Content uploaded by Tom Ahern
Author content
All content in this area was uploaded by Tom Ahern on Mar 05, 2021
Content may be subject to copyright.
10 World Jou rnal of Veterinary Science, 2021, 9, 10-15
E-ISSN: 2310-0796/21 © 2021 Syne rgy Publ ishers
Upper Oesophageal Sphincter Aplasia in Equids: Observations in
Preoperative Patients and a Possible Association with some Cases
of Dorsal Pharyngeal Collapse and Paradoxical Sleep Deprivation
Tom Ahern*
Knockdown Lodge, 17 Keymer Street, Ascot, 6104, Western Australia
Abstract: Upper oesophageal sphincter aplasia and subsequent incompetence had been reported as one element of the
fourth branchial arch defect syndrome and also as a possible sequelae to the placement of a laryngeal abductor
prosthesis. Fourth branchial arch defects were thought to be uncommon and when diagnosed it was more often the
cartilaginous abnormalities with associated arytenoid abductor incompetence that were discussed. As a consequence of
introducing manual assessments of upper oesophageal sphincter tone to the oropharyngeal examination performed prior
to palatoplasty procedures, it was determined that this presentation was more common than previously reported. In
addition and as a result of pre and post operative examin ations a nd history collection there appeared to be a possible
association in some instances w ith cas es of dorsal pharyngea l collapse and paradoxical sleep deprivation.
Keywords: Horse, sleep disorders, upper airway, aerophagia, hiccup.
INTRODUCTION
The upper oesophageal sphincter (UOS) is formed
by elements of the crico and thyro-pharyngeus muscles
[1,2]. Its purpose is to prevent food and water being
returned to the nasopharynx during the process of
deglutition. UOS aplasia and incompetence had been
reported in five horses following prosthetic
laryngoplasty [3]. The suspected etiology in these
cases was intraoperative trauma to either the
musculature or to the neural supply [3]. Chronic
coughing and upper tracheal contamination were
common presenting complaints.
In cases of aplasia, which were one element of
fourth brachial arch defects (4BAD), associated reflux
could precipitate airways contamination with horses
presenting with histories of repeated airways infections
[4-7]. Aerophagia, as a consequence of UOS aplasia in
4BAD horses, could in some cases culminate in
instances of tympanitic colic [2,5].
Most cases of 4BAD were diagnosed when either
rostral displacement of the palatopharyngeal arch
(RDPA) [8,9] was evident on endoscopy or when
laryngeal abductor dysfunction along with palpable
abnormalities of the cricothyroid articulation were
detected [2,4,5]. Cases of right sided abductor
dysfunction were frequently diagnosed as being part of
4BAD condition [4,5].
It was uncommon to see reports where the only
recorded abnormality was that of UOS hypoplasia or
*Address correspondence to this author at the Knockdown Lodge, 17 Keymer
Street, Ascot, 6104, Wester n Austr alia; E-mail: aher nvet@hotmail.com
aplasia. This segment of the 4BAD complex was
normally diagnosed by either utilising radiography to
detect the presence of air in the proximal oesophagus
[4] or with ultrasonography of the larynx which included
the cricopharynx [10]. There were no reports in the
literature of manual assessments of UOS integrity.
Dorsal pharyngeal wall collapse, which could occur
in association with lateral pharyngeal wall collapse or
independently, was regarded as part of the condition
referred to as dynamic pharyngeal collapse (PC) [11-
13]. Causative theories centered around the function
and thence potential dysfunction of the
stylopharyngeus muscle [14,15].
Paradoxical sleep deprivation and with this a
number of possible sequelae including sleep crashing
had drawn interest from researchers in recent times
[16-18]. Many cases of recumbent sleep deprivation
were successfully managed with changes in the horses
environment, choice of guard or companion or with
pain management [16,17]. There were also two case in
which the horses returned to normal recumbent sleep
following upper airways surgery to reduce the impact of
palatal instability on nasopharyngeal airway
competence [19,20].
MATERIALS AND METHOD
A total number of 300 horses which presented for
surgery in an attempt to reduce the incidence of palatal
instability (PI) [21,22] with or without progression to
dorsal displacement of the soft palate (DDSP) [23-25]
were used in this study. All horses underwent a
modified oral palato-pharyngoplasty (OPP) [26,27].
Upper Oesophageal Sphincter Aplasia in Equids World Journal of Veterinary Science, 2021, Vol. 9 11
Assessments of UOS constrictor tone were made
manually by the same operator following the induction
of anaesthesia. The same induction protocol was used
in all cases and examinations were made within 3 to 4
minutes of the horse attaining recumbency. Initially
three fingers (except thumb and little finger) were
inserted into the oesophagus in a triangular formation
(see Figure 1). The most common, and what was then
regarded as a normal response, was when the fingers
were firstly compressed and then held tight. This was
graded as 0. Grades from 1 to 5 reflected progressive
lessening in this response (see Figure 2A). For grades
2 to 5 the fingers were held in a linear arrangement
(see Figure 1A). Grade 5 had been previously recorded
but not in this study. In these cases the operators five
fingers w ere inserted in a linear arrangement with next
to no contractile response. These horses presented
with chronic reflux, nasal return of mucus and green
feed and with repeated airways infections.
The incidence and degree of UOS dysfunction
along with age, gender and breed were recorded (see
Figures 2 and 3). Only grades 2-3 and above were
included in the study in an attempt to remove any
possible variation in contractile response to
anaesthesia. There were however a number of grade
1-2 cases where clinical histories strongly suggested
the presence of UOS incompetence.
Figure 2: A. Grading protocol: Degrees of reduced
contractile tone (palpation).
B. Incidence of varying grades of reduced contractile tone.
Any elements of the presenting histories that were
suggestive of UOS incompetence and or the presence
A B
Figure 1: A. Three digit test for UOS tone. B. Grade 4 - four digit linear.
12 World Jou rnal of Veterina ry Science, 2021, Vol. 9 Tom Ahern
of 4BAD were recorded along with any relevant
findings from endoscopic examinations.
RESULTS
Of the 300 horses included in this study, 284
(94.7%) were Thoroughbreds (TB), 11(3.7%)
Standardbreds (STB) and 5 (1.6%) Warmbloods (WB).
The grading system used in assessing UOS tone or
contractility was developed by the author (see Figure
1A). Forty-six horses (15.3%) were graded greater than
1-2 (see Figure 3).
The incidence in TB’s at 13% was probably a truer
reflection of the incidence of this condition in this
surgical population. The total population figure of
15.3% was heavily influenced by a small number of
STB and WB cases. There appeared to be no gender
bias and little age influence except where case
numbers were limited (5 -11yrs).
Twenty-seven (58%) horses were assessed with
moderate loss of tone (grades 2 -3) , whilst 19 (42%)
were more severe. The numbers of horses declined
with increasing severity of UOS incompetence.
Of the 46 cases graded 2-3 and above, none were
recorded as having (RDPA) [7-9] and only one had
significant laryngeal abductor dysfunction which was
determined to be due to an atrophic thyro-cricoid
articulation (left side) [4-7]. Bilateral dorsal pharyngeal
collapse was evident in three horses, whilst mucus with
feed material in the upper trachea was also present. 1
horse had unilateral collapse.Ten horses had
inflammation of the trachea and bronchi with heavy
mucus loads and feed material present within the
mucus.
In the process of procuring preoperative ‘histories’ a
number of potentially significant symptoms were
recorded. Some of these had been previously reported
as occurring in horses subsequently diagnosed with
4BAD’s whilst others related more to the horses
general behaviour or demure and also their recumbent
sleep habits. As not all horses were investigated
preoperatively with a view to assessing these factors,
their frequencies are therefore unlikely to be a
reflection of their true incidence.
Stable or Yard
Apparent absence of recumbent sleep -7, Cribbing
or crib biting - 5 horses, Mucus/saliva film on drinking
water -2. Green mucus in nostrils -2. Chronic cough -5,
Sleeping in sternal recumbency only -2, Long periods
of recumbency (2-3 hours) often late AM - 2,
Excitement followed by colic (one stallion when calling
to a mare would ingest enough air to initiate colic) - 2,
History of repeated episodes of tympanitic colic - 2, and
noises similar to hiccups - 1.
Behaviour
Somnolent - 5, Somnolent to hyper-reactive - 6
[19,20],
Race/Event and Training Related
Extremely loud inspiratory noises - 8, Extended
recovery (up to 30 minutes) - 8, Flatulence following
exercise - 6, Nasal return of water during mouth wash -
Figure 3: Horses presented for surgery from August 2015 to December 2020. Breed and age distribution
Upper Oesophageal Sphincter Aplasia in Equids World Journal of Veterinary Science, 2021, Vol. 9 13
4. Chronic cough in work - 7. Frequent airways
infections - 4. Curious noises described as trumpet - 3
or flute like - 1. White foamy discharge after work - 3.
There were also peri-operative observations that
may have been related to this condition. On induction,
as the horses head moved ventrally with sedation, a
continuous white mucoid discharge became apparent
in one nostril - 3. Long periods of recumbency/recovery
post anaesthesia (1 to 2 hours) - 7. Saliva from
laryngotomy -2. Copious flatulence on recovery - 5.
Chronic cough (normally only occasional coughing post
operatively) - 3.
Fourth branchial arch defects in full siblings had
been previously reported [28]. In this study two horses
had two half siblings, that had previously been
recorded as having significant UOS incompetence.
Another had two full siblings.
DISCUSSION
It had been reported that approximately two in a
thousand Thoroughbreds were born with a 4BAD [2].
Aides to diagnosis included palpation [5,2],
ultrasonography [10,29], radiography [29], magnetic
resonance imaging (MRI) [30-32], computed
tomography (CT) [31,33] and endoscopy. The more
common indications that would trigger an investigation
into the possibility of a 4BAD being present were
endoscopic evidence of RDPA [7-9], oesophageal
exudate [3], right sided laryngeal abductor dysfunction
[2,6] or a history of tympanitic colic. Others often only
came to light when surgical attempts to abduct the
corniculate process, using a laryngoplasty, failed.
In this study approximately one in seven horses that
presented for palatoplasty surgery had palpable
reductions in UOS contractile response. Given that
DDSP has a reported incidence of 10-20% in TB’s, the
results of this study would suggest a higher incidence
of 4BAD in this breed [2]. Interestingly none of the 46
horses presented with RDPA and only one with a left
sided abductor deficit that was a consequence of an
atrophic crico-thyroid articulation. In addition only two
horses had a history of tympanitic colic whilst five
others had a white foamy or green tinged nasal
discharge suggestive of oesophageal reflux [4,5].
There were four horses with dorsal pharyngeal
collapse (one unilateral and three bilateral) evident on
endoscopy. A previously reported 4BAD case in a pony
presented with gross enlargement of the right crico-
thyroid notch, a resting right sided abductor dysfunction
and dorsal pharyngeal collapse during exercise [37].
Interestingly the right corniculate cartilage was seen to
fully abduct during an exercise test whilst the dorsal
pharynx collapsed. This suggested that a reported
adventitious noise was likely being created by the
pharyngeal collapse rather than the 4BAD [37].
It w as postulated that if dilation of the proximal
oesophagus was to occur during exercise then the
dorsal excursion of the roof of the oesophagus would
apply a positive pressure to the caudal floor of the
guttural pouch. This compression would then create a
positive pressure within the pouch which could then
result in the dorsal wall of the nasopharynx moving
ventrally. Indeed, ventral collapse of the nasopharynx
along with dorsal movement of the soft palate and
epiglottis along with dilation of the proximal
oesophagus were already recognised as being integral
contributors to the pharyngeal ‘stripping wave’ [2]. As
much as the action of the stylo-pharyngeus muscle and
any possible interference to its neural supply had been
postulated as an aetiology for this form of pharyngeal
collapse, to date there appeared to be no evidence to
support this theory [11,13-15].
In two previously published case studies of horses
that had issues with achieving adequate paradoxical
sleep and that subsequently underwent palatoplastys,
UOS constrictor grades of 2-3 had been recorded
[19,20]. At the time these findings were not thought to
be relevant and thus were not mentioned in the
publications.
In this study 11 (24%) of the 46 (Graded 2-3 and
above) cases presented with histories of somnolence
[16]. In 9 of these cases owners reported that they had
never observed the animals in lateral recumbency. The
other 2 horses were often seen in extended (several
hours) periods of recumbency. However in no cases
was 24 hour monitoring carried out so paradoxical
sleep deprivation could not be confirmed.Theoretically
during periods of recumbent sleep reduced muscle
tone along with UOS weakness could trigger proximal
oesophagus dilation. As previously suggested a
resultant positive pressure created within the guttural
pouch could then contribute to the ventral movement of
the dorsal pharyngeal wall. If PI with its dorsal
movement of the soft palate or DDSP were to occur
along with this ventral excursion of the roof of the
nasopharynx, an airway obstruction similar to that
described in human cases of obstructive sleep apnea
(OSA) could ensue [38].
14 World Jou rnal of Veterina ry Science, 2021, Vol. 9 Tom Ahern
In the present study many of the theories presented
lack sufficient evidence other than that of an anecdotal
nature to support them. Further rigorous investigations
would be required to either support or refute these
theories. However from a practical viewpoint it would
be useful if practitioners when encountering cases of
dorsal pharyngeal collapse, other than those
associated with pole flexion, or recumbent sleep
deprivation where aetiologies were unknown, could
include an assessment of UOS structure and
competence in their clinical workups.
REFERENCES
[1] O’Brien JA, Harvey CE, Brodey RS. The esophagus, In:
Anderson NV, Ed. Veterinary G astroenterology. Philadelphia:
Lea & Febiger, 1 980; p. 372.
[2] Lane GJ, Pascoe R. Upper alimentary system. In: Equine
Medicine, Surgery and Reproduction 2nd ed. Philadelphia:
Elsevier, 2012; pp. 2-6.
https://doi.org/10.1016/B978-0-7020-2801-4.00001-8
[3] Barakzai SZ, Dixon PM, Hawkes CS, Cox A, Barnett TP.
Upper oesophageal incompetence in five horses after
prosthetic laryngoplasty. Vet S urg 201 5; 44(2): 150-155.
https://doi.org/10.1111/j.1532-950X.2014.12101.x
[4] Townsend N. Diagnosis and treatment of fourth branchial
arch defects. Equine Vet Edu 2013; 25(6): 278-281.
https://doi.org/10.1111/eve.12036
[5] Lane JG. Fourth branchi al arch defects. In. Proc of 15th Bain
Fallon memorial lect ures. AEVA, Artarmon 1993; pp. 209-
212.
[6] Lane JG. Non-RLN upper respiratory tract disorders found in
a survey of 3497 Thoroughbred yearlings. In: Havemeyer
Foundation Monograph Series, Eds: Dixon PM, R obinson
NE, Wade JE, R&W Publications, Newmarket 2003; pp. 49-
50.
[7] Lane JG. Fo urth branc hial arch defects. I n: Equine
Respiratory Medicine and Surgery, Eds: McGorum BC, Dixon
PM, Robinson NE, Schumacher J, Saunders WB,
Philadelphia. 2007; pp. 467-472.
https://doi.org/10.1016/B978-0-7020-2759-8.50036-2
[8] Goulden BE, Anderson LJ, Davies AS, Barnes GR. Rostral
Displacement of the palatopharyngeal arch: A case report.
Equine Vet J 1976; 8(3): 95-98.
https://doi.org/10.1111/j.2042-3306.1976.tb03305.x
[9] Crabill M, Schumacher J, Walker M. What is your diagnosis?
Rostral displacement of the palatpharyngeal arch. J of the
Am Vet Med Assoc 1994; 204(9): 1347-8.
[10] Chalmers HJ, Cheetham J, Yeager AE, Ducharme NG.
Ultrasonography of the equine larynx. Vet. Radiology and
Ultrasound 2006; 47(5): 476-81.
https://doi.org/10.1111/j.1740-8261.2006.00170.x
[11] Ducharme NG. Dynamic pharyngeal collapse. In: Current
Therapy in Equine Medicine, Vol. 3. Ed: Robinson NE,
Saunders WB, Philadelphia. Pp. 283-285
[12] Kannegieter NJ, Dore ML. Endoscopy of the upper
respiratory tract during treadmill exercise: a clinical study of
100 horses. Aus Vet J 1995; 72( 3): 101-7.
https://doi.org/10.1111/j.1751-0813.1995.tb15020.x
[13] Boyle AG, Martin BB, Davidson EJ, Durando MM, Birks EK.
Dynamic pharyngeal collapse in racehorses. Equine Vet J
Suppl 2006; (360): 546-50.
https://doi.org/10.1111/j.2042-3306.2006.tb05602.x
[14] Tessier C, Holcombe SJ, Derksen FJ, Berney C, Boruta D.
Effect of stylo-pharyngeus muscle dysfunction on
nasopharynxin exercising horses. Eq Vet J 2004; 36(4): 318-
23.
https://doi.org/10.2746/04251640448905 53
[15] Tessier C, Holcombe SJ, Stick JA, Derksen FJ, Boruta D.
Electromyographic activi ty of the stylopharyngeus muscle in
exercisi ng horses. Eq V et J 2005; 37(3): 232-5.
https://doi.org/10.2746/04251640545307 59
[16] Bertone JJ. Excessive drowsiness secondary to recumbent
sleep deprivation in two horses. Vet Clin N Am: Equine Pract
2006b; 22(1): 157-162.
https://doi.org/10.1016/j.cveq. 2005.12.020
[17] Bertone JJ. Sleep deprivation is not narcolepsy in horses. In
Proceedings 24th ACVIM Forum (Louisville) 2006; pp. 167-
169.
[18] Mathew IG. Sleep disorders ,seiz ures and epi lepsy in horses.
In Proceedings 23rd ACVIM Forum (Baltimore) 2005; pp.
144-146.
[19] Ahern T. Behavioural Changes in a Ten Year Old Gelding
that Presented with Palatal Instability, and Observations
Made following an Oral P alatopharyn goplasty. World J o f Vet
Sci 2018; (6): 38-41.
https://doi.org/10.12970/2310-0796.2018.06.08
[20] Ahern T. Sleep Attacks with Associated Sleep Terrors in a
Six Year Old Thoroughbred Gelding. World J of Vet Sci
2018; (6) : 19-22.
https://doi.org/10.12970/2310-0796.2018.06.03
[21] Allen KI, Franklin S. Characteristics of palatal instability in
Thoroughbred racehorses and their association with the
development of dorsal displac ement of the soft palat e.
Equine Vet J 2013; 45(4): 454-459.
https://doi.org/10.1111/evj.12004
[22] Allen KI, Franklin S. The effect of palatal dysfunction on
measur es of ventilation and gas exchange in Thoroughbred
racehorses during high intensity exercise. Equine Vet J
2013b; 45(3): 350-354.
https://doi.org/10.1111/j.2042-3306.2012.00627.x
[23] Barakzai SZ, Hawkes CS. Dorsal displacement of the soft
palate and pala tal instability. Equine Vet Edu 2010; 22(5):
253-264.
https://doi.org/10.1111/j.2042-3292.2010.00060.x
[24] Holcombe SJI, Derksen FJ, Stick JA, Robinson NE.
Pathophysiology of dorsal displacement of the soft palate in
horses. Equine Vet J Suppl 1999; (31): 45-48.
https://doi.org/10.1111/j.2042-3306.1999.tb05186.x
[25] Ducharme NG. The pharynx. In: Auer JA, Stick JA, Ed.
Equine Surgery. 3rd ed. St Louis: Saunders 2006; p. 552.
https://doi.org/10.1016/B1-41-600123-9/50045-0
[26] Ahern T. The Modified Or al Palatopharyngoplasty or
Modifie d Ahern Proc edure. World J of Vet Sci 2018; 6: 33-37.
https://doi.org/10.12970/2310-0796.2018.06.07
[27] Ahern TJ. Oral palatopharyngoplasty. J Equine Vet Sci 1992;
13(4): 18 5-188.
https://doi.org/10.1016/S0737-080 6(06)81000-2
[28] Mene ndez IM, Mancha DAI, Fitch G. Fourth Branchial arch
defects in full-siblings treated with a partial arytenoidectomy.
Equine Vet Educ 2011; 25(6): 274-277.
https://doi.org/10.1111/j.2042-3292.2011.00325.x
[29] Fjordbakk CT, Chalmers HJ, Holcombe SJ, Strand E. Res ults
of upper airway radiogr aphy and ultr asonography predict
dynamic l aryngeal collaps e in affec ted horses. Equine Vet J
2013; 45(6): 705-10.
https://doi.org/10.1111/evj.12066
[30] Garrett KS, Woodie JB, Embertson RM, Pease AP.
Diagnosis of laryngeal dysplasia in five horses using
magnet ic resonance imag ing and ultr asonography. Equine
Vet J 2009; 41(8): 766-71.
https://doi.org/10.2746/042516409X434080
Upper Oesophageal Sphincter Aplasia in Equids World Journal of Veterinary Science, 2021, Vol. 9 15
[31] Garrett KS. Adv ances in diagnostic imag ing of the larynx and
pharynx. Equine Vet Educ 2011; 24(1): 17-18.
https://doi.org/10.1111/j.2042-3292.2011.00269.x
[32] Pekarkova M, Kircher P, Konar M, Lang J, Tessier C.
Magnet ic resonanc e imaging of th e normal equine larynx and
pharynx. Vet. Radiology and Ultrasound 2009; 50(4): 392-7.
https://doi.org/10.1111/j.1740-8261.2009.01555.x
[33] Tulloch LK, Piercy RJ, Troester S, Caruthers R, Tast V,
Grimes L, Perkins JD. Use of Laryngeal Compute d
Tomography for Noninvasive Assessment of Laryngeal
Function in Horses with Recurrent Laryngeal Neuropathy.
Equine Vet J 2014; 46(S47): 17.
https://doi.org/10.1111/evj.12323_38
[34] Parente EJ, Martin BB, Tulleners EP, R oss MW. Dorsal
Displacement of the Soft Palate in 92 Horses During High-
Speed Treadmill Examination (1993–1998). Vet Surg 2002;
31(6): 50 7-512.
https://doi.org/10.1053/jvet.20 02.36009
[35] Lane JG, Bladon B, Littl e DR, Naylor JR, Franklin SH.
Dynamic obstructions of the equine upper respirat ory tract.
Part 1: observations during high-speed treadmill endoscopy
of 600 Thoroughbred racehorses. Equine Vet J 2006; 3 8(5):
393-399.
https://doi.org/10.2746/04251640677840 0583
[36] Franklin SH, Naylor JRJ, Lane JG. Videoendoscopic
evaluatio n of the upper respiratory tract in 93 sport horses
during exercise testing on a high-speed treadmiII. Equine vet
J 2006; 38(S36): 540-545.
https://doi.org/10.1111/j.2042-3306.2006.tb05601.x
[37] Smith LJ, Mair TS. Fourth branchial arch defect in a Welsh
section A pony mare. Equine Vet Educ 2009; 21(7): 364-66.
https://doi.org/10.2746/095777309X446586
[38] Motamedi KK, McClary AC, Amede e RG. Obstructiv e Sleep
Apnea: A Growing Problem. Ochsner J 2009; 9(3): 149-153.
Received on 15-01-2021 Accepted on 27-02-2021 Published on 03-03-2021
https://doi.org/10.12970/2310-0796.2021.09.03
© 2021 Tom Ahern; Licensee Synergy Publishers.
This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License
(http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in
any medium, provided the work is properly cited.
