Bronchomalacia, characterized by weakness of bronchial walls, is a relatively uncommon cause of airways disease in dogs associated with tracheal collapse and bronchitis and is commonly observed in overweight or obese dogs.
The disease is caused a deficiency of cartilage in subsegmental bronchi, leading to distal airway collapse and bronchiectasis.
In humans, bronchomalacia may occur as a congenital disease (Williams–Campbell syndrome), but in dogs is usually secondary to chronic inflammatory changes within bronchi and bronchioles.
In dogs with bronchomalacia, the compliant bronchi collapse during coughing, leading to poor airway drainage. Subsequently, progressive obstructive disease develops, causing hyperinflation of the lung and segmental or lobar collapse. Recurrent destruction of the bronchial tree and inadequate clearance of mucus result in further damage to the lung parenchyma.
It was thought bronchomalacia was associated with congestive heart failure resulting in enlargement of the right atrium with secondary compression of left-sided bronchi, but this hypothesis is yet to be proven.
There is however evidence that chronic inflammation of the bronchi does predispose to bronchial collapse, resulting in coughing associated with this condition.
Clinically affected dogs often present with a mild, wheezing, chronic cough and pulmonary crackles on auscultation. A history of chronic coughing and intermittent pneumonia may be reported.
Radiographically, collapse of the right middle and left cranial lung lobes are visualized most commonly.
Tracheobronchial lavage may indicate secondary bacterial infections.
Symptomatic relief may be afforded with antioxidants such as N-acetylcysteine and bronchodilators such as terbutaline. Use of corticosteroids, particularly inhalants such as beclomethasone, may exacerbate bronchomalacia and are contraindicated.
Prognosis is guarded in severely affected canine patients.
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