Definition

Bronchiectasis is pathologically defined as an abnormal dilatation and distortion of subsegmental airways, due to destruction of the elastic and muscular components of the bronchial walls. Several congenital or acquired conditions that lead to a cycle of chronic airway infection and inflammation may result in bronchiectatic changes.

Pathogenesis and Etiology

Focal bronchiectasis most often results from foreign body aspiration. Diffuse bronchiectasis often occurs subsequent to aspiration or inhalation injury, primary ciliary dyskinesia, infection with Bordetella bronchiseptica or with Pneumocystis carinii, eosinophilic bronchopneumopathy (EBP), chronic bronchitis (or chronic inflammatory airway disease IAD) and potentially, allergic bronchopulmonary aspergillosis.^1,2 In most dogs with bronchiectasis, affected airways are partially obstructed by purulent or viscid exudate. It is suspected that dilation greatly interferes with normal airway clearance. Dysfunction of mucociliary clearance, in turns, allows pooling of mucus, exudates, and microbes, and secondary infection stimulates a host inflammatory response, creating a vicious cycle of further damage to the airway wall and predisposition to recurrent bronchopulmonary infections. It has been suggested that bronchiectasis might be related to enzymatic products of inflammatory cells and aberrant cytokine response. However, other mechanisms probably exist, since there are dogs with bronchiectasis with no mucous plugging in the airway.²

Airway collapse (bronchomalacia) is associated with bronchiectasis in part of the dogs, in particular those diagnosed with EBP and IAD^1,2 while in other cases, bronchiectatic airways are rigid and do not collapse. Bronchiectasis has been described in a limited number of dogs with bronchomalacia.³ The relationship between bronchiectasis and airway collapse is unclear. It has been suggested that airway inflammation could potentiate airway collapse, but this has not been proven.

Clinical Signs and Diagnosis

There appears to be a breed predilection since bronchiectasis is more prevalent in certain breeds such as the American cocker spaniel, the miniature poodle, the Siberian husky, or English springer spaniel. Most dogs with bronchiectasis are 7 years or older.¹

Clinical signs likely reflect the underlying disease process, and generally include cough, gag, tachypnea, dyspnea, and occasionally fever.

Bronchiectasis can be detected by thoracic radiography, high resolution computed tomography (HRCT), or bronchoscopy. In humans, HRCT is considered the gold standard. In dogs, HRCT is increasingly used to investigate respiratory diseases in dogs and CT features of bronchiectasis have been described and include lack of airway tapering and bronchoarterial ratio >2.4. Survey thoracic radiography is not a very sensitive technique for evaluation of bronchiectatic changes and bronchography is no more used. Bronchoscopy is helpful to recognize/visualize bronchiectatic lesions.² it also enables collection of samples, in an attempt to identify any primary cause.

Management

Therapeutic considerations are the same as for chronic bronchitis, but the disease is more difficult to control. The goal of therapy is to control clinical signs, treat, or even prevent bacterial infections. Addressing the primary underlying pathological process is vital to attempt to slow the progression of destruction of the bronchial walls. Despite substantial clinical abnormalities, dogs with bronchiectasis may survive for years. Patients with focal bronchiectasis are exceptions since surgical resection of the affected lung lobe may be curative.

Take Home Message

Bronchiectasis is a sequela that can be found in dogs, subsequently to underlying respiratory conditions, such as EBP, foreign body aspiration, aspiration or inhalation injury, primary ciliary dyskinesia, infection with Bordetella bronchiseptica or with Pneumocystis carinii or chronic inflammatory airway disease.

Management includes detection and adequate treatment of a possible underlying disease together with symptomatic treatment of the chronic condition, including long-term management of airway secretions, inflammation, and infection.

References

1.  Hawkins EC, Basseches J, Berry CR, Stebbins ME, Ferris KK. Demographic, clinical, and radiographic features of bronchiectasis in dogs: 316 cases (1988–2000). J Am Vet Med Assoc. 2003;223(11):1628–1635.

2.  Johnson LR, Johnson EG, Vernau W, Kass PH, Byrne BA. Bronchoscopy, imaging, and concurrent diseases in dogs with bronchiectasis: (2003–2014). J Vet Intern Med. 2016;30(1):247–254.

3.  Johnson LR, Pollard RE. Tracheal collapse and bronchomalacia dogs: 58 cases (7/2001–1/2008). J Vet Intern Med. 2010;24(2):298–305.

4.  Cannon MS, Johnson LR, Pesavento PA, Kass PH, Wisner ER. Quantitative and qualitative computed tomographic characteristics of bronchiectasis in 12 dogs. Vet Radiol Ultrasound. 2013;54(4):351–357.