now firmly accepted and increasingly understood is that most (if not all) dogs with acquired laryngeal paralysis have (or will develop) a generalised neuromuscular disease, with histological evidence of polyneuropathy. Oesophageal dysfunction is often also present at an early stage.
Michigan State University, bless them, have suggested “GOLPP” Geriatric Onset Laryngeal Paralysis Polyneuropathy (search GOLLP Michigan) as a more accurate description of the condition. Be quick, your clients will already know the term.
So on to diagnosis, and the accumulated wisdom of 30 years. Firstly, if it looks and sounds like laryngeal paralysis (based on signalment and a cough or change in bark) then it’s 96% likely that you are right!
Upper airway exam under sedation or light anaesthetic is not usually recommended as it presents an unnecessary increase in risk to the patient, unless preparation has been made to progress directly to surgery.
Symptomatic treatments and weight loss will improve patient comfort, but resolution will require surgery. The standard technique of unilateral arytenoid cartilage lateralisation has a >90% client satisfaction rating, but complications do arise such as bleeding, swelling and aspiration pneumonia.
On the subject of aspiration remember that many of these dogs have both laryngeal and oesophageal dysfunction. Liquid/sloppy or dusty foods should be avoided, and the entire front half of the dog can be elevated, not just the food bowl.
What we still don’t know: The cause of the polyneuropathy or any effective medical treatment. Michigan State is currently collecting DNA from hundreds of affected dogs, and will follow them in subsequent years. Watch this space!
The Stethoscope’s holiday stand-in (MRCVS)If you missed the live webinar it is now available to purchase at the link below http://thewebinarvet.com/webinar-archive/