Does anyone know about pain nerves in the esophagus?
 
I am wondering if the throats of members of carnivora are less sensitive
to pain than those of other animals, and if this might be one reason that
something like MegaE takes off as well as it does without early symptoms
in them.  Looking at Megaesophagus in the humans I notice that the
symptoms appear to show up much earlier with painful swallowing and
dysphagia.  In looking it up humans' causes appear to be neurological
diseases like Chagas and some other neural pathologies, or due repeated
stretching at areas with preexisting damage to the esophagus, and
POSSIBLY rarely as a congenital malformation.  (There are known dog
breeds with a congenital genetic aspects but what I have read so far
does not mention that in relation to anything else and says that it is
postulated but debatable.  Two special lab strains of rodents get it
spontaneously.)
 
http://www.critterchat.net/mega.htm#ref1
which is a comfy read in relation to dogs writes
>The increased incidence in these breeds is speculated to involve delayed
>maturation of the nerve plexus innervating the esophagus and lower
>esophageal sphincter.  These dogs often gradually acquire normal
>esophageal peristalsis and control of the lower esophageal sphincter over
>a period of a few weeks to two months2.  There is also a predisposition
>in certain canine breeds to develop megaesophagus secondary to patent
>right aortic arch2.  and In humans, the majority of megaesophagus cases
>are secondary to achalasia.  [Achalasia is the inability of a hollow
>organ to relax.]  People diagnosed with achalasia- induced megaesophagus
>range in age from 25 to 60 years1.  In achalasia-induced megaesophagus,
>there is an insufficient or uncoordinated relaxation of the lower
>esophageal sphincter and decreased peristalsis in the lower esophagus.
>The achalasia can be due either to muscular or neurologic abnormalities1.
>The neural component is considered to be more commonly involved1.  Other
>less common causes of megaesophagus in people include systemic disease,
>anatomic anomalies, myasthenia gravis, stroke, amyloidosis,
>hypothyroidism, vagal afferent dysfunction, Trypanosoma cruzi
>infections, and foreign body obstruction of the esophagus
 
(BTW, aspiration pneumonia appears to be common in any species with
this disorder.)
 
The reason I was wondering is because I had to have some tongue surgery
yesterday -- larger but far less painful and quicker starting to heal
than I was told to expect so, yes, you can joke about it with me off-line
should you so desire -- but the half dozen stitches rapidly tore out,
especially with swallowing, and I found that swallowing new stitches is
actually quite painful for the throat -- at least for my throat (and I
am someone whose med file includes "under reports pain" in bold red magic
marker).
 
Yet, ferrets, dogs, and cats and their wild relatives regularly swallow
far scratchier things without complaint and sometimes with relish, and
some love to try to eat string, fabric, or even dental floss.  They also
bolt food more, and seem to think little of bringing it up for more
chewing when needed.
 
So, I am wondering if perhaps members of Carnivora might at times
repeatedly injure the esophagus without feeling it much -- setting the
stage, and if they perhaps usually don't feel the beginnings of MegaE
from repeated injury because they might have a reduction in pain
perception in the esophagus -- basically that the sorts of things they
are inclined to eat might be what set them up for the condition, but do
note these essential points:
 
>Canines and rodents have striated muscle throughout the length of the
>esophagus, while in humans the proximal esophagus has striated muscle
>which gradually changes to smooth muscle in the lower esophagus5,6.
>In addition, a reproducible animal model of achalasia- induced
>megaesophagus has not been produced.
>
>...Some forms of megaesophagus respond to isosorbide dinitrate and
>calcium channel blockers treatment, physically by pneumatic dilatation,
>or by surgical myotomy of the lower esophageal sphincter.  In most
>cases, if there is an underlying degenerative neural lesion or other
>physiologic abnormality in the esophagus, the treatment is primarily
>for temporary amelioration of symptoms1.
 
And, yes, I realize that I am just hypothesizing here, so it is grain of
salt time, just as with any unproven thing that is postulated by anyone
anytime.
 
-- Sukie (not a vet)
Ferret Health List co-moderator
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replacing
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[Posted in FML issue 5036]