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!

140 thoughts on “Myasthenia Gravis

  1. We just received our Bailey Chair. Our Dog relax more when I hold him like a baby, padding him on his chest, and talking to him at the same time.

  2. I could not believe that dogs suffer from MG , I am 81 yrs old, I have had it since 2005. Thank you for the information. I sounds like my life.

    1. We have a Canine Myasthenia Gravis face book group with human MG members that comment on the group. It is very interesting how in some ways it affects dogs and humans the same. In other ways it is very different. With dogs the biggest battle is megaesophagus and aspiration pneumonia. On the flip side many go into spontaneous remission and some dogs never look back! It is definitely a “snowflake” disease in both humans and animals. Thank you for reading! Best of luck with your MG!

  3. I’m positive my dog has MG. He’s been in and out of the hospital. The vet will not perform the blood test because she’s sure he does not have it. He’s on predestorone and antibiotics still. Can he have the blood test? Or will the steroids ruin the result? He’s lethargic still, can’t jump up to the cough, appetite us decreased, and he hacks up mucus.
    We’ve spent over 6k with no diagnosis. They want us to euthanize him!

    1. Hi Jeanette,
      Steriods do effect the results of the AChR antibody titer test for MG. There is a tensilon test they could perform if he is showing weakness. I would ask your vet about that. You may need to see a specialist. When ME comes on suddenly, MG should always be tested for along with Hypothyroidism and Addison Disease. All 3 can be contributors to that kind of weakness. Controlling the regurgitation is very important right now. Some dogs need a pro-motility drug and an antacid. The pro-motility drug will help move food out of the stomach faster so that there is room for the next meal and the antacid will help cut down on acid reflux that they suffer from sometimes. Be sure to manage his ME in a bailey chair or in a upright position. A neck hug at night is very important. It keeps saliva from pooling in the esophagus. Please join the facebook groups for more good ideas and suggestions. Best of luck on your journey.

    2. Hi Janette,
      Our vet referred us to a specialist (neurologist). It was how we found out our dog has MG. Best of luck in finding help for your dog.

  4. It’s now been nearly 2 years since my pug x has been diagnosed with myathensia gravis and megaesophagus. It took a lot of different vets to figure out what was wrong with her. She was fine one day and then the next she couldn’t keep anything down and had the shakes for days. She developed pneumonia and I thought this was the end. Miracously after finding a dedicated vet they diagnosed her and put her on mestinon twice a day and she’s now been the best she’s ever been since getting sick. She still regurgitates daily but she’s the happiest dog and is in no pain. I’m constantly vigilant looking for signs for progression of her disease or pneumonia. I know how devastating this diagnosis is but in some cases your fur baby’s can improve! I’m so happy I didn’t listen to the first vet who told me to put my baby down! This disease may not be curable but it can definitely be manageable !

    1. That’s wonderful news Natasha. I so agree. The diagnosis can be a heavy blow but once you get it managed they can live perfectly normal lives!

  5. My 9 year old as MG and pneumonia as well He is on Enrofloxacin, and Clavamox, he was treated with both while at the vet and when we brought him home due to the high cost of vet hospitals, can I let him go outside? We just brought him home today and he is vomiting up foam, I am hoping it is a good sign that the medication is working, still not eating although he did try to drink some water but It came right back up before I had a chance to run over and lift him up. I don’t know what else I can do i’m losing my mind over this

    1. Hi Ruben,
      The first few weeks are difficult with MG. You may ask your vet about using an antacid along with the mestinon. Be sure that the mestinon is taken with food. At night in particular, a neck hug is very helpful to prevent regurgition. It keeps the head elevated so that saliva can properly drain down. Hang in there. I know how tough the early stages of this disease is to manage. It can be done. Keep in close contact with your vet especially concerning dosing of the MG meds. Keep a log book of everything you are observing i.e reactions to meds, progress with meds or set backs. There is a lot of help out there on facebook. I would recommend Canine Megaesophagus Support Group, Upright Canine Brigade and Canine Myasthenia Gravis Support Group. Best of luck!

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