Comorbid Conditions, Diagnostic Conundrums, and Differential Diagnoses
Comorbid conditions include concurrent bronchial collapse, laryngeal paralysis, and bronchiectasis (Bottero et al. 2013, Johnson and Pollard 2010; Chisnell and Pardo 2015). Airway inflammatory changes as determined by BAL cytology is seen in a large proportion of dogs with airway collapse (Johnson and Pollard 2010; Singh et al.
2012), but whether there is a causal relation, or whether it represents a concurrent, but independent condition, requires further investigation. Ideally, all patients investigated for collapsing airway disease should also be investigated for chronic bronchitis or inflammatory airway disease.Patients with tracheal and bronchial collapse potentially have decreased mucociliary clearance mechanisms, leading to increased risk for secondary bacterial bronchitis and bronchopneumonia; although concurrent airway infections in newly diagnosed cases of tracheal collapse is not a common finding (Johnson and Pollard 2010). Acute infectious tracheobronchitis may be mistaken for tracheal collapse and patients with tracheal collapse can become infected with Bordetella bronchiseptica.
Mitral valve regurgitation caused by myxomatous degeneration may result in coughing as a result of left atrial enlargement with compression of the left main stem bronchi without the dog being in congestive heart failure. The collapsing trachea patient in congestive heart failure is expected to have an increased sleeping respiratory rate; and increased serum NT-proBNP concentrations help differentiate cardiac causes of respiratory signs from respiratory diseases (Oyama et al. 2009; Schober et al. 2010; Rishniw et al. 2012; Ferasin et al. 2013). Respiratory sinus arrhythmia is not expected in a patient with congestive heart failure, but may be present in a dog with tracheal collapse and mitral valve regurgitation not in heart failure. Pulmonary hypertension may complicate airway collapse (Bottero et al. 2013) and would need to be addressed as a comorbid condition.
Up to 55 % of dogs may have a co-associated condition at the onset of clinical signs (White and Williams 1994).