Small airway disease: Bronchitis in dogs and cats (Proceedings)


Small airway disease: Bronchitis in dogs and cats (Proceedings)

Apr 01, 2009

Chronic bronchial disease

Bronchial obstruction can develop due to inflammatory infiltrates (eosinophils, neutrophils, or macrophages) or hypertrophy of bronchial tissues. The result is obstructive airway disease. Increased airway resistance with resultant expiratory dyspnea characterizes obstructive airway disease. Chronic bronchitis in dogs may be caused by congenital abnormalities in the structure and function of airway cilia, parasitic infestation, severe viral or bacterial infection (chronic, untreated periodontal disease), inhalation of noxious irritants, and immune-mediated phenomena. Airway epithelium may hypertrophy, undergo metaplastic change, erode, or ulcerate. Goblet cells and submucosal glands may hypertrophy and produce excessive secretions. Bronchial smooth muscle may hypertrophy. With diffuse airway disease, the airways narrow as a result of endobronchial mucus, edema and hypertrophy of the submucosa and bronchial smooth muscle contraction. The consequences of increased airway resistance in the small bronchi are; increased expiratory pressures result in further airway collapse and expiratory dyspnea and increased work of breathing.

Chronic bronchitis in dogs usually occurs in small and toy breeds 8 years of age or older. The dogs usually have a chronic (greater than 2 months duration) cough that may become productive (terminal retch). The dogs with chronic bronchitis usually have no other systemic signs of disease but may be exercise intolerant. When possible the primary source of infection should be treated. Heartworm disease, periodontal disease and chronic pyoderma may serve as sources for continued infection and should be treated.

Feline bronchial disease

There is no clear terminology for the bronchial obstructive diseases in the cat. Bronchitis is inflammation of the airways. Asthma generally implies a reversible bronchoconstriction related to hypertrophy of smooth muscle in airways, hypertrophy of mucous glands, and infiltrates of eosinophils. Asthma in cats is primarily due to Type I hypersensitivity reactions; the etiology is generally undetermined. Cats with bronchitis not due to asthma generally have infiltrates of neutrophils or macrophages as well as hypertrophy of mucous glands, hyperplasia of goblet cells, excessive mucous, and ultimately fibrosis secondary to chronic inflammation. Etiologies include bacterial infection, mycoplasmosis, viral infection and parasitic infections.

Cats with bronchitis can be of any age; chronic bronchitis usually develops in middle-aged to older cats. There is no obvious breed or gender predilection. Primary presenting complaints include cough, dyspnea, and wheezing. Some cats will have a terminal retch following cough. Physical examination abnormalities include cough, dyspnea, and crackles, and wheezes in the pulmonary tissues. Increased bronchovesicular sounds may be the only abnormality noted on auscultation. If dyspnea occurs, it commonly has a pronounced expiratory component. Open mouth breathing or panting commonly occur during periods of stress.

CBC is generally normal with the exception of eosinophilia in some cats with asthma. Thoracic radiographs reveal primarily a bronchial pattern. Overinflation and air trapping is seen in some dyspneic cats with chronic disease. Air bronchograms are commonly seen in some dyspneic cats with bronchitis due to bacterial infection. Cytology of transtracheal wash samples reveals increased mucus with variable numbers of eosinophils, neutrophils, and macrophages. Bacteria may or may not be visualized. Aerobic and Mycoplasma culture as well as antibiotic susceptibility testing should be performed regardless of the type of inflammatory cell and whether or not bacteria are seen.

Cats with eosinophilic TTW cytology should be assessed for dirofilariasis using adult antigen detection tests or newly developed antibody tests. Fecal flotation (Toxocara and Toxascaris in kittens), Baermann examination of feces (Aelurostrongylus), and fecal sedimentation (Paragonimus) should be performed in cats with eosinophilic TTW cytology particularly if indoor-outdoor and from parasite endemic areas.