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Myasthenia Gravis in Dogs
Myasthenia Gravis
Myasthenia Gravis and other possible problems
Myasthenia Gravis
Myasthenia Gravis in young Mastiff possible
Test for Myasthenia Gravis
also see neurological problems
also see Thyroid problems
also see megaesophagus
Myasthenia gravis is a neuromuscular disease in which weakness is the primary sign. This disease is caused by an inability of the certain nerve receptors (nicotinic acetylcholine receptors (AChRs) to function properly. This prevents the stimulus for muscles to contract which leads to the weak appearance. This disease occurs congenitally in some dog breeds. Jack Russell terriers, springer spaniels and smooth fox terriers are affected. It can also occur as an acquired problem in older dogs. In this case, it is thought to be an immune mediated disease. In older dogs, the first sign of problems may be megaesophagus -- enlargement of the esophagus due to the muscular weakness, leading to problems swallowing. This can cause regurgitation and lead to inhalation pneumonia.
Myasthenia gravis can be very variable in the way it looks. Only a few muscle groups may be affected or the dog may be nearly immobile. A dog can be almost normal after a rest and then lose strength very rapidly when it exercises at all.
Whenever megaesophagus is diagnosed, myasthenia gravis (MG) should be suspected. Conversely, whenever myasthenia gravis is diagnosed, chest X-rays should be done to evaluate the esophagus, in case megaesophagus is present.
MG can be presumptively diagnosed by a rapid response to injection of edrophonium hydrochloride (Tensilon). Dogs usually show an immediate improvement in muscle strength that is of short duration. Specific lab tests for this disease are available to confirm the diagnosis.
Dogs that acquire MG later in life usually have a fairly good prognosis with treatment. It is important to prevent aspiration pneumonia, so dogs should be fed from elevated food bowls and encouraged to remain standing for 10 minutes or so after eating. Anticholinesteras medications are very helpful. Pyridostigmine bromide (Mestinon syrup) is the most commonly used medication. If it is not effective, injections of neostigmine (Prostigmin) will sometimes work. In severe cases, corticosteroids may be necessary. It is very important to make sure that there are no other illnesses and no aspiration pneumonia signs prior to using corticosteroids.
Dogs can be maintained well for a long time with this disease. The more attention paid to prevention of aspiration pneumonia, the better the long term prognosis. In addition, many other medications interfere with the actions of the anticholinesterase drugs, so careful thought must be given to the choice of medications to treat other problems in dogs affected with myasthenia gravis.
A number of dogs with acquired MG will have remissions from the disease. Therefore, it is very important to monitor the antibodies to anticholinesterase receptors prior to treatment and at regular intervals during treatment. Recurrences of the disease after remission can occur, so vigilance is required throughout the lifespan of affected dogs.
Mike Richards, DVM
Myasthenia gravis and other possible problems
Question: Dear Dr. Richards: About three -four weeks ago, our ten year old
female/spayed Golden Retriever became extremely upset during the middle of
the night, jumping on and off the bed, trembling, panting heavily.
Eventually, after several hours, she calmed back down and went to sleep.
Subsequently, we started noticing symptoms, including that she was not
blinking her left eye and the left eye seemed larger than the right. She
also began having difficulty eating and drinking from her bowls and was
panting excessively. Over the course of the next couple of weeks, I had to
hand feed her canned dog food and she refused to eat any hard food or
biscuits. I was also having to elevate her water dish up to her face where
she still had a lot of difficulty lapping up the water. She paced alot
inside with her tail between her legs and appeared to have difficulty getting
comfortable, but for a time, seemed to be happy and wagging her tail out on
walks. Her bark became extremely hoarse and she seemed to have some
difficulty with the control over her mouth and tongue. Last week, she became
extremely weak to the point that she was tipping over and we had to help lift
her hind end up and down the two stairs to get out of the house for her
walks. During this time, we saw our vet several times who thought that she
was suffering from a brain tumor. All blood work and x-rays came back
normal, however. We decided to wait a little bit to see if she would improve
to determine whether she was suffering from a vestibular syndrome since we
could not afford to have an MRI done at a cost of over $1000. Her symptoms,
however, worsened to the point where she could not walk at all due to rear
end weakness and had virtually stopped drinking and eating. As a result, we
were forced to euthanize her this week. Since we are likely to get another
Golden (although no other dog will replace our beloved, Teddy) I was
wondering if you could answer these questions for my future reference: 1)
Was it possible that she had something other than a brain tumor given the
negative blood work and x-rays and, if so, were there other diagnostic
studies other than an MRI that we should have looked into? 2) How pervasive
are brain tumors in Golden Retrievers? (I subsequently heard from several
other people that their Goldens also died from brain tumors; and 3) Are these
tumors usually genetic, i.e., where a reputable breeder should know if there
is a family history of this problem? Thank you very much. I spent a lot of
time reading your site during this recent crisis and it was a big help.
Sincerely, JulieAnswer: Julie-
There are two disorders that I would have considered with the clinical signs that Teddy had.
The first is myasthenia gravis. This disease is characterized by neuromuscular weakness and is a
close fit for the symptoms that you observed. Early in myasthenia gravis there is a tendency for
subtle to fairly noticeable weakness of one or more legs. When dogs with this disease are tired they
may have drooping of the facial muscles and it is not uncommon for there to be oculomotor
problems, as well. Voice changes are also not uncommon with myasthenia gravis. This is an acquired
immune mediated disorder most of the time when it occurs in older dogs. It is more common in large
breed dogs, with German shepherds supposedly being the most commonly affected breed. In our
practice, though, golden retrievers seem to outnumber the other breeds with this problem. This may
just be a local variation in our area, however. Testing for this disease can be done tentatively by
administration of a medication, edrophonium chloride (Tensilon Rx) and watching for nearly
immediate improvement in clinical signs which then rapidly return as the medication wears off after
five to ten minutes. If this testing seems to indicate that the disease is present, it can be confirmed
through serum testing and sometimes through muscle biopsy. Myasthenia gravis may respond
reasonably well to medical treatment, based on the information in the literature, but this is definitely
not always the case.The other condition that I thought of, but think is much less likely, is severe hypothyroidism. I
suspect that this was probably tested for in the lab work that was done, though. Hypothyroidism has
been linked with facial paralysis, laryngeal paralysis, muscular weakness and a number of other
signs. When hypothyroidism becomes severe, it sometimes causes a "tragic" expression on a dog's
face due to facial edema.Brain tumors are supposed to represent about 1 to 2% of the natural causes of death in dogs, so that
is between 1 in 100 and 1 in 50 dogs. There is a lot of variability in the suspected heritability of
different brain tumors and in many (most?) cases it is not known with certainty if the tumors are
inherited. Without a post mortem examination which identified a brain tumor, it is hard to say if one
was really present. I think that many instances of suspected brain tumors might turn out to be other
things if post mortem examinations were done -- and that there would also be a lot of cases in which
a tumor was not diagnosed when one was actually present.I think that golden retrievers are more prone to lymphomas than other dog breeds even though I can
not recall seeing proof of this in the veterinary literature. I would ask a breeder whether this tumor
had been a problem in the breed line, though. Hemangiosarcomas may also be more common in this
breed than in many other breeds but that is also just a personal observation.It is important to understand that actually seeing and examining a pet allows some possible diagnoses
to be ruled out even though they sound like they may be present based on clinical signs. Your vet
had the opportunity to make this kind of an examination, so even though myasthenia gravis seems
very possible based on the signs you describe, your vet may have good reasons for believing it was
not present.Mike Richards, DVM
5/22/2001
Question: Hello Dr. Mike,
My dog Jake 100 lb. Shepherd X Husky age 8 has been diagnosed with
Myasthenia Gravis. He was on Mestinon for about 5 weeks and it seems to be in
remission! (whew) But the poor guy has some sort of bacterial rash from
swimming in the lake all over his body, he's lost some fur, has large flakes,
rash, redness, itching etc. Today while brushing his belly I noticed a thick
yellow discharge from his penis! The Vet tried in this order 1. Amoxiclian 2.
Medicated bathes 3.Prednizone 4. Skin and Coat liquid supplement 5. Wysong
Anergen
What more can we do???Thanks in advance!
Lisa
PS. I love your site!!!
Answer: Lisa-
The discharge from the prepuce is probably normal. There is a thick
exudate, referred to as smegma, which is thick yellow to yellow-green in
color and is normal. For some reason, it may seem to suddenly accumulate
in larger quantities in some dogs. This may also relate some to the overall
skin condition.The skin rash might be a drug reaction. Some patients are reported to be
sensitive to pyridostigmine bromide (Mestinon Rx) but I haven't actually
seen skin rash listed as a side effect, just cautions about using this
medication in patients who are sensitive to it. Still, if this rash started
after you started using pyridostigmine, it would definitely be worth
considering. It may be possible to withdraw pyridostigmine in the future,
which would be helpful if it is the cause of problems. It is acceptable to
use pyridostigmine in conjunction with corticosteroids or azathioprine
(Imuran Rx), which are immunosuppressive medications and might help with a
drug reaction. Of course, it is possible that this is a primary skin
infection and that antibiotics or anti-fungal medications (for yeast
infections) may be necessary to control it. In that case, immunosuppressive
medications would not be advisable. Since it is hard to be certain a drug
reaction is occurring we often try the antibiotics first and other
medications only if they aren't helpful. A skin biopsy can be helpful in
determining what is happening and in complicated cases like yours, we try
to do them early on since the trial and error approach can take some time.
Another immunosuppressive medication that has sometimes been helpful in
combination with Mestinon is mycophenolate (Cellcept Rx). This is a
relatively expensive choice, though.Hope that this helps some.
Mike Richards, DVM
11/21/2000
Myasthenia gravis in young Mastiff possible
Question: Dear Dr Mike,
Last Saturday (4/8), it became extremely difficult for our male Mastiff (11 months old) to walk -- even with
assistance. His condition developed suddenly and without any trauma. We took him to an emergency
veterinary hospital; however, the Vet was unable to diagnosis the problem. Vital signs, blood work, and
x-rays all appeared normal. He does not seem to be in any pain. Occasionally, he would try to get up, but
only collapsed. His condition remains about the same today, almost a week later.He saw our regular Vet on Monday, 4/10. After examining him, our Vet placed him on Primor, and referred
him to a Internal Medicine specialist.He was seen by the IM Specialist on Tuesday, 4/11. The specialist performed a spinal tap and additional
test of the serum. Spinal fluid was normal. Serum test ruled out tick borne diseases. Although the
dystemper test was negative, the specialist cautioned that this does not rule dystemper out. We are still
waiting for the results of the test for NEOSPIRA CANINUM. Since his condition was not improving, the
Specialist recommended that our Vet change his prescription from Primor to Clindamycin (750mg 2xDay).
This change took place on 4/13.He seemed to perk up a little last night (4/13), but began vomiting today (Fri 4/14). Our Vet is treating him
to prevent the vomiting.Would appreciate any advise, or comments.
Sincerely, Bruce
Answer: Bruce-
My first thought on reading your note was that your mastiff might have myasthenia gravis. There
is a pretty high correlation between myasthenia gravis and megaesophagus in dogs, which is
commonly associated with vomiting and the weakness would be typical of this. There can be
acute onsets of this disease. There is a serum test for myasthenia gravis and a test using
administration of Tensilon (Rx), which usually causes rapid, but brief, improvement in clinical
signs.Polyradiculoneuritis seems possible, too. This is paralysis that usually starts in the rear legs and
then progressively worsens. It is similar to Guillain-Barre syndrome in humans. I don't know
how to definitively diagnose this condition but a veterinary neurologist may be able to. Tick
paralysis and acute idiopathic polyneuropathy are similar problems that might be present.The only other things I can think of, offhand, are heart problems, such as Cardiomyopathy, and
hypoadrenocorticism. Usually the onset of signs is much slower with cardiomyopathy and the
persistence of signs much less chronic with hypoadrenocorticism, though.I would worry the most about myasthenia gravis since early treatment may make it possible to
avoid severe complications associated with megaesophagus development. It is likely that your
vet and/or the specialist have considered this disease but it wouldn't hurt to ask about it.Mike Richards, DVM
4/18/2000
Q: Dear Dr. Richards.....
An entire online Mastiff list has been trying to help us because we are so
desperate. Our 13 month old Mastiff puppy has had symptoms of collapsing
and seizure-like episodes after exercise. He has always been exercise
intolerant.
We have been to 5 vets, two Internal Med specialists and a cardiologist.
The last specialist mentioned a list of possible more tests to run since we keep
coming up emptyhanded......and the test for Myasthenia Gravis was one of
them.
I had no idea what this was so I came home and asked my mailing list. They
directed me to several websites including yours and the symptoms listed
fit my Mason's symptoms to a TEE!!!!
Can you tell me what I need to do to find out for sure if he has this??? I
heard it's some kind of blood screening, but I want to be exactly sure
what to do so that we leave no stone unturned. I hope you can help me! Thank
you!!!
Regards
KristenA: Kristen
The test for myasthenia gravis is done on serum. It must be sent chilled by
overnight mail so the arrangements have to made in advance and the sample
sent on a day when next day delivery is available. Dr. Diane Shelton is the
only person I know running the test. Her address is:Diane Shelton
UCSD School of Medicine
Basic Science Building Room B200
La Jolla, CA 92093-0614
619-534-1537It would be best to have your vet contact her to make any arrangements so
that there are no mix-ups in the communications. Please don't post her
address on a mailing list or bulletin board unless she says it is OK after
contacting her.Good luck with this.
Mike Richards, DVM
Last edited 01/30/05
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