Myasthenia Gravis in Dogs: What Owners Need to Know

Does your once playful pup suddenly seem exhausted after even the shortest walks? Are they regurgitating food and water even though they seem hungry? These could be signs of myasthenia gravis in dogs, a neuromuscular disease where the communication between the nerves and muscles gets disrupted. While a serious condition that can deeply impact your dog's quality of life, knowing what to look for and understanding myasthenia gravis is the first step towards getting them the help they need.

Understanding the basics of myasthenia gravis in dogs

Let's break down what's actually happening inside your dog's body when they have myasthenia gravis (MG).

• The messengers: Think of your dog's nerves like messengers carrying instructions to their muscles. These messages tell their muscles to move – to wag a tail, lift a leg, or take a deep breath.
• The signal: For those messages to get through, nerves release a special chemical called acetylcholine. This chemical binds to acetylcholine receptors on the muscle, triggering it to work (leading to muscle contraction).
• The broken link: In myasthenia gravis in dogs, there's a problem at the point where the nerve and muscle meet, called the neuromuscular junction. This makes it difficult for the muscle to receive the nerve's signals and move properly.
• Breeds at risk: German shepherd, Akita, golden retriever, Dachshund, and Labrador retriever are predisposed to myasthenia gravis. MG tends to affect dogs younger than 5 or older than 7 years, with a higher prevalence in females. While MG can affect dogs and cats, it's most common in dogs.

Types of myasthenia gravis

It's important to know there are two main types of myasthenia gravis:

1. Congenital: Some puppies are born with MG due to a genetic issue. Thankfully, this is much less common. This form is typically diagnosed in puppies at 4-16 weeks of age.
2. Acquired: The vast majority of dogs with MG develop it later in life. In this form, their immune system gets confused and attacks its own body, including those important muscle receptors. The acquired form typically occurs between 1-4 years or 9-13 years of age.

What are the causes of myasthenia gravis in dogs?

As mentioned above, there are two main forms of myasthenia gravis, each with its own cause:

1. Acquired Myasthenia Gravis (most common)

In most dogs with acquired MG, their own immune system starts attacking a key part of the connection between nerves and muscles. It's like the body's defense system sees a vital component as an enemy. Therefore, MG is classified as an autoimmune disease.

What Triggers This? The exact cause is still being researched, but it might involve:

• Issues with the thymus gland (part of the immune system)
• A tumor that activates the immune system incorrectly (paraneoplastic syndrome)

2. Congenital Myasthenia Gravis (less common)

Unlike the acquired form, the congenital form is not considered to have an autoimmune component. Some puppies inherit a genetic issue preventing their nerve-muscle connections from working properly.

In addition to German Shepherds, and Labrador retrievers, other breeds, like Jack Russell Terriers, Fox Terriers, and Springer Spaniels, can be more prone to this.

Signs and symptoms of myasthenia gravis in dogs

The most common sign of myasthenia gravis in dogs is muscle weakness that gets worse with exercise but improves after rest. Other clinical signs you might notice include:

• Generalized weakness: Your dog tiring out quickly on walks, struggling with stairs, or having a hard time holding their head up.
• Regurgitation: Difficulty swallowing food and water, leading to regurgitation (this looks different from forceful vomiting). This occurs because MG often causes a weakened esophagus, called megaesophagus.
• Changes to eating: Trouble chewing, excessive drooling, or seeming hungry but unable to eat much.
• Altered bark: Their bark sounds weaker or hoarse due to weakened throat muscles.
• Inability to blink: This can make their eyes dry and appear irritated.
• Episodic weakness: Periods of collapse or extreme muscle weakness, often triggered by activity.
• Breathing trouble: In severe cases, difficulty breathing is due to weakened respiratory muscles.

Not every dog shows all these signs, and the severity can vary a lot between dogs. Even slight changes, like your dog seeming a bit clumsier than usual, are worth discussing with your veterinarian.

How is myasthenia gravis diagnosed in dogs?

Diagnosis of myasthenia gravis begins by excluding other causes of intermittent weakness. This requires a comprehensive assessment, including a variety of diagnostic tests.

Here's what you can usually expect during the diagnosis process:

1. Discussing your dog's history: Your vet will start by asking detailed questions about:
   • The symptoms you've noticed and when they started.
   • Your dog's overall health and any medications.
   • If your dog's breed is known to be prone to MG.
2. Thorough physical exam: The vet will check your dog's reflexes, muscle strength, and look for signs like difficulty swallowing or breathing issues.
3. Possible blood tests: These serve a few purposes:
   • Rule out other conditions that can cause similar symptoms.
   • Look for antibodies that indicate acquired MG (the most common type). This test is very reliable and is considered the gold standard for diagnosing MG.
   • Check your dog's general health before starting treatment.
4. Specialized tests (If needed): Sometimes these are needed to confirm the diagnosis or in cases where the blood test is negative:
   • Tensilon test: A short-acting medication is given to see if your dog's muscle weakness temporarily improves (a positive sign of MG). After administering the injection, improvement is often noticed within minutes.
   • Chest X-rays: To check for megaesophagus (dilated esophagus) or any signs of pneumonia related to swallowing problems. Chest X-rays can also help visualize the thymus if it is enlarged.

Important to remember: It might take a few steps to get a definitive diagnosis and don't be afraid to ask your vet questions and discuss any concerns you have. While hearing your dog has MG can be scary, it's the first step toward helping them feel better and manage their condition.

What is the treatment for dogs with myasthenia gravis?

While there's no cure for MG, with proper treatment, dogs have the potential to live happy and fulfilling lives. Here's an overview of what treatment focuses on:

1. Medications:
   • Pyridostigmine is the most common medication for MG. It helps signals get from nerves to muscles more effectively, improving strength and reducing symptoms. Technically, these medications work longer at muscle junctions, improving communication between nerves and muscles.
   • For some dogs, immunosuppressive medications (like prednisone or azathioprine) might be needed in addition to pyridostigmine.
2. Treating Complications:
   • Megaesophagus: Special feeding positions (like using an elevated bowl or Bailey chair), smaller and more frequent meals, and keeping your dog upright after eating can help prevent aspiration pneumonia.
   • Aspiration Pneumonia: This serious complication often requires antibiotics. Severe cases might need hospitalization for supportive care.
3. Surgery:
   • If a tumor in the chest is linked to MG, such as a thymoma, your vet will discuss whether surgery to remove it is an option.

Important notes: Every dog responds differently to MG treatment, so your vet will create a plan based on the test results and tailored specifically for your pet. Some dogs even go into remission, meaning their symptoms might improve enough to reduce or even stop medication.

Complications of myasthenia gravis

One of the most serious complications of MG is the development of megaesophagus. This means the esophagus (the tube connecting the mouth to the stomach) becomes enlarged and loses its ability to move food down properly. This can make it difficult for your dog to swallow, leading to food and water getting regurgitated.

Sadly, a major risk with megaesophagus is aspiration pneumonia. This occurs when food, liquid, or even saliva accidentally goes into the lungs instead of the stomach. This can cause severe pneumonia requiring intensive treatment.

Recognizing the signs:

• Pay close attention to how your dog eats and drinks. Signs of megaesophagus include:
  • Regurgitating food and water shortly after eating. Abdominal contractions or bile, common signs of vomiting, will be absent.
  • Weight loss even if they seem hungry.
  • Coughing, gagging, labored, or trouble breathing.

Managing these complications:

If your dog develops megaesophagus, your vet will work with you on strategies like:

• Feeding positions: Using elevated bowls or a special chair to keep them upright while they eat and for a while afterward. A Bailey chair is often used for this purpose.
• Diet changes: Softer foods or a slurry consistency might be easier to manage.
• Medications: Sometimes medications such as metoclopramide or cisapride can help the food move food along.

If you suspect aspiration pneumonia in your dog, contact your veterinary team immediately. This often requires antibiotics and, in severe cases, hospitalization.

FURTHER READING: Read our article on megaesophagus where we discuss how to manage it in greater detail.

What is the prognosis for dogs with myasthenia gravis?

The outlook for dogs with myasthenia gravis depends on several factors, including the type of MG, how severe it is, and their individual response to treatment. Here's a breakdown:

Acquired Myasthenia Gravis

• This is the most common form in dogs, and thankfully, the prognosis is generally good with treatment.
• Most dogs see significant improvement in their symptoms, allowing them to live full and active lives.
• Some dogs even go into remission, meaning they might not need ongoing medication.
• However, a thymus gland tumor carries a less-than-favorable prognosis.

Congenital Myasthenia Gravis

• This form is less common and sadly carries a more guarded prognosis.
• While treatment can help manage symptoms, it might be a more challenging lifelong condition.

With either form, the limiting factor appears to be the development of aspiration pneumonia. Dogs that develop aspiration pneumonia, especially on more than one occasion, have a worse prognosis. Unfortunately, multiple studies have documented a 1-year mortality rate ranging from 40% to 60%.

Myasthenia gravis is a neuromuscular disease in dogs and the two main types are congenital and acquired. The acquired form is more common and generally carries a better prognosis compared to the congenital form. The main symptoms of myasthenia gravis in dogs are muscle weakness, fatigue, and regurgitation of food/water. Your veterinarian can diagnose based on a blood test that checks for specific antibodies (acetylcholine receptor antibody). Treatment typically involves medication that helps improve muscle function and prevent aspiration pneumonia, a serious complication of the disease. If you have any questions about myasthenia gravis affecting your dog, please contact your veterinarian.