Diseases of the pharynx and oesophagus

Question 1

Describe the anatomical components of the swallowing mechanism

Answer 1

1. 31 pairs of striated muscles
2. 5 cranial nerves - sensory and motor fibres
   
   • Trigeminal
   • Facial
   • Glossopharyngeal
   • Vagus nerve
   • Hypoglossal (motor fibres only)
3. Swallowing centre in the reticular formation of the brainstem
4. Pharynx - anatomical boundary
5. Oesophagus

Question 2

Describe the phases of swallowing up until the bolus passages into the stomach.

Answer 2

1. Oral preparatory phase
   
   • voluntary process - mastication and salivation.
   • Starts to break down the food and lubricate for passage
   • Food bolus is modified and perpared for swallowing
2. Oral phase
   
   • Tongue, jaw and hyoid muscles are involved
   • Bolus is moved caudally from the tongue to the pharynx
3. Pharyngeal phase
   
   • Begins as bolus reaches the tonsils
   • Soft palate lifts to prevent retrograde movement into the nasopharynx
   • Elevation and rostral movement of the layynx and hyoid
   • Retroflexion of the epiglottis and closure of the vocal folds
   • Synchronised contraction of the middle and inferior constrictor muscles together with relaxtion of the cricopharyngeus muscle (most of the upper oesophageal sphincter)
4. Oesophageal phase
   
   • Involuntary with primary peristaltic wave induced by swallowing.
   • Bolus induced secondary peristalsis distension of the lumen
   • Relaxation of the lower oesophageal sphincter ahead of the bolus helps reduce pressure to blous movement

Question 3

Note the major anatomical sites where disruption to anatomy or function can contribute to a swallowing disorder

Answer 3

• Oral / dental disease can contribute to difficulty with the oral prepatory phase

Swallowing

1. Brain stem disease
2. Cranial nerve dysfunction
3. Laryngeal diseases - failure of airway protection
4. Oropharyngeal muscles - weakness
5. Oropharyngeal / UES muscles - asynchrony
6. Oesophagus - Inflammatory disease, foreign bodies, musclular weakness, stricture.
7. Lower oesophageal sphincter diseases including herniation and other causes of GORD

Question 4

Describe the pathophysiological end result of the myriad causes for oropharyngeal dysphagia

Answer 4

1. Abnormalities of bolus transport
   
   • pharyngeal pump failure - weakness
   • asynchrony - neurogenic
   • pharyngeal outflow obstruction (achlaisa, tumour, foreign body)
2. Abnormalities of airway protection

Question 5

List the common signs of oropharyngeal dysphagia

Answer 5

1. Food falling from the mouth
2. Repetitive swallowing
3. Gagging or retching
4. Nasal regurgitation
5. Swallow-related coughing
6. Recurrent pneumonia

Question 6

Note the signs commonly seen with oesophageal dysphagia

Answer 6

1. Regurgitation - food or water (or saliva)
2. Odynophagia - painful swallowing
3. Repeated swallowing attempts
4. Excessive ptyalism

Question 7

Describe the process of performing a complete video fluorscopy study

Note the important components that need to be assessed

Answer 7

• Ideally performed in sternal or standing as lateral recumbency can lead to retention of food or at least delayed passage within the cervical oesophagus

1. Five swallows of 5-10 ml liquid barium
2. Five swallows of barium soaked canned food
3. Five swallows of barium soaked kibble

• Frame by frame analysis (at 30 frames per second) which starts as the epiglottis covers the larynx
• Swallow completed when the epiglottis is observed to re-open - typically after 5-6 frames in a healthy dog
• Pharyngeal constriction ratio can be used to assess the change in pharyngeal area - estimate of pharyngeal strength.
• Oesophageal passage of the bolus
  
  • Timing helps to assess the strength of the peristaltic wave
  • Strictures/narrowing can be observed
• Emptying into the stomach through the LES
• Observation for gastro-oesophageal reflux

Question 8

List the various diagnostic tests that can be employed to assess swallowing.

Note when each of the tests can be of specific diagnostic value

Answer 8

1. Laboratory testing: CK, TT4, AChR Ab titre, 2M Ab titre
   
   • Myositis - generalise or focal
   • Myaesthenia gravis
2. Cervical and thoracic radiography
   
   • Megaoesophagus
   • Foreign body
3. Video-fluoroscopy
   
   • Motility disorders
   • Functional swallowing disorders including:
     
     • asynchony (cricopharyngeal achlasia)
     • pharyngeal weakness
   • May help diagnose oesophageal stricture
   • May be useful for assessment of hiatal hernia and LES disorders
4. Endoscopy
   
   • Foreign body
   • Stricutre
   • Oesophagitis
   • LES dysfunction including hiatal hernia
5. Electrodiagnostic testing
   
   • May be useful but not specific for myopathic and neuropathic disease processes.
6. Muscle and Nerve biopsy
   
   • May be diagnostic for masticatory muscle myositis
7. MRI
   
   • Useful for the diagnosis of inflammatory myopathies including MMM and to help select biopsy sites
   • Neoplasia
8. Oesophageal Manometry
9. Oesophageal pH and impedence testing.

Question 9

List the potential causes for oesophagitis with note of the relevant pathophysiology

Answer 9

1. Gastro-oesophageal reflux
   
   • Due to hiatal herniation or anaesthesia
   • 46-65% of strictures
   • Relaxation of the LES is mediated by non-adrenoergeic and non-cholinergic pathways
   • Relaxation of LES occurs with many sedatives and inhaled anaesthetic agents
2. Chronic vomiting
   
   • chronic and repetitive exposure of the mucosa to gastric acid and pepsin
3. Ingestion of caustic agents
4. Foreign body - direct mechanical trauma to the oesophageal mucosa. Pressure necrosis is a major contributing factor to mucosal erosion
5. Embrittled feeding tubes
6. Doxycycline or clindamycin lodgement in cats

Question 10

Describe the management of dogs with mild to severe oesophagitis

Answer 10

Mild oesophagitis

• Typically self limiting and managed supportively
• Small feeds frequently
• Fat-restricted meals - helps promote gastric emptying

Moderate to severe - clinical signs of dysphagia or odynophagia

• Identify any inciting cause
• Supportive care as required
• Proton pump inhibitors - more effective the H2 blockers
• Sucralfate provided as a slurry
• Cisapride or metoclopramide - promote gastric emptying and enhance LES tone
• Antibiotics if there is concurrent aspiration pneumonia

Question 11

List the causes of diffuse oesophageal dilatation / megaoesophagus

Answer 11

1. Congenital megaoesophagus
2. Idiopathic megaoesophagus
3. Focal myasthenia gravis
4. Myositis / myopathy - focal or diffuse
5. Polyneuropathy
6. Endocrine disease - Hypoadrenocorticism / hypothyroidism
7. Toxin ingestion - botulism
8. Severe oesophagitis
9. Dysautonomia

Question 12

Briefly note the management recommendations for dogs with acquired megaoesophagus

Answer 12

1. Attempt to identify an underlying cause
   
   • Blood tests - CK, cortisol (or stimulation test), AChR Ab titre,
   • Thoracic radiographs / fluoroscopy / endoscopy / EMG
2. Treat specific underlying cause - consider pyridostigmine trial while awaiting AChR Ab titre pending signalment
3. Small frequent meals from an upright position
   
   • Bailey chair may help
4. Varying the consistency of the food to suit the dog
5. Placement of a PEG tube if necessary - temporary or permanent
6. Monitor for aspiration pneumonia - pre-emptively treat with antibiotics with consistent clinical signs