Myasthenia Gravis

My dog's been diagnosed with a condition called Megaesophagus and is being treated for Aspiration Pneumonia.  I’ve just learned that the cause is Myasthenia Gravis, a disease I’ve never heard of that I can’t even pronounce.  Now what?

One day, I have a perfectly normal dog, and the next, there’s something terribly wrong.

Relax…. Breath… Ahhhh….

Okay, let’s start at the beginning.  Myasthenia Gravis (MG), pronounced (My-as-theen-ee-a Grav-us), comes from Greek and Latin words meaning grave muscle weakness.

It is a Neuromuscular Autoimmune disease.  Let’s break that down:

What is the neuromuscular system?
The nervous system is divided into the central nervous system (brain and spinal cord) and peripheral nervous system (also called neuromuscular system, composed of nerves and muscles).  The neuromuscular system consists of the nerves leaving the back of the brain to innervate muscles and glands of the head (cranial nerves), and peripheral nerves leaving the spinal cord to control in particular the muscles of the limbs.  The junction between the peripheral nerve and the muscles is called the neuromuscular junction. 
                            

 

A chemical messenger called acetylcholine (pronounced ah-See-tul-KO-leen) bridges this gap. This messenger is released from the end of the nerve, flows across the gap and fixes itself to a specific receptor (acetylcholine receptor) on the muscle. The acetylcholine attaches to the receptor (like a key fitting a lock) and triggers a signal, which causes the muscle to contract.

Autoimmune…

In Myasthenia Gravis, there is abnormal transmission of the message between the nerves and the muscles.  In the body of an MG dog there is a reduction of the number of receptor sites.  The reduction in the number of receptor sites is caused by an antibody that destroys or blocks the receptor site.  Antibodies are proteins that play an important role in the immune system.  They are normally directed at foreign proteins called antigens that attack the body.  Such foreign proteins include bacteria and viruses.   Antibodies help the body to protect itself from these foreign proteins.  For reasons not well understood, the immune system of a dog with MG makes antibodies against the receptor sites of the neuromuscular junction.  Abnormal antibodies can be measured in the blood of many dogs with MG.  The antibodies destroy the receptor sites more rapidly than the body can replace them.  Muscle weakness occurs when acetylcholine cannot activate enough receptor sites.

                                      



There are two types of Canine Myasthenia Gravis:      

Congenital Myasthenia Gravis

In this condition, the patient is born without normal neuromuscular junctions to striated muscles. There is no effective treatment.  Myasthenia Gravis has been described as a recessive genetic disease in Jack Russell Terriers, Springer Spaniels, and Smooth Fox Terriers.  The Miniature Dachshund gets a congenital form that actually resolves with age.

Acquired Myasthenia Gravis

This is a so-called autoimmune disease, meaning that the immune system is destroying neuromuscular junctions as if they were foreign invaders. What muscles are affected depend on which junctions have been destroyed.  Therapy centers on stopping this immune reaction and prolonging what acetylcholine activity is still present.  This is done with a combination of immunosuppressive agents and medication to inhibit acetylcholinesterase.

Acquired Myasthenia Gravis can be further divided into three categories:    

Group 1)  Mild or Focal MG – only one body part, usually the esophagus, is involved.

Group 2)  Moderate Generalized MG – appendicular  (limb) weakness with or without Megaesophagus.

Group 3)  Severe Generalized or Acute Fulminating – rapidly progressive and usually fatal.     




                  

MG affects the striated voluntary skeletal muscles of a dog.  Take a look at the illustration above; notice the heavy concentration of muscles in the neck area and hind quarters.  This is why 90% of dogs with MG also have Megaesophagus.  It is the reason why hind leg weakness is also a tell tale sign of MG.

Signs and Symptoms

  • Megaesophagus

  • Bark Change (usually high pitched)

  • Hindquarter weakness or limb weakness – Sudden urge to “sit down”. Weakness appears after exercise and condition improves after rest.

  • Blink Reflex (Palpebral reflex) – A reflex elicited by touching the eyelid and observing for a blink. This response fatigues or is absent in animals with MG.  (watch how to test for Palpebral Reflex)                

http://www.youtube.com/watch?v=4_zdjL51qoU      

  • Walking with stilted rear legs, quivering or shaking rear legs, running sideways, unable to jump or climb stairs. (ex. of MG rear weakness)

http://www.youtube.com/watch?v=ZBR686banRc

 

  • Drooping lower lip – sudden increase in drool due to weakness in lower lip

  • Drooping tail

  • Trouble controlling urine stream or holding squat while defecating

  • Lethargy

  • Excessive Drool
  • Moaning noise primarily when lying down

 

Symptoms can vary from dog to dog.  A dog may have one symptom or many.

Diagnosis and Treatment

If Congenital Myasthenia Gravis is suspected, it is recommended that your veterinarian contact Dr. Diane Shelton directly through the website Comparative Neuromuscular Laboratory @ http://vetneuromuscular.ucsd.edu/index.html  A muscle biopsy will need to be sent.  Congenital MG cannot be detected by blood test.

For Acquired Myasthenia Gravis, a blood test can be done to check for antibodies against acetylcholine receptors.  It is called an AChR test.  This blood test is able to detect 98% of pets with myasthenia gravis.  When antibodies drop to less than 0.6 nmol/L, clinical signs generally resolve.

Serum should be collected before corticosteroid therapy is initiated because immunosuppressive doses of corticosteroids for longer than 7-10 days lower antibody concentrations.  

Seronegative myasthenia occurs in approximately 2% of dogs. The percentage of positive tests in the focal form of MG may be slightly less, but currently there is no other way to diagnose the form of MG.  If the vet strongly suspects MG and antibody test is negative, the positive clinical findings probably should take precedence over negative confirmatory test and a diagnosis of possible MG should be made and treatment should be started.  If clinical signs were recent in onset, retesting in 1-2 weeks may confirm the diagnosis.

The test is available through one lab, Comparative Neuromuscular Lab at the University of California, San Diego, in LaJolla, CA.  The test takes between 5-7 business days to perform after it is received.

 

Tensilon Test

This test involves giving an injection of edrophonium chloride (brand name Tensilon) intravenously to a patient suspected of having myasthenia gravis.  Edrophonium chloride is a short-acting anticholinesterase. This allows acetylcholine to accumulate in the neuromuscular junction, strengthening the message from nerve to muscle.  A dramatic increase in muscle strength following the IV injection should give a presumptive diagnosis of acquired MG while waiting for the results of the AChR antibody titer test.  Treatment could be initiated based on the results of the dramatic positive test. Unfortunately, not all dogs are responsive to Tensilon, and dogs with other neuromuscular diseases may show a subjective positive response.

Watch Buddy’s positive Tensilon test:

http://www.youtube.com/watch?v=k7YX9kuWrxA

Watch Lily’s Positive Tensilon test

http://www.youtube.com/playlist?list=PL177795CB4819FAD7

Focal MG Pre and Post Positive Tensilon Test

http://www.youtube.com/watch?v=-13EIGGP4bk

Chest Radiographs (X-Rays)

A chest radiograph set should be taken to check for thymoma. A thymoma is a tumor on the thymus gland. Surgery to remove the tumor is sometimes recommended for patients who have thymic masses so it is important to identify these patients. Thymoma may be associated with an acute, fulminating MG.  Thymoma is much more prevalent in cats. In dogs, only around 3-4% of patients will fit this category.

     

   Thymoma

      

Megaesophagus

Another reason to take a chest radiograph is to look for megaesophagus and aspiration pneumonia.

 

Treatment:

Anticholinesterases – first line of defense

Pyridostigmine  is the typical medication used to prolong the action of acetylcholine.  Neostigmine  is also sometimes used although Pyridostigmine is preferred for fewer side effects.  By inactivating acetylcholinesterase, the receptors that have not been destroyed by the immune system can bind acetylcholine longer.   It is typically given orally 2 to 3 times daily with food.  The syrup form should be diluted with equal parts water.  It comes in syrup, tablet and time span forms.  Close supervision with your veterinarian is advised in regards to dosing these drugs.  If patient exhibits signs of worsening weakness, vomiting, cramping, diarrhea, tearing or drooling the vet should be notified immediately.  Many canine patients will require no further treatment beyond this medication.

Sometimes corticosteroids, immune-suppression drugs, like prednisone, azathioprine, mycophenolate mofetil, and cyclosporine may be used if clinical signs of MG are not completely relieved with anticholinesterase drugs. Prednisone is a synthetic drug taken by mouth that resembles natural hormones produced by the cortex of adrenal glands.  The body depends on these hormones, called corticosteroids, during stress. Prednisone has a great many potential undesirable effects in dogs including suppression of adrenal gland functions, marked muscle weakness, and muscle atrophy.  

Unique to MG is the possibility of increasing weakness during the first two weeks of prednisone therapy.  This necessitates close medical supervision when prednisone is instituted, either on an outpatient or in-hospital basis. Azathioprine also may be of use in canine MG but side-effects require frequent monitoring of blood counts to detect rapid drops in the number of white and red cells in the blood, and periodic liver function tests to detect potential toxicity to the liver.

Medications can be complicated and must be monitored closely by you and your veterinary care professional.

Plasmapheresis or Plasma Exchange is a treatment in which plasma (containing pathological antibodies) is removed and exchanged with donor plasma. This is a treatment used often in human MG. Dogs may have 3-5 treatments and it requires hospital stay. It can be done in some university veterinary hospitals and larger vet specialty hospitals. It is quite costly if you do not have pet insurance that will cover it.The advantages are dogs can became ambulatory within 3 days of starting treatment with subsequent resolution of regurgitation and megaesophagus.

Remission

Here’s the really, really good news! Unlike humans, canines can actually go through spontaneous remission sometimes as early as four months after first clinical signs. The average time for remission is 6-8 months, with some dogs taking over a year to go into remission.  Many times the megaesophagus resolves as well.

Prognosis

Prognosis is good!  As long as the symptoms of megaesophagus are well managed to lessen the danger of aspiration pneumonia, your pup has a good chance of kicking this thing!

Follow Up and Tips

  • Periodic chest x-rays and AChR antibody titer test are suggested to monitor the disease until remission is achieved.  Many Neurologist DVMs suggest every 3 months. 

  • Wean off of meds slowly with your vets guidance.  Let your veterinarian be the toxicologist with the cocktail of drugs.

  • Avoid stress whenever possible.  Excessive heat or cold, and overexertion can exacerbate symptoms.

  • Do not vaccinate.  Please discuss this with your veterinarian.

  • Trust your gut.  If you see something that doesn’t look right, contact your vet and get in for an exam.

  • Stay vigil.  Relapses do occur. Sometimes the same muscle groups are affected, and sometimes it can look completely different.

  • Stay in close communication with your vet, especially in the early days. Daily check ins are really important, whether it be by phone or email with pictures and/or videos.

  • If your vet is not knowledgeable about the disease, and does not want to consult with specialist to help your dog, find another.  Look for a Neurologist DVM.

  • Keep a daily log on what meds are administered and when. Record any reaction your pup may have; progress or set backs.

  • This site is for general information and support, and does not replace a visit with your vet.  Your vet will have the most accurate information and hands on knowledge about your pup. 

  • Remember this…as bad as it may look, MG is a painless disease.  There is not pain associated with the weakness they are experiencing.

Take heart, you are not alone in this. We are here to help you through it!

  • Brix
  • Annika

MG Pamphlet to SHARE with your vet and others!

121 thoughts on “Myasthenia Gravis

  1. My dog Lillie is a Boxer/Shepard mix (we think – I picked her up from a shelter when she was 1 years old and that’s what they believed she was). She will be turning 3 years old this month. Within the last month my dog has been experiencing slow but increasing muscle atrophy in her hind legs and hips. With her atrophy has come weakness, of course, and so much so that within the last few days she has to sit every time she stands or when she does stand she is constantly “dancing” with her back legs while they are shaking. She is unable to jump on the couch or anything anymore. The vet completed a full blood panel, checked their thyroid and kidney function which all came back normal. Her physical exam showed full range of motion (she was uncomfortable you could tell) with nothing seeming out of sort. She is eating and drinking plenty. The MG test will be taken this given Monday. Are these signs all leading to MG? Should I expect ME? In the meantime, she is appearing nauseous (licking her lips, can’t sit still. Is there anything I can do?

    1. And what scares me with these comments about the vaccines… I JUST started Frontline Gold for dogs about a month ago. She weights 48 pounds and the vet prescribed me 45-88 lbs Frontline.

      1. Frontline Gold is perfectly safe to use with a dog with MG. There is no correlation to flea and tick prevention or heartworm preventatives. It is a good idea to keep on that since you wouldn’t want your dog to have either of those disease (tick bore disease or heart worm) onto of everything else her immune system is fighting. I’m not a vet but that sounds like the proper dose for a dog that weighs 48 pounds. Best of luck Morgan!

    2. Hi Morgan,
      Our dog presented similarly to your dog. He did not have ME and he never got it. Most dogs do get megaesophagus but there are about 10% that do not. A dogs esophagus is made up of all striated muscles. MG attacks that muscle group. But it is called the snowflake disease for a reason. Their symptoms can really vary from dog to dog. Good luck with Lillie. You are doing the right thing by having her tested. The could also ask your vet to do a tensilon test on her as well. If she reacts positively to it, it gives you a good idea that may be what it is. Some vet will simply start the dog on mestinon if they strongly suspect that is what it is. The drug works pretty fast and if she has it you would probably see results with in the first 24-48 hours.

  2. My dog was diagnosed with ME just a few days ago. Today he started having weakness in his legs. My vet told me that MG is so rare that if he were to have it I should just put him down. I’m devastated right now and don’t know what to do. I don’t feel I should second guess my vet but I don’t want to give up on him either. It’s all so overwhelming.

    1. Hi Lori,
      My advice would be to either try and educate your vet or find a new one. Those are classic signs of acquired MG. Many times the ME comes on first, followed by the hind leg weakness. All dogs that are diagnosed with ME (except if they are born with it) should be tested for underlying diseases. Those would include – Myasthenia Gravis, hypothyroidism and Addison disease. There are many causes of ME but certainly MG is not rare if your dog suddenly comes down ME. ME is a symptom of MG 90% of the time. Certainly push for testing!

  3. Both of my wiener dogs at different times were shaky and had weak hind legs.One of my dogs could not jump on the couch,could not climb stairs and would lay under the bed shaking.I thought maybe she had really bad arthritis or a bad back injury.I gave her calcium pills in wet cat food and she got better for a little while.so later I gave my dog a calcium pill in meat and my dog got worse as the days went by.Every day I gave my dog a calcium pills and she didn’t get better.It later dawned on me that maybe the wet cat food is what helped the first time.I gave my dog wet cat food every day for a few days and my dog improved immediately back to normal.Later when my other dog got the same type of condition,I gave her wet cat food and it worked for her and she went back to normal…Sharing this story because I believe it will help a lot of dogs.

    1. Hi Phil,
      I guess it could have been some deficiency in their diet. It is usually frowned upon to feed your dog a canned cat food for a long period of time. Dogs who have a steady diet of cat food are more apt to put on weight, and can have bouts of diarrhea and vomiting because of higher protein and fat levels in cat food. One critically essential amino acid cats need is taurine, which is added to their food. Dogs produce it on their own, so it’s not included in dog food. Glad she is feeling better now.

  4. Hi we have a 12 year old schnauzer who has recently been diagnosed with MG and megaoesophagus. He was only started on pyridostigmine 3 days ago but keeps regurgitating and coughing. Went to the vets and they have said very poor prognosis and consider letting him go. Would appreciate anyone’s thoughts and recommendations.

    1. Hi Anna,
      Managing the megaesophagus is very important with MG. Along with the pyridostigmine sometimes an acid reducer is also given. This sometimes helps with the reflux they are experiencing. Be sure to feed your pup in an upright position and have him remain upright for a period of time (between 15-20 minutes) some need less time, some more time. This allows gravity to do it’s job to move the food to the stomach. Pat his sides while he is upright to encourage him to burp. This will release air that may be trapped. With your vets guidance you may need to adjust the dose of the pyridostigmine until you see some relief on his symptoms. The first few weeks are the hardest with myasthenia gravis. There tends to be many med adjustments. Sometimes prednisone is added as well to help tap down the immune system. Best of luck. I hope your he makes it through this tough patch.

  5. Our 11 yr old Golden died this morning. 6 days ago he suddenly was unable to use his hind legs. I took him to our vet who examined him and found nothing wrong. Two days later I again took him in. Xrays showed nothing which was good news. He was put on predizone and more pain pills. This was Monday. On Tues.he started retching….not vomiting…..coughing up phlegm and drooling. He was still unable to use his hind legs. We had to sling his back legs to get him outside etc. Because the retching got so bad on Thurs. we took him to Blue Pearl vets. His bloodwork was pretty good but the vet said she though it might be MG with megaesophagus and that there were meds that could help. She wanted a blood test taken the next day (Fri) and we were given the choice of leaving him there or taking him home to return the next morning. We arrived home around 10 P.M. By 1A.M. his retching was so horrible that he was unable to lay his head down. We took him back to Blue Pearl thinking that they would be able to keep him comfortable. The vet said she would phone us before leaving her shift around 6:30A.M. The call came telling us that Buckinghamm’s breathing had become quite bad and they felt that he had aspirated . I told her we would be right there (25 min.away) She said that she would have to intubate. When we arrived he was sedated and intubated. When he heard our voices his breathing became faster so I felt he knew we were there. It seemed the only option at that time was to put him down. So now, from what I have just read, there may have been something that could have been done. His age may have been a problem but he was really healthy 6 days ago. I wonder if his regular vets were more aware of this disease and it was caught earlier he might have had a chance. I’m not blaming anyone other than myself for not taking him to a large university right from the start. I am going to tell my vets about this web site so hopefully the next pup will stand a chance. Our hearts are broken to think we could have spared this wonderful dog the agony he went through.

    1. Oh Margot I am so sorry. It’s really difficult to say if there was anything different that could have been done. There is that form of MG called fulminating MG that comes on quickly and is usually fatal. This could be what was going on. Try not to second guess your decision. You obviously loved your sweet boy so much to seek out the care that he needed. Myasthenia gravis is very difficult to diagnosis since most vets feel it is so rare. And perhaps it is. We see so much of it in group we forget how rare it truly is. Peace to you and your family. Try to focus on those happy memories that I’m sure you have of your precious boy. He would want you to be happy. <3

  6. Hi my vet thinks that my dog, Norrington has Myasthenia Gravis. They have done the blood test amd have started hom on medication. It is early days but no improvement yet. It is heart breaking to see him just laying on his mat when he was an active dog.

    1. Hi Sally,
      It does take some tweaking of the meds to get adjusted. Remember, there is no pain with the MG. It looks terrible and they are very lethargic and weak. Sometimes a low dose of prednisone is prescribed to help tap down the immune system to get them going. Hang in there. Things will get better. <3

  7. Hi, my dog Tango got diagnosed with ME about two months ago after being sick for a year. Yesterday we went to the vet because something was wrong with his leg, and all his symptoms point to MG. We sent for the blood test and are waiting on the results but are treating him with a low dosis of the medicine. He is doing really well on the medicine. The only thing is that when his dosage is wearing off his front leg starts giving him issues. We are doing about 1/6 of what could be his dossage until further confirmation of his condition. I was just wondering if any of you has seen this. It has been really good reading about it here, it kind of gave me hope.

    1. Hi Carolina,
      That’s really good news that the medicine is working. More than likely that blood test is going to come back positive for MG since you are seeing a positive response to the meds. The drug does lose it’s effectiveness after so many hours. How often are you giving the pyridostimine (mestinon), every 8 hours or every 12 hours? Your vet may want to increase your dosage or have you give it every 8 hours instead of every 12 hours. Many dogs do go into remission from the disease. Sometimes the ME resolves as well. Keep looking up!

  8. My seven year old schnauzer has been recently diagnosed with myasthenia gravis and megaesophagus. It has all happened very quickly within the last month, shortly after he received a rabies shot. I don’t know if the shot triggered this or not. I have read online that flea and tick medication can also be bad for this disease, my vet recommends that I still treat him but I am worried that it could make him worse. I would like to know if other people have had any problems with flea and tick medication or is it generally pretty safe? Also would maybe a topical medication like revolution be better than ingesting a treatment like heart guard? Any help would be appreciated, thank you.

    1. Hi Kristi,
      My dog also had MG and our neurologist from the University of Penn recommended that we continue with flea and tick medication and also heart worm. We used Heartgard and Frontline Plus with no issues ever. His MG went into remission. No vaccinations however are to be given. There may be a connection between vaccinations and MG, just nothing has been proven. Our dog also acquired MG after vaccinations. Keep looking up!

    2. Hello Kristi,
      I am going through this with my boxer. Not vaccine related. We thought she had a back injury 3 weeks ago. Then ME symptoms started and it looks more like MG. We are in the process of confirming the diagnosis. I have never used the monthly flea and tick treatments on our dogs. We have white boxers and white dogs tend to react badly to the topical prevention formulas. I use Wondercide. It is made from cedar oil. Non toxic to pets and humans. http://www.wondercide.com/
      Good luck with your baby.

  9. I am currently fostering a dog that has MG and takes medication 2 x day I only have him 2 weeks but he is regurgitating constantly and then tries to eat it and the shelter person is saying he could go into remission and led me to believe the concern was his back leg muscles but he doesn’t seem to be able to eat without vomiting

    1. Hi Christina,
      The biggest problem with acquired myasthenia gravis isn’t the back legs, it is megaesophagus. Apart from giving the mestinon for the MG, managing the megaesophagus is paramount in getting this dog through this. Yes they can go into remission. What takes their life more so than anything else is aspiration pneumonia and the complication of it. When a dog regurgitates his food, water or saliva there is a chance that he can aspirate that substance into his lungs causing an infection. To guard against that, the dog needs to be feed upright either in a chair or some other way and kept upright until the food reaches the stomach. He will need to be fed a soft diet, no hard kibble. Check the recipe tab for examples. Water can be an issue. You may need to add enough water into his food by blending it to keep him hydrated. Many ME dogs can not tolerate straight water. This can be managed and in 6 months time this dog could resume a normal life. There is a lot of hope with MG. Join the facebook groups for more discussion and ideas that will help you out. Click on the red ribbons at the bottom of the home page. Best of luck to you and thank you for loving a special needs pup!

  10. My dog Kenny is being treated for ME and MG. Current Meds are, Pyridostigmine BR 60mg twice a day, Metoclopramide 15mg twice a day. Prednisone, and Pepcid. We are currently weaning him off prednisone and Pepcid. He was on 30mg a day of prednisone when he first started and was doing great so the Vet suggested we start weaning him off it. We went down to 20mg a day for 2 weeks and he did great. We are currently on the second week of 20mg every other day. The first week was fine. The second week hasn’t been. He does good for The first day and a half after his prednisone and then his energy decreases, he sleeps longer, drools more, and eats way slower. When I give him his Meds, his tongue seems to be much weaker. When I give him his prednisone for that day he gets much better after a few hours. Is this normal? Any help would be wonderful!

    1. Hi Lisa,
      You will find that the meds are a true balancing act. Under the guidance of your vet, I would talk to him about either increasing the Pyridostigmine while decreasing the prednisone or cutting back slower on the prednisone. I don’t know how far along you are with the progression of the MG. Generally it is advised to run a titer every 3 months however prednisone use can lower the test results. Best of luck with your pup!

Leave a Reply

Your email address will not be published. Required fields are marked *