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!

163 thoughts on “Myasthenia Gravis

  1. I have an Irish wolfhound Morgana that we rescued as company for Galahad my other Wolfie just before xmas. She is six years old. She has always drooled a lot, not been as graceful or more awkward in movement than Galahad. Drank a lot too. Recently her gait got worse particularly on her back legs. We suspected arthritis and did catrophen injections. We also put her on non steroidal anti inflammatory drugs for pain. She vomited on the first type of NSAIDs and was prescribed another. Vomited again and I stopped them again. She started to really drool a lot and drink more water. And started to go further down hill, very fatigued, not lifting her head nor body much, wobbly back legs. She still ate well. She also developed lesions around her eye, nose and belly. These were microscoped and results were anti inflammatory and not bacterial. Thyroid blood test and red blood cell tests were good. Suspected dilated cardiomyopathy. Had heart ultrasound by specialist and heart was diagnosed as healthy. X-rays of chest looked good, perhaps showing very mild pneumonia if at all. She looked brighter on the antibiotics, and lesions improved, but her lethargy, drooling and wobbly back legs did not. Perhaps adverse reaction to NSAIDs to cause lesions? Off to internal medicine specialist for further blood tests and ultrasound of abdomen which all looked good. Urine test showed diluted result but otherwise good. Then neuromuscular specialists checked her swallowing and gag reflex. They were both weak. If they walked her around the hospital she fatigued easily and drooled more. Her back legs heavy and awkward. We have done blood tests now for Myasthenia Gravis, as well as other neuromuscular diseases. We have to wait two weeks for the results as they are in the US. In the meantime carry on with the antibiotics. Any advice would be appreciated. We are beside ourselves with worry. 😥

    1. Hi Lynn,
      I’m sorry I ‘m just seeing this now. I’m glad you found on the support groups and again, I am sorry about Morgan. Cancer is an awful disease. My sincere condolences.

  2. So my 2-year-old female Golden hasn’t been diagnosed yet, but titers are running and we’re pretty confident she has MG. She just has the neuromuscular symptoms in her legs after walking for an extended period of time. She has no problems eating at this point. I just have a few questions..
    – Do symptoms seem to progress from initial diagnosis? Ie. given that she (likely) does not have megaesophagus now, if left untreated will she eventually develop megaesophagus?
    – If we begin treatment ASAP (as soon as the titers are back) do symptoms seem to expand to incorporate more muscle groups? Does exercise intolerance tend to become more profound with time?

    Thanks! So glad I found this website.

    1. Hi David,
      The fear of the unknown is the biggest problem with myasthenia gravis. It’s like waiting for the other shoe to drop. We went through exactly that with our dog. He presented with hind leg weakness with an absence of megaesophagus. He never exhibited any signs of megaesophagus throughout his illness with MG. They say with humans, MG is like the snowflake disease since no two people with the disease exhibit the same symptoms. I think you could say the same for dogs. There seems to be a small percentage that never come down with ME. It is important to diagnose and start treatment as soon as possible. You may want to speak with your vet about starting a low dose of Pyridostigmine (mestinon) now and not to wait for results. Most people report their dog is walking better in a matter of 1 or 2 doses of pyridostigmine. I just saw you requested to join the facebook group so I’ll go ahead and approve you! Talk to you there!

    2. Our 7.5 year old golden retriever Riley was just diagnosed with acquired MG with megaesophagus. He came home with a Bailey chair from the hospital, which we have altered so it is more fitting and comfortable. He has a difficult time staying upright in it- he tries to get his front arms and head under the bar and his feet kick out. His meds are still being adjusted and he just seems to lose energy and tires out after a few minutes. I was hoping to hear about different positions that would be safe for him to eat in other than the Bailey chair. It takes 2 adults to help him during medication and meal times. We also have an 8 month old son at home, so trying to brainstorm ways to have Riley eat safely and be able to stay upright at 90 degrees is so difficult. Would some kind of wedge where he can lay on at a steeper incline work? Please share if you have ideas! We are trying so hard to help him and he really is the best dog in the world.

  3. I have a 6 year old Labrador who was diagnosed about 2 months ago with myasthenia. He does not have megaesophagus but has extreme weakness. Within a very short period of time he lost the ability to walk, lost his appetite and had no energy. After a strong Pred treatment he got better but was still pretty weak. Our second neurologist added Pyridostigmine and he was doing very well. Unfortunately he got a uti and a round of clavamox (we assume this was the culprit) set him back. He is currently on Pred twice a day, pyridostigmine 3 times a day and the neurologist wants to add in azathioprine. I have two small children and have read the dangers of the drug being present in the dogs saliva and urine and having to avoid them. Does anyone have experience using it? I am at a loss and it’s killing me seeing my big boy so down. His appetite is poor (which everyone knows is crazy for a lab) and he is very lethargic all of the time and struggles to move very far. Has anyone tried natural feeding with any good results? I’d literally try anything at this point.

    1. Hi Cody,
      Wow your dog sounds a like like ours was. Kodi also did not get megaesophagus with his myasthenia gravis. We too were on that same regiment of drugs. I don’t remember using any special precautions with the Azathioprine but I did read you should use rubber gloves to administer because the drug can be absorbed through the skin. Kodi did have some GI issue on this drug but we stuck it out and the weakness did subside. MG normally takes a good 6-8 months to resolve. Our dog took a full 18 months before he had a titer that was below 0.6. He did eventually go into full remission. I’m glad to hear they added in pyridostigmine. That is really what helps them to move again. I do not know of any natural feeding or supplement that can really help with this. We did find that adding in Cosequin DS, a joint supplement, and fish oil seemed to help Kodi but it had more to do with arthritis than the MG. Lethargy is a prominent symptom with MG. I know how hard it is to see them look so sad. I’m sure you will have your boy back to his old self soon. It’s good you are with a neurologist since they know more about the disease than most. Best of luck with your boy! Join the facebook groups Canine Megaesophagus Support Group and Upright Canine Brigade. That’s where they all are!

  4. Hi, my 6 year-old goldendoodle has a bunch of the symptoms for myasthenia gravis including not being able to swallow food (without feeding her the vertical way), drooling, getting tired more easy, change of voice, and not blinking normally. Just a few weeks ago, she was jumping after tennis balls into pools. We are meeting with an oncologist in about two weeks. Please, just tell me it is going to be ok.

    1. Hello Alexander!

      I saw that you found us on facebook! I’m just gonna tell you here, it will be okay! It is the strangest thing this disease. One minute they’re normal and the next something is really wrong. Keep feeding her vertically and follow the tips from the group. You may need to see a vet that specializes in neurological disorders sooner than 2 weeks. Ask for a referral to a Neurologist DVM. If you are near a teaching hospital that may be a good place to go. All specialist under one roof! She will need to be on pyridostigmine (mestinon) right away to control the symptoms. I wouldn’t delay. Talk to you on facebook!

    2. So sorry. Wish I could tell you that. But my Labradoodle is battling this now too. It’s so terrible. Hope your dog will be well.

      1. Hi Susan
        Hope your pup is better soon. If you haven’t already, please join our facebook group, Upright Canine Brigade and also Canine Megaesophagus Support Group. So much info and support there!

        Take Care,
        Donna

    1. Hi Celinda,
      Yes we definitely recommend a bailey chair. It is one of the best ways to keep a dog upright. There are alternatives though. If you have a very small dog or puppy you could use a baby high chair, baby walker, baby Bjorn or even a waste paper basket. For a larger dog, some have used a garbage trash can, paws up on the counter, paws up on the back of a sofa, having them eat on the stairs or a stepping stool. Making one is not difficult. It is basically a 3 sided box with a door and a tray or a paw bar. You can find out more on baileychairs4dogs.com. They have instructions on how to measure your dog, which is very important. Hope to talk to you more in group! Best of luck with your pup!

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