Medicine
Canine Chronic Bronchitis
What is Chronic Bronchitis?
Chronic bronchitis is a long-standing inflammatory condition of the lower airways, characterised by persistent cough lasting more than two months without other identifiable causes. It is most common in middle-aged to older dogs and often small breeds.
- Primary mechanism: Chronic inflammation of bronchi leading to mucosal thickening, goblet cell hyperplasia, and excess mucus production. The underlying primary cause is unclear with most cases being detected in the later stages.
- Contributing factors:
- Environmental irritants (smoke, dust, aerosols)
- Secondary infections
- Aerodigestive disorders and gastro-oesophageal reflux (GERD)
- Progressive cycle: Persistent inflammation → airway remodelling → irreversible changes (bronchiectasis and bronchomalacia) → predisposition to secondary infections.
Clinical Signs
- Chronic cough (>2 months), often non-productive; however, this can vary depending on secondary infections.
- Exercise intolerance
- Wheezing or harsh lung sounds
Differential Diagnoses
- Infectious tracheobronchitis (kennel cough)
- Angiostrongyliasis
- Pneumonia/aerodigestive disorders
- Pulmonary neoplasia
- Cardiac disease (however this is unlikely to cause chronic coughing in the absence of concurrent bronchial/pulmonary disease)
- Tracheal/bronchial collapse
- Foreign body aspiration
- Eosinophilic bronchopneumopathy
Diagnosis
Diagnosis is predominantly based on excluding alternative diagnoses.
Initial investigation
- History & Physical Exam: Persistent cough, absence of systemic illness.
- Thoracic Radiographs: Bronchial pattern (donuts and tramlines).
- Basic Bloodwork: Rule out systemic disease, assess for eosinophilia
- AngioDetect +/- Dirofilaria testing based on history
- Functional laryngeal exam
Advanced Diagnostics
- CT Imaging: Detailed airway and parenchymal assessment to assess degree of pathology and exclude alternative differentials.
- Bronchoscopy: Direct visualisation of airway inflammation, mucus. Assess for bronchial/tracheal collapse. Guided sampling.
- Bronchoalveolar Lavage (BAL): Cytology and culture for infection +/- infectious disease PCRs.
- Echocardiography: Assess for concurrent cardiac disease and pulmonary hypertension
When to Refer?
- Persistent cough despite empirical therapy
- Suspected complications (pneumonia, severe airway collapse; concurrent cardiac disease)
- Need for bronchoscopy/BAL or advanced imaging to confirm diagnosis and screen of secondary infections.
Management
GOALS – avoid exacerbating factors; reduce inflammation; decrease the clinical signs (coughing); improve exercise capacity and slow progression where possible.
- Environmental control and supportive management
- Avoid smoke, aerosols, dust.
- Manage exercise and excitement – limit excessive barking.
- Harness to avoid pressure on the neck via collar.
- Weight Management
- Nebulisation and airway humidification to reduce mucus viscosity.
- Medication
- Anti-inflammatory doses of corticosteroids (oral or inhaled) – reduce bronchial inflammation to decrease mucus hypersecretion and mucosal thickening.
- Bronchodilators (e.g., theophylline) – care if using without excluding secondary infection as this bronchodilation theoretically could lead to further dissemination through the lungs. Also, the majority of pathology is inflammatory with less contribution from bronchospasm vs humans.
- Anti-tussives – codeine, opioids (butorphanol, lofenoxal)
- Antibiotics only if secondary infection confirmed on cytology/culture
Key Points for Referring Vets
- Chronic bronchitis is a diagnosis of exclusion requiring advanced imaging and sampling to evaluate for differential diagnoses.
- Criteria for diagnosis:
- Chronic cough >2 months
- Evidence of excessive mucus
- Exclusion of other causes
- Criteria for diagnosis:
- Given the long term and progressive nature of the disease, ideally early investigation is advised to exclude alternative differentials and target therapy with the aim of delaying progression and optimizing quality of life.