Differential diagnoses for chronic coughing include disease processes associated with the airway (including the larynx and conducting airways), lower airways/parenchyma, and, occasionally, pleural space. Abnormalities associated with the airways include tracheobronchomalacia, chronic bronchitis, eosinophilic lung disease, aspiration, foreign bodies, neoplasia, infection (eg, bacterial, parasitic, protozoal, viral), and compression (eg, tracheobronchial lymph nodes, cardiomegaly). Abnormalities associated with the parenchyma include pneumonia (eg, bacterial, aspiration, foreign body, fungal, eosinophilic, interstitial) and neoplasia. Rarely, chronic effusions of the pleural space (most notably chylothorax or neoplastic effusions) may be associated with a cough.
Primary differential diagnoses for Cici were bronchomalacia and chronic bronchitis based on expiratory effort and crackles. Tracheal collapse and cardiomegaly were additional possibilities based on her breed and examination findings.1
Serum chemistry profile and CBC results were normal, and heartworm antigen test results were negative. Thoracic radiography (right lateral, left lateral, ventrodorsal) revealed a diffuse bronchial pattern but was otherwise unremarkable with no cardiomegaly (vertebral left atrial size, 2.1 [normal, 1.4-2.2]; vertebral heart scale, 9 [normal, 8.7-10.7]) or observable airway collapse (Figure 1). Arterial blood gas showed partial pressure of arterial oxygen 97 mm Hg (normal, 81-103 mm Hg). Echocardiography revealed myxomatous mitral valve degeneration (B1) with no evidence of pulmonary hypertension.2 Laryngoscopy/bronchoscopy showed moderate mucosal irregularity and increased mucus of the lobar bronchi (Figure 2) with normal laryngeal function. Concurrent dynamic bronchial collapse of the left and right mainstem bronchi (grade II/III) was observed (Figure 3).3 Bronchoalveolar lavage was performed and submitted for cytologic evaluation and aerobic culture. Cytology revealed nonseptic neutrophilic inflammation (Figure 4); aerobic culture was negative.
Chronic bronchitis was diagnosed based on airway inflammation, history of chronic coughing, physical examination findings, thoracic radiography results, and lack of other observable structural pathology (Table).