013 Feline Asthma: 10 Bits of Jibber Jabber

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***Dyspnoeic cats very vulnerable. Risk-benefit analysis absolutely essential throughout.***
 

1. What do we call this syndrome?

‘Feline asthma’ most widely used term; may be some differences however from asthma in people
Other terms that have been used to describe inflammation of the lower airways in cats without an identifiable cause include feline bronchial disease, feline lower airway disease, and feline allergic airway disease.

2. Pathogenesis:

Complex and multifactorial but allergens or non-specific airway irritants likely to be involved in initiating or at least exacerbating airway inflammation
Relationship between respiratory infection and feline bronchial disease remains to be clarified
Allergens/irritants thought to trigger airway Type I hypersensitivity reaction which results in:

  • Bronchial inflammation
  • Mucosal oedema
  • Bronchoconstriction
  • Mucus gland hypertrophy and excessive mucus secretion
  • Airway hyper-reactivity

Net result is LOWER AIRWAY OBSTRUCTION.

Signs may be acute and episodic but reversible, while in others chronic inflammation results in irreversible fibrosis and emphysema.
Eosinophils likely primarily involved in inflammatory response but eosinophilic airway inflammation not specific to asthma

Hallmark features:

  • Airway inflammation
  • Airway hyper-reactivity or hyperresponsiveness
  • Limitation of airflow
  • Potential airway remodelling

3. Who gets feline asthma?

Basically any cat
Clinically most prevalent in young- to middle-age cats – some cats may have chronic subclinical pathology for some time before clinical episode
Siamese cats may be over-represented
Prevalence of chronic subclinical asthma unknown

4. Clinical findings:

Spectrum with respect to both severity and frequency
Chronic, intermittent cough through to acute, episodic respiratory distress
Acute clinical signs most commonly include coughing, and variable degrees of tachypnoea or dyspnoea; latter can be very severe, potentially life-threatening.
Lung auscultation may reveal harsh lung sounds potentially with wheezes on expiration and sometimes crackles.
‘Expiratory push’ may be present but not always.
Should not exclude asthma just because wheezing or expiratory push is absent

Airway rupture due to asthma will result in spontaneous pneumothorax – dull lung sounds dorsally or diffusely if severe.

Some reports of asthmatic cats presenting with episode of vomiting during an episode of paroxysmal coughing or hacking rather than respiratory distress. 

5. Diagnosis:

Presumptive emergency diagnosis typically on basis of consistent clinical findings, exclusion of other differential diagnoses that could lead to an acute dyspnoeic episode, and especially positive response to appropriate therapy.

More definitive diagnosis only after adequate stabilisation
No one gold standard test. Diagnosis on the basis of supportive data collected from thoracic radiography, bronchoscopy and bronchoalveolar lavage (BAL) analysis, both cytology and culture. Exclude other causes of lower airway disease.

6. Thoracic radiography:

***Only at appropriate time. Think risk-benefit analysis at all times.***

Abnormalities may include a bronchial, interstitial, alveolar or mixed lung pattern
Severe diffuse bronchointerstitial lung pattern may be identified with some frequency
Severe lower airway obstruction may result in air trapping and lung hyperinflation; identified radiographically as increased pulmonary radiolucency and flattened caudally-displaced diaphragm.

7. Treatment – Acute crisis:

Standard principles for initial approach to dyspnoeic cats: liberal oxygen supplementation, ‘hands off’ minimally invasive handling, thinking very carefully about risk-benefit analysis etc.
Urgent medical therapy

Current therapy directed towards:

  • Suppressing airway inflammation
  • Bronchodilation

Parenteral glucocorticoids mainstay of acute life-saving therapy
Adjunctive parenteral bronchodilator – DO NOT use as sole therapy in an acute case:

  • β2-adrenergic receptor agonist, e.g. terbutaline
  • Methylxanthines, e.g. aminophylline

8. Treatment – Subacute and Chronic:

Time to inclusion of additional topic therapies and transitioning to oral therapies depends on individual cat’s progress and level of tolerance for topical/oral therapies
Oral prednisolone: dose and the duration of therapy depends on individual cat’s response and whether topical therapy is also being used
If inhaled glucocorticoids are also being used and the patient is doing well with good compliance, prednisolone can be tapered and discontinued more quickly.

Topical glucocorticoids (e.g. fluticasone):
Should not be used alone in an acute crisis; may be used additionally if patient is tolerant.
Going forward they offer an attractive alternative with a significantly lower risk of side-effects compared with systemic glucocorticoids
But can be expensive and not all cats are tolerant; patient compliance can be improved by gradual introduction with period of sensitisation to topical administration.

Fluticasone:
Administered by metered dose inhaler attached to spacer device and face mask (e.g. AeroKat® Feline Aerosol Chamber)
Thought to have low systemic bioavailability following inhalation so generally not associated with adverse effects seen with long-term prednisolone use
Unclear but may take up to 2 weeks to reach maximum efficacy

Topical bronchodilator – e.g. inhaled albuterol:
Short-acting β2-agonist
Some data suggesting should not be used on daily basis; may be better kept as a potential rescue therapy

Chronic therapy protocol depends on individual cat – severity of disease, compliance with topical therapy – and carer’s preferences, abilities, compliance etc.

9. Alternative or novel therapies?

Some combination of glucocorticoids and bronchodilators is usually effective in managing most asthmatic cats and glucocorticoids at any rate are pretty cheap.
Why might alternative or novel therapies be attractive? Reasons include:

  • Cats that cannot be well controlled with the standard approach
  • Cats in which chronic glucocorticoids have unacceptable adverse effects
  • Cats in which glucocorticoids are absolutely or at least relatively contraindicated from early on (e.g. diabetic)

And… current therapies may control the syndrome adequately but they may not necessarily be directly addressing the cause of the problem, i.e. hypersensitivity immune system dysfunction.
Directly tackling immune dysfunction may prevent chronic structural lung changes (remodelling, irreversible fibrosis) and potential long-term lung dysfunction.

Allergen-specific immunotherapy:
Carers of asthmatic cats should be questioned at length and advised extensively about possible allergens (e.g. cat litter, cigarette smoke, carpet cleaners, air fresheners) in the home and importance of minimising the cat’s exposure to them.
BUT If specific inciting allergens can be identified by testing then allergen specific-immunotherapy may be possible and may become increasingly available in the clinical setting.

Lots of experimental therapies: none yet to actually undergo proper process of evaluation in clinical cats with naturally-occurring disease.

10. Cyclosporine:

Recent case report (Nafe, Leach, 2014 – see below) in which this was used to treat a cat with asthma.

Abstract: “A 5-year-old domestic shorthair cat that had been previously diagnosed with diabetes mellitus was presented for episodes of coughing and respiratory distress. Diagnostic testing revealed congestive heart failure secondary to hypertrophic cardiomyopathy and concurrent asthma. All clinical signs and eosinophilic airway inflammation resolved with oral ciclosporin while concurrently receiving medications for treatment of heart failure (furosemide and enalapril). Ciclosporin should be considered for treatment of feline asthma in patients with concurrent diseases  (eg, diabetes mellitus, severe heart disease) that may contraindicate use of oral glucocorticoid therapy.”

At the time the cyclosporine was used in this cat patient would be classified as chronic with variable clinical signs; NOT used as part of stabilising an acute crisis
Treated with cyclosporine for 3 weeks
Evidence for beneficial effect:
Improvement in cough and tachypnoea at home
Improvement in inflammatory cytology from consecutive blind BAL samples

Cyclosporine was tapered off while inhaled fluticasone was introduced; then maintainedon this. Done to minimse costs and potential adverse effects of long-term cyclosporine use.

Cyclosporine relatively well known as an immunomodulatory agent. Typically used as adjunctive or second-line agent in immune-mediated disorders; also e.g. in allergic dermatitis. Can be considered as sole agent in glucocorticoid-intolerant cases.
Appears to be relatively well tolerated in cats

Having said that the evidence base for cyclosporine use in cats in general is still relatively scant and much more is needed. With respect to use in asthma, need to bear in mind this is just a single case report of a cat with a specific set of circumstances.


Some papers that informed this episode:

Cooper ES, Syring RS, King LG. Pneumothorax in cats with a clinical diagnosis of feline asthma: 5 cases (1999-2000). J Vet Emerg Crit Care 2003. 13(2):95–101.

Liu DT, Silverstein DC. Feline secondary spontaneous pneumothorax: A retrospective study of 16 cases (2000–2012). J Vet Emerg Crit Care 2014. 24(3):316–325.

Nafe LA, Leach SB. Treatment of feline asthma with ciclosporin in a cat with diabetes mellitus and congestive heart failure. J Fel Med Surg 2014. Online. Accepted 6 November 2014.

Reinero CR. Advances in the understanding of pathogenesis, and diagnostics and therapeutics for feline allergic asthma. Vet J 2011. 190(1):28-33.

Trzil JE, Reinero CR. Update on Feline Asthma. Vet Clin Sm Anim 2014. 44:91-105.

Venema C, Patterson C. Feline asthma: What’s new and where might clinical practice be heading? J Fel Med Surg 2010. 12:681-692. 

Whitehouse W, Viviano K. Update in Feline Therapeutics: Clinical use of 10 emerging therapies. J Fel Med Surg 2015. 17:220–234.

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