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Show all small animal articles

Feline Asthma – part 2

Germán Santamarina Pernas, DVM, PhD - 03/06/2015

Feline Asthma – part 2
Germán Santamarina Pernas, DVM, PhD

Clinical presentation

The incidence of feline asthma is probably underestimated but it is thought to affect 1% of the population. It is the most frequent cause of coughing in cats. Although it affects cats of any age, it is more common in young and middle-aged cats. The Siamese breed may be over-represented with a prevalence that can be up to 5%. This suggests that there is a genetic predisposition similar to the human situation (1,8).

Clinical signs may be quite different according to the degree of affliction. The most frequent signs are coughing, wheezing, and respiratory harshness, which can vary from day to day. In mild cases, clinical signs are limited to short and occasional coughing bouts. These signs tend to be chronic or to progress slowly. Some cats with asthma may remain asymptomatic between occasional episodes of acute airway obstruction. In severe cases, cats can develop a daily persistent cough with frequent acute dyspnoeic crises.

Aggravation or induction of clinical signs may occur associated with exposure to potential allergens or irritant agents such as a new bed, cigarette or chimney smoke, cleaning products or perfumed air fresheners, dust or seasonal pollen. Clinical signs tend to worsen with stress or exercise. Weight loss can be evident in cats that have chronic respiratory disease. However, those cats which restrict their activity due to respiratory disease may become overweight (1,3,6,8).

During the dyspnoeic crises, cats tend to adopt a typical position; lying on the floor in sternal recumbence, their head and neck extended, the mouth opened and with wheezing respiration. If bronchoconstriction lasts long enough, the cat can become cyanotic and the thorax can adopt a barrel shape due to air trapped inside. Dyspnoea intensity may be assessed by the degree of the lateral retraction of nostrils and the corners of the mouth (8).

Diagnostic tests

Physical examination... many asthmatic cats may have a normal physical exam at rest. However, in cases where the cat is severely affected due to the blockage of the lower respiratory tract, a significant expiratory distress will be typically noticed with adventitious sounds such as crackling. Wheezing can be detected when the disease is advanced or during acute aggravation episodes. Blocked airways may have air trapped distally which reduces thoracic compressibility; as noted above this may cause the thorax to become barrel-shaped (1,3,6,8).

Blood tests... approximately only 20% of cats with feline asthma have peripheral eosinophilia. This is not a very specific finding because there are other conditions that can demonstrate this (e.g. lung parasites, gastrointestinal parasites, heart worms, ectoparasites…) (3,6). Cats with asthma may show a stress leukogram, but this is also not specific. Blood chemistry seldom provides relevant information regarding lung disease, yet there are certain tests that can help eliminate some potential conditions from the differential diagnosis. It is worth considering a serum test for Toxoplasma gondii, and in areas where Dirofilaria immitis is endemic, it is recommended to perform serum tests for detection of antigen and heart worm antibody in cats with respiratory signs (3,4).

Faecal exam... Aelurostrongylus abstrusus, Paragonimus kellicotti or Capillaria aerophila infections can cause coughing and respiratory harshness in cats. In endemic areas, these lung parasites should be excluded by proper faecal testing, including flotation with or without centrifugation techniques (to detect Paragonimus and Capillaria eggs) and Baermann sedimentation (to detect larvae of Aelurostrongylus) (1,3,4).

Thoracic X-Ray... the classic radiographic pattern of a cat with asthma tends to show swelling of the bronchial walls, figure 4 - lateral and ventrodorsal thoracic radiographs of a cat with asthmagenerally described as “doughnuts” and “railway lines” (Figure 4). In addition there may be evidence of increased radiolucency of the lungs and flattening and caudal displacement of the diaphragm, recognized when observing the diaphragmatic pillars around the lumbar vertebrae area L1-L2. Around 15% of asthmatic cats display an increased density of the right middle lung lobe and a central displacement towards the right. This sign is related to the presence of atelectasis in the lung lobe as a result of accumulation of mucus in the bronchi. Even though atelectasis may affect several lobes, it is particularly common in the right middle lobe, as its bronchus is oriented ventrally from the bottom of the main right bronchial tube; this means that mucus tends to build up due to gravity (3,8).

It is important to highlight that some cats with asthma may present a normal radiograph; therefore a diagnosis of asthma cannot be disregarded based only on the absence of radiographic signs.

Therapeutic trial... when a cat has respiratory symptoms that are thought to indicate asthma, a therapeutic trial can be carried out by the administration of bronchodilators. Coughing and wheezing in cats with asthma normally disappear 10 minutes after administering bronchodilators (terbutaline 0.01 mg/kg, IV, IM or SC; albuterol 100 ìg inhaled (Figure 5)). figure 5 - inhaled therapy with a measured dose inhaler (MDI) attached to a spacing chamber and connected to a facial maskMost asthmatic cats respond to treatment in 5-7 days with a high-dose corticosteroid therapy and, if no evident improvement is shown, the diagnosis for feline asthma should be reviewed (1,3).

Bronchoscopy... bronchoscopy is not a procedure frequently undertaken when investigating a possible case of feline asthma. In cats with coughing and respiratory compromise, bronchoscopy involves certain risks and will rarely be necessary to determine a definite diagnosis of asthma in a patient. Nevertheless, on a few occasions it might be useful to eliminate other pathologies from the differential diagnosis. The bronchoscopy in feline asthma typically reveals erythma and mucous edema, reduction of airway luminal calibre and (sometimes) evidence of excessive mucous and mucous plugs (1,3,9,10).

Endotracheal/bronchoalveolar wash procedures... cytological findings obtained during endotracheal and/or bronchoalveolar wash procedures are not pathognomonic of feline asthma. Generally in cats suffering from asthma, evidence of airway inflammation is noted with an increase in the number of eosinophils recovered from bronchial secretions. However, several studies have made it clear that an eosinophilic preponderance (20-25% of total cell count) recovered from tracheobronchial wash procedures may be found in many normal cats. Thus eosinophilia in bronchial samples must not be taken into account when seeking a definitive diagnosis of feline asthma (1,3,9,10).

Once aseptic samples are obtained from an endotracheal or bronchoalveolar wash, cultures and antimicrobial sensitivity tests may be performed to check for aerobic bacteria and Mycoplasma spp.

However, it is worth noting that some organisms normally considered as pathogenic, such as Klebsiella or Pseudomonas spp., can be found in samples obtained from healthy cats. In fact, the bacteria isolated from an asthmatic cat’s airways will most likely reflect colonization rather than infection. The finding of Mycoplasma may be an exception, as these microorganisms have been isolated only from the airways of cats with respiratory disease, not from healthy cats. The role of Mycoplasma in feline respiratory disease is not yet known, but it has been noted that this organism can contribute to the degradation of neutral endopeptidase, the enzyme responsible for the destruction of substance P, a protein capable of causing bronchoconstriction and oedema in feline airways. Mycoplasma – along with certain viruses which can remain dormant in the cat’s airways for long periods – is thought to be the responsible agent for the increase in substance P levels contributing to spontaneous bronchoconstriction in asthmatic cats. It is important to bear in mind that isolation of Mycoplasma is difficult and requires specialised growth mediums, so handling and submission of laboratory samples must be done correctly (1,9).

Lung function tests... typically used in human medicine to check for pulmonary disease, are difficult to implement in veterinary practice due to the limited cooperation by animals. However, some methods have been developed to assess pulmonary function in cats, yet are rarely implemented in veterinary practice and are currently restricted to teaching and research institutions. Measurement of respiratory tidal volume-flow curves have confirmed that cats with bronchial disease have an increased ratio in the expiration time: inspiration time, a reduction in the area below the expiration curve, lower rates of expiratory flow, lower expiratory tidal volumes and increased median pulmonary resilience. These changes in resilience during the expiratory phase are compatible with an obstructive disease of the lower respiratory tract. Full-body plethysmography is another technique being researched for evaluation of lung mechanisms and has proved useful to assess a normal cat’s airway reactivity. The application of this technique in cats with asthma would allow confirmation of airway hypersensitivity and permit the clinician to measure the response to bronchodilators in asthmatic cats (3).

Treatment

Table 2Not every asthmatic cat develops the disease to the same degree, therefore disease management may vary depending on the severity of the condition (11,12). On the other hand, respiratory crises are feasible in any asthmatic cat, and the control of a patient with an acute dyspnoeic crisis will differ from the treatment of a cat that is not undergoing a crisis (Table 3).

Table 3

Therapeutic strategies for the treatment of asthma are generally focused towards the suppression of inflammation and the reversal of bronchoconstriction (Table 4). The trend among new therapies is towards attempts to eliminate the exaggerated hypersensitivity reaction before it can trigger inflammation and bronchoconstriction of airways.

 

Table 4

Treatment for an acute crisis

Cats that are presented in acute crisis with severe respiratory distress must be handled with care, minimizing stress and delaying, where necessary, diagnostic testing. In these situations, it is important to administer oxygen by placing the cat inside an oxygenation cage with a FiO2 of at least 40%. This is normally an efficient and low-stress method to administer oxygen to a cat suffering from asthma (Figure 6). Initially, the cat will be administered bronchodilators to neutralize the acute bronchoconstriction. First choice bronchodilators for these emergency situations are the β2-adrenergic antagonists (terbutaline and albuterol). These drugs quickly and selectively stimulate β receptors, and produce almost immediate relaxation of smooth muscle in the airways. If there is no favourable response to the initial dose within 15 - 30 minutes the bronchodilator should be repeated along with a short-term corticosteroid such as dexamethasone. Once the patient has been stabilized it is necessary to continue with the diagnostic evaluation to achieve satisfactory long-term treatment.

Figure 6 - A cat with asthma

Conclusion

Feline asthma is a condition that any small animal clinician must be able to recognize and treat successfully, although the mechanisms of this disease are not fully understood. There is no single definitive diagnostic test available and it may be necessary to employ a variety of tests, and to eliminate other possible diseases that cause respiratory signs, to reach a tentative diagnosis. Treatment should be geared towards the individual animal and must be based on an accurate appraisal of the animal’s needs.

 

 

This article was kindly provided by Royal Canin, makers of a range of veterinary diets for dogs and cats.  For the full range please visit www.RoyalCanin.co.uk or speak to your Veterinary Business Manager:

References

1. Padrid P. Asthma. In: August JR (ed). Consultations in feline internal medicine. Philadelphia: WB Saunders 2010; 447-458.

2. Hill JW. In: Jenkins WR (ed): The diseases of the cats. Diseases of the respiratory organs.. New York 1906; 11-22.

3. Bay JD, Johnson LR. Feline bronchial disease/asthma. In: King LG (ed). Textbook of respiratory disease in dogs and cats. Philadelphia: WB Saunders 2004; 388-396.

4. Byers ChG, Dhupa N. Feline bronchial asthma: pathophysiology and diagnosis. Compend Contin Educ Vet 2005; 27: 418-425.

5. Norris Reinero CR, Decile KC, Berghaus RD, et al. An experimental model of allergic asthma in cats sensitized to house dust mite or bermuda grass allergen. Int Arch Allergy Immunol 2004; 135:117-131.

6. Cohn LA. How to help the asthmatic cat breathe easy. Proceedings of the North American Veterinary Conference. Orlando, Florida 2007; 1267-1269.

7. Dye JA, McKiernan BC, Rozanski EA, et al. Bronchopulmonary disease in the cat: historical, physical, radiographic, clinicopathologic, and pulmonary functional evaluation of 24 affected and 15 healthy cats. J Vet Intern Med. 1996; 10: 385-400.

8. Thébault A. Affections respiratoires chez le chat: diagnostic et traitement de l’asthme du chat. Point Vét 2004; 248: 26-30.

9. Foster SF, Martin P, Braddock JA, et al. A retrospective analysis of feline bronchoalveolar lavage cytology and microbiology (1995-2000). J Feline Med Surg 2004; 6:189-198

10. Johnson LR, Drazenovich TL. Flexible bronchoscopy and bronchoalveolar lavage in 68 cats (2001-2006). J Vet Intern Med 2007; 21: 219-25.

11. Byers ChG, Dhupa N. Feline bronchial asthma: treatment. Compend Contin Educ Vet 2005; 27: 426-431.

12. Padrid PA. Use of inhaled medications to treat respiratory diseases in dogs and cats. J Am Anim Hosp Assoc 2006; 42:165-169.

13. Cohn LA. Inhalant therapy: finding its place in small-animal practice. Vet Med 2009; 336-341.

14. Cohn LA, DeClue AE, Reinero CR. Endocrine and immunologic effects of inhaled fluticasone propionate in healthy dogs. J Vet Intern Med 2008; 22: 37-43.

15. Powell LL. Inhalation therapy. Proceedings of the North American Veterinary Conference. Orlando, Florida 2007; 220-221.

16. Reinero CR, Delgado C, Spinka C, et al. Enantiomer-specific effects of albuterol on airway inflammation in healthy and asthmatic cats. Int Arch Allergy Immunol 2009; 150: 43-50.

17. Padrid PA, Mitchell RW, Ndukwu IM, et al. Cyproheptadine-induced attenuation of type-I immediate-hypersensitivity reactions of airway smooth muscle from immune-sensitized cats. Am J Vet Res 1995; 56: 109-115.

18. Padrid PA, Cozzi P, Leff AR. Cyclosporine A inhibits airway reactivity and remodeling after chronic antigen challenge in cats. Am J Respir Crit Care Med 1996; 154: 1812-1818.

18. Padrid PA, Cozzi P, Leff AR. Cyclosporine A inhibits airway reactivity and remodeling after chronic antigen challenge in cats. Am J Respir Crit Care Med 1996; 154: 1812-1818.

 

This article was previously published in 2011.

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