Lecture 18 Diseases of the Airway 2

Question 1

What clinical signs would be suggestive of laryngeal disease?

Answer 1

• largely reflect diminished air flow with dyspnoea (= respiratory distress or increased respiratory effort, with both increased rate and depth of respiration) and coughing
• a large percentage of bronchioles must be occluded before clinical signs emerge
• if hypoxaemia develops, may see mucosal pallor or (worse) cyanosis and/or fainting (syncope)
• clinical signs that are particularly suggestive of laryngeal disease are inspiratory stridor (a high-pitched wheezing sound) or roaring caused by air turbulence through the narrowed laryngeal opening) and a change in the voice or loss of voice
• expiration is often rapid and effortless

Question 2

What clinical signs would be suggestive of tracheal disease?

Answer 2

• coughing and dyspnoea are usually the most prominent clinical signs in tracheal, bronchial and bronchiolar disease
• with narrowing of the extra-thoracic trachea, dyspnoea usually occurs during inspiration, inspiratory stridor

Question 3

What clinical signs would you expect to see in an animal with bronchitis?

Answer 3

• with obstruction of the intra-thoracic trachea or bronchitis or bronchiolitis, dyspnoea is more obvious during expiration

Question 4

What clinical signs would you expect to see in an animal with bronchiolitis?

Answer 4

Heaves in horses
• Increased respiratory effort (heaves)
• Chronic cough
• Wheezing
• Exercise intolerance
• Flared nostrils
• Signs are visible at rest
Inflammatory Airway Disease of Horses
• “Mild asthma”
• Not evident or very mild at rest
• Neutrophils, eosinophils and mast cells and mucus in the airways
• +/- Bronchospasm
• Pathogenesis unclear

Question 5

Why is bronchiolitis often clinically silent?

Answer 5

signs may not be evident at rest

Question 6

What are the common congenital malformations of the larynx? In which species are these most often seen?

Answer 6

Hypoplasia of the Epiglottis
- common in pigs and horses 
Subepiglottic Mucosal Cysts
-horses
Tracheal Hypoplasia
- brachycephalic airway syndrome in dogs
Scabbard Trachea
- most common in dogs and horses
Hypoplasia/Dysplasia of Bronchial Cartilage

Question 7

What are possible consequences of a small epiglottis?

Answer 7

• in horses, a hypoplastic epiglottis predisposes to epiglottic entrapment, with the anterior margin of the epiglottis trapped below the aryepiglottic fold. exercise intolerance and chiefly expiratory obstruction to laryngeal air flow
• in horses, a short epiglottis also predisposes to intermittent dorsal displacement of the soft palate

Question 8

In which animals is tracheal hypoplasia most often seen? What is characteristic of a hypoplastic
trachea?

Answer 8

• tracheal hypoplasia can be a component of brachycephalic airway syndrome in dogs
• especially common in English bulldogs and Boston terriers
• the cartilage rings are smaller than normal and typically round in profile rather than C-shaped 
  diffuse reduction in tracheal diameter and decreased air flow

Question 9

What is a scabbard trachea?

Answer 9

• lateral flattening of the trachea into a narrow vertical slit  decreased air flow - most common in dogs and horses

Question 10

To what conditions does hypoplasia/dysplasia of bronchial cartilage predispose?

Answer 10

predisposition to bronchiectasis (permanent dilation of the bronchi), alveolar emphysema and lung lobe torsion

Question 11

What are possible causes of acute laryngeal oedema in domestic animals?

Answer 11

• laryngeal oedema is a feature of acute laryngitis and may also be seen in the acute phases of many systemic infections
• other causes include:
   prolonged barking in dogs
   hyperthermia (with excessive panting) in dogs

Question 12

Why is acute laryngeal edema potentially life-threatening?

Answer 12

• it is potentially life-threatening due to obstruction of air flow

Question 13

Where in the larynx is oedema most likely to be obvious grossly?

Answer 13

usually most prominent over the epiglottis and in the aryepiglottic folds and laryngeal ventricles

Question 14

What is meant by the term laryngeal collapse? Which animals are most likely to be affected?

Answer 14

obstruction of the laryngeal lumen

brachycephalic airway syndrome in dogs

Question 15

What is laryngeal hemiplegia in horses? What clinical signs do affected horses display?

Answer 15

due to distal degeneration of large myelinated axons of the left recurrent laryngeal nerve with
secondary demyelinationunilateral paralysis (laryngeal hemiplegia) and denervation atrophy of intrinsic laryngeal muscles, especially the left dorsal cricoarytenoid muscle  inability to abduct the left arytenoid cartilage and vocal foldpartial airway obstructioninspiratory stridor (“roaring”) and decreased athletic performance

Question 16

In which other species is laryngeal paralysis a common diagnosis? What are possible causes in this species?

Answer 16

Dogs
- laryngeal paralysis is usually bilateral in dogs and may predispose to aspiration pneumonia
- most cases are idiopathic
manifestation of a polyneuropathy or polymyopathy

Question 17

What are some causes of laryngitis and tracheitis in the domestic animals?

Answer 17

viral infection - e.g. canine distemper
bacterial (or mixed) infection - e.g. canine infectious tracheobronchitis (kennel cough), necrotic laryngitis (calf diphtheria), laryngeal abscesses
inhalation of smoke during fires
trauma during intubation
contact trauma associated with increased respiratory effort - e.g. laryngeal contact ulcers
parasites

Question 18

What is calf diphtheria (necrotic laryngitis)?

Answer 18

caused by Fusobacterium
necrophorum in calves, adult cattle, pigs and sheep (often as a secondary
infection following viral or traumatic mucosal ulceration)

Question 19

What is honker syndrome in feedlot cattle?

Answer 19

characterised by at least partial luminal obstruction of the trachea by severe oedema
if severe, can cause asphyxiation and sudden death

Question 20

What is meant by the term tracheal collapse? In which animals is it most often diagnosed?

Answer 20

• tracheal collapse is seen most often in middle-aged toy and miniature dog breeds
• characterised by dorsoventral flattening of the tracheal rings with widening and flaccidity of the
  dorsal trachealis muscle and connective tissue

Question 21

What are potential causes of segmental tracheal collapse?

Answer 21

associated with gradual loss of chondrocytes and of glycosaminoglycans and calcium from the
hyaline cartilage matrix of the tracheal rings, with replacement by fibrous tissue or fibrocartilage
consequence of external compression (e.g. by tumours or enlarged cranial mediastinal lymph nodes) or of peritracheal inflammation
collapse at the level of the thoracic inlet in calves can be a consequence of dystocia

Question 22

What are possible causes of bronchitis in domestic animals?

Answer 22

causes of bronchitis include viruses, bacteria (e.g. Mycoplasma spp.), allergens, inhaled toxic gases
or other irritants, and parasites (e.g. Oslerus osleri in canids)

Question 23

What are known triggers of chronic bronchitis in dogs and cats?

Answer 23

possible triggers include chronic viral infection or chronic exposure to cigarette smoke, sulphur dioxide
or other air pollutants, or dry air
feline bronchial asthma is believed to be induced by allergens

Question 24

What are the structural changes that can lead to airway obstruction in bronchitis?

Answer 24

airway obstruction in bronchitis is caused by a combination of luminal exudate, wall thickening by oedema, inflammation and/or fibrosis, and reflex bronchoconstriction mediated by smooth muscle contraction

Question 25

What is bronchiectasis? What causes it? In which species is it most often seen? What does bronchiectasis look like grossly?

Answer 25

 bronchiectasis = permanent dilation of one or more bronchi
- an uncommon but serious consequence of chronic bronchitis
most commonly seen in cattle with chronic bacterial bronchopneumonia
- also common in horses with heaves (see below) and in pigs, sheep and goats with chronic parasitic bronchitis and bronchopneumonia
-bronchiectasis may cause formation of protruberant lumps in the lungs, with the lumps accentuated by atelectasis of the surrounding parenchyma

Question 26

Why are the distal bronchioles prone to injury?

Answer 26

-vulnerability of ciliated epithelial cells of the bronchioles to oxidative injury
-lack of mucosal goblet cells and submucosal mucus-secreting glands in the distal bronchioles
so that mucociliary clearance does not operate at this level
-lack of supporting cartilage in the bronchioles

Question 27

What are some causes of bronchiolitis in the domestic animals?

Answer 27

viruses, bacteria, nematodes, inhaled allergens, inhaled noxious gases, toxins metabolized by Club cells

Question 28

What are the characteristic microscopic changes that occur in acute and chronic bronchiolitis?

Answer 28

• acute bronchiolitis  necrosis and sloughing of ciliated epithelial cells with mucosal erosion or ulceration and accumulation of exudate and debris in the lumina of the bronchioles
• chronic bronchiolitis, there may be hypertrophy, hyperplasia and/or mucoid metaplasia of the mucosal epithelium

Question 29

What is bronchiolitis fibrosa obliterans?

Answer 29

necrosis of the bronchiolar mucosa and luminal fibrin exudation is followed by ingrowth of granulation
tissue from the submucosa from 7 days post-injurybridging of the lumenpermanent obliteration of part or all of the lumen by scar tissue

Question 30

What is heaves in horses? What is its aetiopathogenesis? Where internationally is heaves a common disease?

Answer 30

• inhalationwidespread neutrophil- and mucus-rich inflammation of the distal bronchioles, possibly as a type 3 or 4 hypersensitivity reaction
• especially common in Europe and North America, particularly in the winter or spring

Question 31

Are tumours of the larynx or trachea common in the domestic animals?

Answer 31

primary tumours of the larynx or trachea are rare in the domestic animals

• squamous cell carcinoma - the most common laryngeal tumour in dogs
• lymphoma in cats