Feline asthma has been referred to in the literature by a variety of terms including eosinophilic bronchitis, allergic bronchitis, feline bronchitis, feline bronchial asthma, and feline chronic obstructive pulmonary disease.^1,2 Cats of all ages may be affected.³ There is an increased incidence in Siamese cats, and they may have a more chronic form of bronchial disease.⁴

PATHOLOGY

Histopathological lesions of feline asthma include: bronchial smooth muscle hypertrophy and bronchoconstriction; inflammation and edema of airway mucosa and submucosa; epithelial cell desquamation, intraluminal inflammatory exudate, and airway mucus plugs; and emphysema, submucosal gland hyperplasia, and increased airway goblet cells.¹

CLINICAL SIGNS

Clinical signs may be mild and chronic or acute and severe with cough and/or dyspnea and may be exacerbated by environmental changes.⁵ The cat may have a history of a recent upper respiratory tract infection and sneezing or oculonasal discharge may be present.^5,6 On physical examination the cat may appear normal at rest but exhibit increased tracheal sensitivity with auscultable post-tussive crackles.⁵ A more severely affected cat may have harsh lung sounds, crackles, or wheezes on expiration with a prolonged expiratory phase or decreased lung sounds with a barrel-shaped thorax and increased resonance on percussion.^1,5 An abdominal component to respiration may be present.⁵ A severely affected cat may present with extreme respiratory distress, cyanosis, and open-mouth breathing.⁵

DIAGNOSIS

Differential diagnoses for cough and/or dyspnea in the cat include: (1) feline asthma; (2) pulmonary infection (bacterial, fungal, parasitic, viral, protozoan); (3) pleural effusion (chylothorax, pyothorax, hydrothorax, hemothorax); (4) pneumothorax; (4) pulmonary thromboembolism; (5) cardiac failure; (6) upper airway obstruction (nasal, laryngeal, tracheal); (7) bronchial foreign body; (8) neoplasia (upper airway, lower airway); and (9) heartworm disease.^1,7 Diagnostics should include: (1) complete blood count; (2) fecal examination; (3) thoracic radiographs; (4) heartworm test; (5) biochemical profile; (6) urinalysis; (7) feline leukemia virus and feline immunodeficiency virus test; (8) airway sampling; and (9) pulmonary function testing if available.¹ A complete blood count may reveal neutrophilia, eosinophilia, and hyperproteinemia.³ Thoracic radiography may be normal or abnormalities may be present including: peribronchial cuffing; alveolar or interstitial infiltrates; flattening of the diaphragm; air trapping or hyperlucency; and atelectasis of the right middle lung lobe.⁵ Cytology of airway samples reveals inflammation.³ Bacterial culture of airway samples is positive in 24-42% of cats but may only represent bacterial colonization and not actual infection.^3,4 Isolation of Mycoplasma may be an exception, though, as it is not normally isolated from the lungs of normal cats.^8,9 Pulmonary function testing may reveal increased airway resistance, airway hyperreactivity, and abnormalities in tidal breathing flow-volume loops.^3,10

PATHOGENESIS

In an attempt to better understand the pathogenesis of feline asthma, studies have been performed in a feline model induced by antigen sensitization and challenge with Ascaris suum.¹¹ In this model cats develop airway hyperreactivity and histopathological changes comparable to cats and humans with naturally-occurring disease.¹¹ A role for products of activated T cells in this model has been suggested based on experiments in which treatment in antigen-sensitized and chronically challenged cats with cyclosporine A (inhibitor of T cell activation and cytokine synthesis) inhibited the development of eosinophilic airway inflammation, airway remodeling, and airway hyperreactivity.¹² Additional studies in this model in vitro have shown that serotonin is a primary mediator in feline mast cells which contributes to airway smooth muscle contraction.¹³

THERAPY

Inhalation Therapy

There are several inhaled drugs designed for the treatment of human asthma that have been used in cats with feline asthma.^2,14 To administer a drug by inhalation to a cat, a metered dose inhaler is attached to a spacer, designed for young children (Aerochamber from Invacare), that is attached to a face mask made specifically for cats.^2,14 The metered dose inhaler is actuated once or twice, and the mask is held over the cat's face.^2,14 The cat is allowed to take 7-12 breathes before the mask is removed.^2,14

Corticosteroids

Corticosteroids are potent anti-inflammatory drugs and the mainstay for treatment of feline asthma.^2,14 Ideally to minimize the risk of systemic side effects, corticosteroids should be administered by inhalation. Most experience has been gained using fluticasone (2 puffs or 220 µg BID).^2,14 Moderately affected cats may need to be treated initially with a systemic steroid as well (1 mg/kg prednisone PO BID for 5 days, followed by 1 mg/kg prednisone PO once daily in the PM for 5 days).^2,14 Severely affected cats should be treated with dexamethasone initially (2 mg/kg IV).²

Bronchodilators

Bronchodilators may be necessary in addition to corticosteroids, especially initially, for control of clinical signs. Albuterol, a short-acting β₂-agonist with a rapid onset of action can be administered every 30 minutes (one puff or 90 µg) up to 8 times daily.^2,14 Ipratropium bromide, an anticholinergic agent, may be useful if clinical signs are not controlled adequately with β₂-agonists alone.^2,14

Cromolyn Sodium and Nedocromil Sodium

These drugs are chloride channel blockers that modulate mast cell mediator release and eosinophil recruitment.^2,14 Because of the evidence supporting a role for serotonin release from mast cells in bronchoconstriction in feline asthma, these drugs are potentially beneficial.^2,14

Cyproheptadine

Cyproheptadine (2 mg/kg PO every 12-24 hours) may be a useful addition to the treatment regimen in a cat with asthma that is not adequately controlled with steroids and bronchodilators.^2,14 Increased appetite and depression are common side effects.^2,14

Cyclosporine

Cyclosporine may be helpful as a last resort in the cat with severe asthma that is not controlled with high-dose corticosteroid therapy.^2,15

Antibiotics

Antibiotic therapy is indicated only if tracheobronchial sample cultures are suggestive of a pathogenic bacterial infection or positive for Mycoplasma spp.^2,14 Doxycycline, azithromycin, or fluoroquinolones are rational choices for treatment of Mycoplasma spp.¹⁴

References

1.  Dye JA. Feline bronchopulmonary disease. Vet Clin North Am Small Anim Pract 1992; 22(5): 1187-1201.

2.  Padrid P. Feline asthma. Diagnosis and treatment. Vet Clin North Am Small Anim Pract 2000; 30(6): 1279-1293.

3.  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(6); 385-400.

4.  Moise NS, Wiedenkeller D, Yeager AE, et al. Clinical, radiographic, and bronchial cytologic features of cats with bronchial disease: 65 cases (1980-1986). JAVMA 1989; 194: 1467-1473.

5.  Johnson L. Diseases of the bronchus. Textbook of Veterinary Internal Medicine, 5^th ed. Philadelphia: WB Saunders Co; 2000: 1055-1061.

6.  Corcoran BM, Foster DJ, Fuentes VL. Feline asthma syndrome: a retrospective study of the clinical presentation in 29 cats. J Small Anim Pract 1995; 36: 481-488.

7.  Padrid P. Pulmonary diagnostics. Vet Clin North Am Small Anim Pract 2000; 30(6): 1187-1206.

8.  Padrid PA, Feldman BF, Funk K, et al. Cytologic, microbiologic, and biochemical analysis of bronchoalveolar lavage fluid obtained from 24 healthy cats. Am J Vet Res 1991; 52: 1300.

9.  Randolph JF, Moise NS, Scarlett JM, et al. Prevalence of mycoplasmal and ureaplasmal recovery from tracheobronchial lavages and prevalence of mycoplasmal recovery from pharyngeal swab specimens in dogs with or without pulmonary disease. Am J Vet Res 1993; 54: 897.

10. McKiernan BC, Dye JA, Rozanski EA. Tidal breathing flow-volume loops in healthy and bronchitic cats. J Vet Intern Med 1993; 7(6): 388-393.

11. Padrid P, Snook S, Finucane T, et al. Persistent airway hyperresponsiveness and histologic alterations after chronic antigen challenge in cats. Am J Respir Crit Care Med 1995; 151: 184-193.

12. 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.

13. 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(1): 109-115.

14. Dowling PM. Options for treating feline asthma. Vet Med 2001; 353-356.

15. Padrid P. CVT update: Feline asthma. Kirk's Current Veterinary Therapy XIII Small Animal Practice. Philadelphia: WB Saunders Co; 200: 805-810.