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Dynamic pharyngeal disorder
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Evaluating the equine upper airway
- For centuries only clinical assessment possible (ie noise and poor performance)
- In the 19th century better pathology techniques allowed identification of specific diseases eg laryngeal hemiplegia
- Early part of 20th century rigid endoscopy allowed recognition of several conditions but general reluctance to use the technique
- Late 1960s fibreoptic endoscopy encouraged examination and many more conditions identified
- Video-endoscopy afforded even better images and allowed the possibility of easily obtaining and recording moving images
- Video-endoscopy combined with exercising horses on a treadmill allowed recognition of several previously unknown “dynamic” causes of upper airway obstruction
- Respiratory physiologists had the opportunity to evaluate respiratory performance during exercise
- Remote dynamic endoscopy allowed endoscopy of horses during free exercise diagnostic procedure
- Conditions which can be diagnosed by a thorough clinical examination
- Conditions which can be diagnosed by endoscopy during quiet respiration
- Conditions which require dynamic endoscopy
- Conditions which require other imaging modalities for an accurate diagnosis
Common upper airway disease syndromes
- Conditions causing nasal discharge
- Conditions causing epistaxis
- Conditions causing dysphagia
- Conditions causing respiratory obstruction
Clinical assessment of the upper airway
- Nasal discharge, haemorrhage, food?
- Facial distortion?
- Swelling of pharynx?
- Airflow through both nostrils?
- Respiratory stridor at rest?
- Respiratory noise at exercise?
- Exercise intolerance?
- Laryngeal palpation
Respiratory stridor during quiet breathing
- Audible noise
- May be dyspnoea
- Check patency of external nares and block off each
- May be facial asymmetry
- May be swelling in pharyngeal region
Relationship of respiratory cycle to limb movement at the gallop
- Direct 1:1 relationship between limb movement and respiratory cycle
- Expiration triggered when fore limbs hit the ground
- Some horses breathe 2:1 at exercise (untrained yearlings) - probable relationship with respiratory obstruction?
Respiratory noise at exercise
- Expiratory noises are common (“high blowing”)
- Inspiration is typically quiet although a faint sound may sometimes be heard from normal horse
- An inspiratory “whistle” or “roar” is caused by airflow turbulence from upper airway obstruction
Respiratory noise at exercise
- Horses should be exercised at the canter to determine inspiratory and expiratory phases of the respiratory cycle
- Most causes of upper airway obstruction result in adventitious inspiratory noises (“whistle”, “roar”), or “gurgle” (expiratory)
- The frequency of a characteristic whistle is most easily heard by the female ear and by men under the age of 40 years!
- If exercising on the lunge it is important to use both reins
Exercise intolerance
- Often difficult to assess
- Everyone assumes their horse is a champion!
- Occasionally can be very obvious
- Never forget an athlete is a mosaic of many tiles including natural talent
- Ability of jockey often overlooked
Laryngeal palpation
- A skill that takes practice
- Use fingers to evaluate laryngeal symmetry
- Intrinsic muscles (cad)
- Cartilaginous architecture
- Post-exercise fremitus and right arytenoid depression
- For what conditions does laryngeal palpation facilitate a diagnosis?
- Previous laryngeal surgery laryngotomy scar
- Recurrent laryngeal neuropathy muscular atrophy
- 4th branchial arch anomaly cartilage asymmetry
Nasal discharge
- Most horses with pharyngeal or laryngeal obstruction have little or no nasal discharge
- Cases of pharyngeal abscess or guttural pouch empyema often have a bilateral purulent nasal discharge (strangles!)
- Unilateral discharges tend to originate from the nasal passages or paranasal sinuses
- Coincidental exercise-induced pulmonary haemorrhage may confuse the diagnosis
Endoscopy during quiet respiration
- Fibreoptic endoscopy now routine in equine practice
- Facilitates diagnosis in many cases of respiratory obstruction
- There are diagnostic limitations in many cases of respiratory noise at exercise (racehorses)
Pharyngeal and laryngeal conditions readily diagnosed by endoscopy at rest
- Pharyngeal mass (tumour, cyst, guttural pouch swelling)
- Epiglottal entrapment
- Subepiglottal cyst
- Advanced recurrent laryngeal neuropathy
- 4th branchial arch anomaly (most cases)
Guttural pouch tympany or empyema
- Often externally visible swelling of throat
- Typically snoring respiration
- Sometimes dysphagia
- Tympany noted typically just after birth
- Empyema may be associated strangles or any bacterial respiratory infection
Guttural pouch empyema
Guttural pouch tympany
- Newborn foals or younger horses
- More common in arabians and fillies
- Visible swelling of parotid area usually intermittent
- May be bilateral
- Snoring respiration +/- dysphagia
Diagnostic difficulties in tympanitic foals
- Some foals may be frankly dyspnoeic (tracheotomy?)
- Endoscopic examination does not allow easy differentiation of affected side (catheter deflation)
- Radiography diagnostic but determining affected side is difficult
Pharyngeal neoplasia
- Typically older horse (except lymphoma)
- Often advanced stage by time of diagnosis
- Typically invasive and destructive
- Respiratory obstruction is commonest sign (+/-dysphagia, epistaxis)
Epiglottal entrapment
- Loosely attached ventral epiglottal mucosa (swallowing)
- Dorsally displaced (usually persistent)
- Can be asymptomatic
- Usually responsible for an inspiratory noise or ddsp
Subepiglottal cyst
- Typically these congenital cysts sit in the subepiglottal mucosa
- Occasionally found elsewhere
- Small cysts are asymptomatic but large cysts cause respiratory obstruction and sometimes dysphagia in young foals
Arytenoid chondritis
- Typically swelling on medial face of arytenoid or irregular arytenoid enlargement
- May appear at first glance like hemiplegia
- Reduction in movement is due to cartilage distortion
4th branchial arch anomalies
- Congenital defect
- Palpation often reveals cartilage asymmetry
- Endoscopy can be diagnostic but may reveal little
- Laryngeal cartilage deformity and cricopharyngeal muscle hypoplasia
- Often asymmetrical and right-sided
‘4 bad’ endoscopic features
- May appear normal!
- Rostral displacement of palatopharyngeal arch
- Right-sided laryngeal dysfunction
- Loss of rostral oesophageal spincter (cricpharyngeal muscles)
Advanced recurrent laryngeal neuropathy
- Obvious reduction in movement of left side of larynx noted by endoscopy during quiet respiration
- Marked asymmetry of rima glottidis
Dynamic endoscopy
- Originally on high speed treadmill
- Now by remote endoscopy
- Valuable when a mismatch between endoscopy at rest and respiratory noise produced during exercise
- Many conditions now identified which can only be diagnosed by dynamic endoscopy at exercise
What can dynamic endoscopy reveal about the URT during fast exercise?
- Intermittent ddsp
- Intermittent epiglottal entrapment
- Aryepiglottal fold impingement
- Vocal cord collapse
- Pharyngeal collapse
- Cricotracheal ligament impingement
- Epiglottal retroversion
- Dynamic laryngeal collapse (rln)
Intermittent dorsal displacement of the soft palate during galloping
- Easy to recognise if full ddsp
- Prodromal “billowing” (instability) is a more subjective diagnosis
- Some horses seem to displace after a gallop
- If exercise inadequate or no racing stress horse may not displace
- Ddsp during resting endoscopy of very debatable significance (? barakzai and dixon evj 2011?)
Intermittent epiglottal entrapment
- May be noted during resting endoscopy (ulcer?)
- Typically triggered by swallowing reflex
- May not occur during every exercise period
- May be very transient
- Probably just as likely to be identified during endoscopy at rest
Vocal cord collapse
- Can not be diagnosed without dynamic endoscopy
- Typically a consequence of recurrent laryngeal neuropathy (or cricothyroid muscle dysfunction? holcombe et al 2006)
- Of greatest significance in absence of arytenoid collapse
- Represents more of a therapeutic dilemma than a diagnostic problem
Nasopharyngeal collapse
- Can not be diagnosed without dynamic endoscopy
- May be dorsal, dorsolateral or lateral impingement
- May be associated with other URT problems
- Typically racehorse or show horse
- Pharyngeal lymphoid hyperplasia has no effect on function at exercise and no value as a predictor of collapse
Aryepiglottal fold instability and medial displacement
- Can not be diagnosed by endoscopy at rest
- Typically a problem in racing thoroughbreds
- May be associated with other airway problems
Epiglottal retroversion
- Can only be diagnosed by dynamic endoscopy
- Seen in many types of horse
- Loud “pig-like” inspiratory noise
- Usually affects performance
Recurrent laryngeal neuropathy
- At rest basically a symmetrical larynx
- At exercise severe dynamic left-sided laryngeal collaps
Cases in which other imaging modalities allow or help confirm a diagnosis
- Pharyngeal cysts not clearly identified by endoscopy (may be hidden below soft palate)
- Guttural pouch tympany
- 4th branchial arch anomaly
- Recurrent laryngeal neuropathy
Guttural pouch tympany
- Lateral radiographic image demonstrates an enlarged pouch
- A dv image might help differentiate between left and right pouches but is difficult
- Allows identification of any fluid present
- CT would also be useful
4th branchial arch anomaly
- Various anomalies encountered
- Cricopharyngeus muscles usually hypoplastic or even aplastic
- Cranial oesophageal sphincter
- May be unilateral or bilateral
- Air in cranial oesophagus visible radiologically
- Lateral radiographic image often diagnostic
- Characteristic eructation
Bilateral 4 bad case
- Young horse
- Loud inspiratory “roar”
- Exercise intolerance
- Dynamic endoscopy suggestive of restricted abduction
- CT confirmed diagnosis of bilateral 4 bad
Laryngeal ultrasound
- Transcutaneous probe held firmly over laryngeal region
- Assessing cricoarytenoideus lateralis muscle
- Gives a good idea of health of cricoarytenoideus dorsalis
- Comparing left and right
- Denervated muscle becomes scarred and much more echodense than normal musculature
Take home messages
- Investigating equine pharyngeal and laryngeal disease involves a variety of techniques and skills
- Modern imaging has revolutionised our understanding of the disease processes
- One must be aware of the limitations of the various techniques to ensure the most appropriate are used
- Management of client expectation is absolutely critical
Get access to all handy features included in the IVIS website
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