Read the French translation: Bronchite Féline: Où en Sommes-Nous?
Introduction
In cats, coughing is an infrequent clinical sign while it is frequently encountered in dogs. Besides, in cats, coughing is fairly specific for tracheobronchial disease since cough of cardiac origin is rare. Feline bronchial disease (feline asthma or bronchitis) is characterized by inflammation of the lower airways without an obvious identifiable cause. Many other terms are found in the literature (such as chronic bronchitis, allergic bronchitis, eosinophilic bronchitis, bronchial asthma). However, presently, it is not clear whether an allergic form can be differentiated from a chronic disease of other origin. Feline bronchitis is recognized clinically by various combinations of coughing, wheezing, exercise intolerance, and respiratory distress attributable to airway obstruction caused by bronchial inflammation.
Clinical Signs
Young to middle-aged cats are most commonly affected. Clinical signs are often chronic or slowly progressive and are related to reversible airway inflammation and subsequent obstruction. Airway obstruction is linked to hyperreactivity and smooth muscles hypertrophy, excessive production and accumulation of mucus (mucous gland hypertrophy), and bronchial wall oedema. Those changes are sometimes reversible. However, chronic inflammation can lead to severe lower airway obstruction which causes lung hyperinflation: affected cats are unable to exhale completely through the narrowed airways, resulting in air trapping. Lung hyperinflation may lead to permanent pathology, evidenced by progressive bronchiectasis, fibrosis or emphysema. Mildly affected cases may only have occasional and brief episodes of cough separated by long periods without symptoms. However, cats with severe exacerbations may present acutely with open mouth breathing, dyspnoea and cyanosis. Exacerbation may occur in association with exposure to potential allergens or irritants, or after stress or exercise.
Diagnosis
Physical examination can be normal at rest, cats may exhibit a prolonged expiratory phase and wheezes or crackles may be heard. Routine thoracic radiographs can be within normal limits in some cats. The classic pattern includes evidence of bronchial wall thickening (doughnuts or railroad tracks); air trapping may also be evident (increased lucency and flattening of the diaphragm); as well as sometimes right middle lung lobe atelectasis.
Approximately 20% of the cats have a peripheral eosinophilia, a stress leukogram can be observed, as well as secondary polycythemia or hyperglobulinemia. Fecal examination is recommended as part of the diagnostic work-up (Aelurostrongylus, Capillaria).
Cytological examination of airway samples, obtained by bronchoalveolar lavage (BAL) or endotracheal wash (ETW) generally provides evidence of airway inflammation, with increased numbers of eosinophils and/or neutrophils. Although a preponderance of eosinophils may be found in fluids from healthy cats, the number of eosinophils and neutrophils in BAL fluid has been shown to correlate with the disease severity, both in cats with spontaneous disease and with experimentally-induced bronchial disease.
Samples of BAL and ETW fluid may be submitted for culture of bacterial and mycoplasmal organisms, although the significance of a positive culture should be interpreted with caution.
Pulmonary function testing is commonly used in human medicine, in the diagnosis and monitoring of therapeutic response in patients with asthma or chronic bronchitis. In cats, some non invasive tests have been developed, such as tidal breathing flow volume loop, and whole body barometric plethysmography.
Differential Diagnosis
Includes mainly parenchymal diseases, such as infectious pneumonia/bronchopneumonia (bacterial, viral, parasitic, protozoal), rare but probably under-diagnosed, airway foreign bodies, neoplasia, pleural effusion, and rarer diseases such as "feline pulmonary fibrosis" and "endogenous lipidic pneumonia".
Treatment
In cats with severe acute respiratory distress, stress should be minimized and an oxygen enriched environment should be provided. Parenteral therapy with bronchodilators (β2 agonists, for instance terbutaline 0.01 mg /kg IV, IM or SC) or rapidly acting corticosteroid (e.g., dexamethasone 0.25 to 2 mg / kg IV or IM) should be administered. Inhaled bronchodilator medication can be used as well.
Classic therapy of chronic forms of bronchial disease includes decreased exposure to potential allergen/irritants and the use of long term, oral corticosteroid, (oral prednisone or prednisolone, 1 to 2 mg / kg BID for 1 to 2 weeks, followed by gradual taper of the dose) which remains the most consistent, reliable and effective treatment to date.
New therapeutic strategies, based on the use of immunomodulatory substances, like cyproheptadine, cyclosporine, leukotriene modifiers and antiinterleukin-5 antibody, have been tested in experimental settings, but until clinical trial reports are published, their use cannot be recommended. The use of inhaled medication seems more promising. Medications given via inhalation offer the advantage of high drug concentrations within the airways while attenuating systemic side effects. Inhaled corticosteroids (e.g., fluticasone propionate), utilized essentially as chronic therapy, and bronchodilators (e.g., albuterol), used to palliate an acute exacerbation of symptoms, are the most commonly used.
There is lack of clinical trials comparing different treatment modalities in bronchial diseases in cats. Moreover, the use of non invasive function tests associated with bronchoprovocative testing would be needed routinely and would provide an objective evaluation of both initial disease severity and response to therapy.
References
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