WHAT IS CAT ASTHMA?
Asthma is a relatively common chronic inflammatory disease of the bronchial tubes in cats. It is a hypersensitivity reaction following sensitisation by an aeroallergen (allergen present in the air). The bronchi undergo variable pathological changes after repeated exposure to the same allergen: airway inflammation (white blood cells involved: eosinophils), mucus hypersecretion, intermittent and reversible bronchoconstriction (in response to allergic and non-allergic stimuli), and remodeling (permanent changes in lung architecture). History, clinical signs, radiological findings, and response to treatment are the key elements of diagnosis. Currently, there is no cure for this bronchial disease.
WHICH CATS CAN DEVELOP THE DISEASE?
The disease can affect cats of any age and breed. However, Siamese cats seem to be predisposed.
WHAT ARE THE CLINICAL SIGNS?
Owners often describe intermittent episodes of coughing, difficulty breathing, and abnormal breathing sounds (whistling, etc). It is not always easy to recognise a cough in cats. Some cats also present for vomiting, owners mistaking the coughing fit for retching. Similarly, a coughing fit can trigger vomiting, for which the animal is then presented at the end. Between coughing attacks and at rest, asthmatic cats often appear asymptomatic and the clinical examination may be completely normal. Other clinical signs that may be encountered at home are: rapid breathing, dyspnoea (especially expiratory), open mouth breathing. Others may be noted by the veterinarian during the clinical examination: Irritable cough on tracheal palpation, presence of fine crackles and whistles on auscultation.
WHAT OTHER DISEASES CAN CAUSE THE SAME CLINICAL SIGNS AS FELINE ASTHMA?
The most important other diseases to distinguish from feline asthma are chronic bronchitis, parasitic respiratory diseases (aelurostrongylosis, dirofilariosis, toxocariosis) and, less frequently, bacterial or tumorous respiratory diseases. The combination of different complementary examinations makes it possible to differentiate between these diseases.
SUPPLEMENTARY EXAMINATIONS THAT MAY BE CONSIDERED TO DETERMINE DIAGNOSIS
There are no specific changes in the blood count for feline asthma. Cats that have spent time in a heartworm endemic area should be serologically tested for the disease, which can cause the same clinical signs as feline asthma.
Faecal analysis (Baermann technique) can detect Aelurostrongylus sp. infection if the parasite is present in the faeces, but a negative analysis does not rule it out.
Chest radiographs allow the exclusion of certain lesions (tumor, focal infection, mediastinal mass, pleural effusion) and, if present, demonstrate the signs commonly observed in asthma (diffuse bronchial and/or peribronchial lung drawing, more or less pronounced). Other, less common signs may be observed (flattened diaphragm, etc.). X-ray examination may appear completely normal, which does not rule out the presence of the disease. Some diseases, such as chronic bronchitis, may show the same changes on the X-ray.
Another diagnostic imaging technique, the CT scan, is more effective than the conventional X-ray in differentiating certain respiratory diseases, but requires: an office equipped with a scanner, often a general anesthetic, and is associated with additional costs. This technique is therefore not always used in the diagnosis of asthma.
In practice, clinical, blood, X-ray, and possibly stool tests help to confirm the clinical suspicion of feline asthma. Treatment is often initiated at this stage. The response to corticosteroids can be considered a diagnostic test. It must be excellent (see Treatment). Initially, corticosteroid treatment is often accompanied by antiparasitic and antibiotic treatment.
Bronchoscopy, bronchoalveolar lavage (BAL) and cytological examination
A bronchoscopic examination is considered immediately or when there is an unsatisfactory response to therapy. It aims to exclude other causes of cough and/or breathing difficulties (bacterial infection, parasitosis, …) and to detect common abnormalities in allergic bronchitis if any: Hypersecretion of mucus, irregularity of the mucosa, eosinophilic inflammation on cytological examination of the BAL fluid.
Certain other tests (identification of the allergen, plethysmography) are generally performed in research centers (and are therefore less accessible) and are only considered in specific cases.
TREATMENT OF FELIN ASTHMA
A cure is not generally possible at present, as in humans. It is only possible if the allergen in question is identified and eliminated, which is usually utopian. Chronic drug treatment and regular monitoring are necessary to reduce symptoms and counteract bronchial remodeling. Treatment recommendations include environmental modifications, corticosteroids, and bronchodilators (in case of an acute attack).
In practice, exposure to irritants such as powder, dusty litter, aerosols or cigarette smoke should be avoided. For cats living in flats, room air filters may help.
For long-term treatment, glucocorticoids are recommended to break the inflammatory cycle that causes irreversible bronchial damage. They can be administered orally, by injection, or by inhalation. The dosage should be adjusted according to the clinical response to treatment, with the aim of adjusting the cat to the lowest therapeutically effective dose in the long term after a gradual dose reduction. Inhaled corticosteroids are well tolerated when administered chronically but are not effective in emergency treatment. They reduce inflammation and induce fewer systemic side effects than the oral form. They are administered through a chamber fitted with a mask. The Aerokat® device is specifically designed for cats. The administration of long-acting injectable corticosteroids should be reserved for cases where oral administration is not possible. It is important to remember that the clinical efficacy of systemically administered corticosteroids must be excellent. If this is not the case, another cause for the cough must be sought.
Bronchodilators are indicated in cats with attacks of bronchoconstriction. Their use is not recommended as monotherapy as they do not act on inflammation. They are usually administered orally or by injection, or inhaled in certain cases. Some bronchodilators may paradoxically worsen bronchial inflammation. Their use is therefore reserved for the short-term treatment of an asthma attack.
The use of ciclosporin may be considered in certain special cases (contraindicated corticosteroids, etc.). Its use has been documented in some experimental models and in some case reports.
Antibiotics are mainly indicated in cases where bacterial superinfection is suspected (e.g. in case of inadequate response to corticoids) or diagnosed by culture of BAL fluid. The presence of bacteria in the BAL does not always indicate infection, as some healthy cats may have large numbers of bacteria. Identification of bacteria should always be interpreted in conjunction with the results of the cytological analysis. If a culture is performed, the choice of antibiotic will be targeted. If this is not the case, empirical antibiotic therapy can be used. Immunotherapy is a very promising avenue of research. “Rush immunotherapy” consists of stimulating the immune system to tolerate the allergen by exposing it to the causative agent. This treatment is potentially curative. In cats, studies have shown a reduction in the inflammatory response with or without improvement in clinical signs. Further work on immunotherapy and other potential new treatments is ongoing.
Cats with feline asthma can have an excellent quality of life, but it is very important to make the correct diagnosis and monitor these patients regularly, as they usually require long-term treatment.