Feline lower airway disease: asthma and beyond

What is ‘asthma’?

The term ‘asthma’ is used in human medicine to describe a condition caused by spontaneous bronchoconstriction and airway remodelling, often presenting with dyspnoea, and responding to treatment with bronchodilators (Reinero et al, 2009a). In cats, although a subset of patients will present in this way, the majority have a chronic cough. To complicate the classification of non-infectious, inflammatory bronchial disease in cats, many have predominantly neutrophilic airway inflammation, or a mixed cell cytology on bronchoalveolar lavage (BAL). This is in contrast to the predominantly eosinophilic inflammation classically seen in feline asthma. Standardisation of terminology is not currently available and many consider non-infectious inflammatory bronchial disease in cats to be a spectrum (Rozanski, 2016), as illustrated in Figure 1, and in a clinical setting, without BAL, defining the underlying condition may not be possible.

Pathophysiology

In feline asthma it is generally accepted that a type 1 hypersensitivity reaction occurs within the airways, where sensitised cats react to repeat exposure to an antigen with mast cell degranulation. Histamine and leukotrienes result in increased vascular permeability and smooth muscle contraction (acute airway narrowing), eosinophils are recruited and worsen the inflammation and tissue damage (Corcoran et al, 1995). This inflammation results in airway hyper-reactivity, smooth muscle hypertrophy and excessive mucus production (Venema and Patterson, 2010). The condition is seen more commonly in young to middle-aged cats, with Siamese and other Oriental cats overrepresented (Foster at al, 2004b). Multiple triggering allergens are implicated, including dusty cat litter, house dust mites, strong chemical smells, building dust, perfumes, hairspray, cigarette smoke and pollens (Baral, 2012).

In chronic bronchitis neutrophilic inflammation predominates, with excessive mucus production and airway remodelling and narrowing. This condition does not seem to be acutely triggered by allergens or result in bronchoconstriction, but the causes are not fully understood (Venema and Patterson, 2010).

Reduced airflow occurs in both conditions due to oedema, mucus, inflammation and epithelial alterations, with bronchoconstriction occurring in cats with asthma. These changes in airway diameter, even if small, result in significant reductions in airflow. Over time changes become permanent including fibrosis and emphysema.

The role of mycoplasmas (small bacterial organisms) in feline respiratory disease has been studied in cats and remains unclear. The organisms are found as commensals in the upper respiratory tract, but have been associated with lower airway disease, where they may not be the primary cause, but are likely an exacerbating factor (Lee-Fowler, 2014). Testing for, and treating Mycoplasma spp. infection is therefore generally advised for cats with lower airway conditions.

Clinical signs of lower airway disease

Asthma and chronic bronchitis result in a chronic cough, due to airway narrowing, mucus, and direct effects of inflammation on mechanoreceptors in the airways. Owners may mistake this cough for a retch, or conclude something is stuck in the cat's throat, for example a hairball. Cats at the asthma end of this disease spectrum are more likely to develop respiratory distress and particularly expiratory dyspnoea, with increased effort on exhalation compared with inspiration. Exercise intolerance is hard to spot in cats compared with dogs, but affected cats may be lethargic, or become tachypnoeic after playing. Signs may be episodic, persistent or intermittent (Corcoran, 1995). On physical examination affected cats may have an expiratory wheeze or crackles, and if in respiratory distress they may be cyanotic.

Diagnosis

Importantly cats with lower airway disease can make fragile patients, decompensating and suffering a respiratory arrest if handled inappropriately. Although diagnostic tests are important, emergency treatment of dyspnoeic cats should be ‘hands off ’ and tests requiring restraint such as radiography postponed until the cat is more stable. Veterinary nurses play a vital role in the careful and calm handling of dyspnoeic cats to avoid deterioration.

Clinical signs and physical examination findings may be consistent with lower airway disease, but differential diagnoses such as congestive heart disease, lungworm, pleural space disease or upper respiratory disease must be excluded. Tests will be dictated by the individual case, but blood tests are generally unremarkable, with circulating eosinophils found in around 20% of cats with asthma (Rozanski, 2016). Faecal analysis may be indicated to exclude feline lungworm (Aelurostrongylus abstrusus).

Diagnostic imaging

Radiography is important in the diagnosis of lower airway disease and usually reveals a diffuse bronchial, or bronchointerstitial pattern (Figure 2) (Gadbois et al, 2009), although radiographs may be normal. Other abnormalities include lung hyperinflation, hyperlucency, right middle lung lobe collapse and aerophagia.

Thoracic computed tomography (CT) is growing in popularity in veterinary medicine and in cases of lower airway disease it can reveal airway thickening, lung lobe consolidation and mucus accumulation, and exclude other differential diagnoses (Figure 3).

Bronchoscopy and BAL

Bronchoscopy (Figure 4) with BAL is useful in the diagnosis of lower airway disease in cats, as collection of BAL samples allows cytology and testing for infectious agents to be performed. BAL samples can be collected via the bronchoscope, or blindly. Contraindications include severe dyspnoea/hypoxia, coagulopathy or cats with very unstable asthma. Bronchoscopy of asthmatic cats is associated with severe bronchospasm, but pre-treatment with terbutaline (a bronchodilator), and using saline at body temperature for the wash may help prevent this complication (Kirschvink et al, 2005).

Equipment for BAL

It is desirable to keep anaesthesia time to a minimum by preparing equipment before induction. Have available:

During the procedure the tube, or bronchoscope is passed distally to form a seal inside a bronchus and a wedge of lung isolated, before instilling the aliquots of sterile saline followed by aspiration. A frothy sample suggests surfactant and a successful BAL.

Anaesthetic monitoring

Monitoring under anaesthesia is commonly a nurse's job. Recording observations on an anaesthetic chart is important to identify trends and document the procedure. Monitor respiratory rate and pattern, oxygen saturation with a pulse oximeter, heart rate and temperature. If available an ‘elbow port’ (Veterinary Instrumentation) can be used to provide oxygen and a volatile anaesthetic agent during lavage. Saturation should be maintained at >95% throughout the procedure, and 100% oxygen supplied before, and immediately after samples have been taken for 3–5 minutes, and the cat closely observed for signs of hypoxia (shallow, rapid breathing, SpO₂ < 95%) (Hibbert, 2013).

Complications also occur in the post-anaesthetic period when cats should be closely monitored for complications. Key points include:

Other complications can include pneumothorax and haemorrhage, thankfully rarely seen.

Sample handling

Ideally samples are analysed within 24 hours, which can be hard to achieve in general practice, so tubes may need refrigeration or smears preparing (Venema and Patterson, 2010). Discuss with the laboratory how to handle samples to maximise diagnostic yield. An EDTA sample should be collected for cytology, and an additional plain or EDTA sample submitted for Bordetella and Mycoplasma polymerase chain reaction (PCR).

Management of cats with lower airway disease

Emergency treatment

As mentioned, dyspnoeic cats are prone to decompensation so a ‘less is more’ approach should be adopted and thought given to stress reduction. Box 1 lists the appropriate approach to cases of feline lower respiratory disease presenting with dyspnoea. Note that other common causes of dyspnoea such as congestive heart failure and pleural effusion should be excluded.

Box. 1

Emergency treatment of the dyspnoeic cat

Prepare prior to the cat's arrival if possible with a crash box/trolley, endotracheal tubes (ET) tubes (in a range of sizes), anaesthetic machine and ready an oxygen cage

Avoid stress as a priority; handling should be minimised (Figure 5) and sedation with butorphanol may be indicated, keep the cat quiet and away from dogs, but where it can be monitored closely

Oxygen supplementation should be provided immediately, ideally using an oxygen cage or tent to reduce the need for handling or restraint

Ideally an intravenous catheter is placed to allow for emergency treatment and resuscitation if required, but should be done without causing distress

Diagnostic tests, such as radiography, should be performed only once the cat is stable and with the cat in sternal recumbancy. Ultrasound is useful for excluding other causes of acute dyspnoea (e.g. pleural effusion) and may be less stressful for the cat

If clinical signs are consistent with lower airway disease (rather than other common causes of dyspnoea such as pleural effusion and congestive heart failure) then treatment with a bronchodilator (e.g. terbutaline intramuscularly (IM) or intravenously (IV) or inhaled salbutamol) is indicated along with an antiinflammatory dose of corticosteroid (hydrocortisone or dexamethasone)

Chronic therapy

The mainstay of treatment of lower airway disease is corticosteroid treatment, but bronchodilator therapy can be helpful for cats with bronchoconstriction. As treatment is life-long and potentially associated with side effects, other causes of airway disease should be excluded and treated empirically if necessary, such as antiparasitic treatment for lungworm. Clients should also be counselled as to maintaining their cat at a healthy weight and overweight or obese cats should be seen in a weightmanagement clinic at the practice to encourage slow, healthy weight loss.

Removal of triggers: cigarette smoke and dusty cat litters should be avoided, owners should vacuum daily to remove house dust mites, and high-efficiency particulate air filters may be helpful for indoor cats.

Corticosteroid therapy forms the mainstay of management of affected cats. Oral prednisolone is used initially in most cases, using dosages to control clinical signs (0.5–1.0 mg/kg twice daily (BID)), but tapered to avoid side effects such as polydipsia and insulin resistance resulting in diabetes mellitus (Rozanski, 2016). Injectable corticosteroids are the least desirable option due to the potential for severe side effects, but may be the only option for some cats. Inhalational corticosteroids (Figure 6) are an effective way to manage lower airway disease in cats (Padrid 2006), although they can take 1–2 weeks to become effective. An initial course of oral corticosteroids is appropriate, with a view to using inhaled medications once clinical signs are controlled. More information on inhaled therapy is included in Boxes 2 and 3

Bronchodilators may be useful in asthma cases with bronchoconstriction. Inhaled salbutamol (Box 2) can be useful in an acute episode at a dose of 100 μg (Reinero and DeClue, 2010). Other bronchodilators used in cats with lower airway disease include other beta2-receptor antagonists such as terbutaline, and methylxanthines such as propentofylline.

Other therapies include antibiotic therapy which should be based on culture and sensitivity results, although scant growth due to contamination is not unusual. Results should be interpreted with cytology findings and how heavy the growth is. Mycoplasma infection is treated with doxycycline or fluoroquinolones. Ciclosporin has been used successfully to treat a cat with asthma (Nafe and Leach, 2015), but further study is required before it can be recommended. Omega-3 polyunsaturated fatty acids and allergen specific immunotherapy (Reinero et al, 2006b) show promise and further publications are awaited.

Box. 2

Inhalational therapy for cats with lower airway disease

Inhalational therapy is provided via a metered dose inhaler (MDI) attached to a chamber and facemask. Inhaled corticosteroids and bronchodilators are used, although none are licensed for cats. Inhaled medications provide local drug distribution into the lungs, and are associated with fewer side effects than oral medication (Reinero et al, 2006a,b). Fluticasone is used widely as an inhaled corticosteroid at a starting dose of 125–250 μg twice daily and salbutamol is used as a bronchodilator at 100 μg every 30 minutes during an acute episode. Both are available from human pharmacies. Chronic use of salbutamol is not recommended as it may exacerbate airway inflammation (Reinero et al, 2009b).

Box. 3

Tips on introducing a facemask and spacer device

Owners may be initially anxious or apprehensive about using the spacer device. A consultation with a nurse to spend time answering questions and reassuring the client is valuable. Rushing the introduction to the spacer can result in reduced compliance.

The nurse should spend time with the client to discuss the benefits of this treatment and demonstrate how to use the equipment

Direct clients to reliable sources of information such as http://icatcare.org/advice/cathealth/using-inhaler-treat-feline-asthma-0 and www.breatheazy.co.uk

The sight, sound and smell of the spacer and inhaler can be alarming to a cat so they should be slowly habituated to the device at home

Before the owner uses the spacer and inhaler on the cat they should get the cat used to the facemask by applying it very briefly then giving a treat, (or playing with the cat if not food motivated) and very slowly leaving the mask on for longer periods

If the cat tolerates the mask, the spacer and inhaler can be attached and the process repeated until the cat tolerates having the whole apparatus held up to their face (without administering the medication)

The noise of the inhaler can be off putting for cats, it is like a hiss and the medication will smell unfamiliar. Owners should press the inhaler in the same room as the cat and reward with a treat or playing until the cat is not alarmed by the noise

Owners may lack confidence in their ability to give the medication and the cat's tolerance of the procedure. Support with nurse consults and follow up phone calls to encourage compliance.

Conclusions

Lower airway disease is common in cats and can be lifethreatening. Investigations include imaging and bronchoalveolar lavage. Management is based on the use of corticosteroids, but in inhaled form they are associated with fewer side effects. Bronchodilators, allergen avoidance and more recently therapies such as allergen specific immunotherapy may be other treatment options. The prognosis for cats with inflammatory lower airway disease is generally positive. Although life-long therapy is required, response to treatment is usually good. Deterioration or failure to respond should prompt reassessment of diagnosis, assessment of compliance, or a search for complicating factors such as infection. The veterinary nurse plays an important role in the care of affected cats, at initial presentation, during the investigation and crucially during treatment, when time spent with owners explaining and demonstrating the use of inhaled medication can make a great difference to compliance in the long term.

Key Points