Page 353 - Small Animal Internal Medicine, 6th Edition

CHAPTER 21 Disorders of the Trachea and Bronchi 325

Dogs with chronic bronchitis are evaluated because of particularly exposure to smoke, other potential irritants and
loud, harsh cough. Mucus hypersecretion is a component of toxins, or allergens; exposure to infectious agents, such as
VetBooks.ir the disease, but the cough may sound productive or nonpro- boarding or exposure to puppies; and all previous and
current medications and responses to treatment.
ductive. The disease has usually progressed slowly over
On physical examination, increased breath sounds, crack-
months to years, although clients typically report the initial
onset as acute. There should be no systemic signs of illness les, or occasionally wheezes are auscultated in animals with
such as anorexia or weight loss. As the disease progresses, chronic bronchitis. End-expiratory clicks caused by main-
exercise intolerance becomes evident; then incessant cough- stem bronchial or intrathoracic tracheal collapse may be
ing or overt respiratory distress is seen. heard in animals with advanced disease. A prominent or split
Potential complications of chronic bronchitis include second heart sound occurs in animals with secondary pul-
bacterial or mycoplasmal infection, tracheobronchomalacia monary hypertension. Dogs with respiratory distress (end-
(discussed later in this chapter), pulmonary hypertension stage disease) characteristically show marked expiratory
(see Chapter 22), and bronchiectasis. Bronchiectasis is the efforts because of narrowing and collapse of the intrathoracic
term for permanent dilation of the airways (Fig. 21.2; see large airways. The presence of a fever or other systemic signs
also Fig. 20.4). Bronchiectasis can be present secondary to is suggestive of other disease, such as bacterial pneumonia.
other causes of chronic airway inflammation or airway
obstruction, and in association with certain congenital dis- Diagnosis
orders such as ciliary dyskinesia (i.e., immotile cilia syn- Canine chronic bronchitis is defined as a cough that occurs
drome). Bronchiectasis caused by traction on the airways, on most days of 2 or more consecutive months in the
rather than bronchial disease, can be seen with idiopathic past year in the absence of other active disease. Therefore
pulmonary fibrosis. Generally, all the major airways are chronic bronchitis is diagnosed on the basis of not only
dilated in dogs with bronchiectasis, but occasionally the con- clinical signs but also the elimination of other diseases from
dition is localized. Recurrent bacterial infection and overt the list of differential diagnoses (see Box 21.3). The pos-
bacterial pneumonia are common complications in dogs sibility of secondary or concurrent disease complicates this
with bronchiectasis. simple definition.
Dogs with chronic bronchitis are often brought to a vet-
erinarian because of a sudden exacerbation of signs. The
change in signs may result from transient worsening of the
chronic bronchitis, perhaps after a period of unusual excite- BOX 21.3
ment, stress, or exposure to irritants or allergens; from a Diagnostic Considerations for Dogs With Signs
secondary complication, such as bacterial infection; or from Consistent With Canine Chronic Bronchitis
the development of a concurrent disease, such as left atrial
enlargement or heart failure (Box 21.3). In addition to Other Active Disease (Rather Than Canine Chronic
providing a routine complete history, the client should be Bronchitis)
carefully questioned about the character of the cough and Bacterial infection
the progression of signs. Detailed information should be Mycoplasmal infection
obtained regarding the following: environmental conditions, Left atrial enlargement
Pulmonary parasites
Heartworm disease
Allergic bronchitis
Neoplasia
Foreign body
Chronic aspiration
Gastroesophageal reflux*
Potential Complications of Canine Chronic Bronchitis
Tracheobronchomalacia
Pulmonary hypertension
Bacterial infection
Mycoplasmal infection
Bronchiectasis

Most Common Concurrent Cardiopulmonary Diseases
Tracheobronchomalacia
FIG 21.2 Left atrial enlargement
Photomicrograph of a lung biopsy specimen from a dog Heart failure
with severe bronchiectasis. The airways are filled with
exudate and are greatly dilated (hematoxylin and eosin *Gastroesophageal reflux is a common cause of chronic cough in
[H&E] stain). people. Documentation in dogs and cats is limited.