What Is Myasthenia Gravis (MG) in Dogs?
Myasthenia Gravis (MG) in dogs is an autoimmune disorder characterized by varying degrees of muscle weakness. It disrupts the normal communication between nerves and muscles, hampering the transmission of signals essential for movement and muscle contractions.
Nerves are responsible for transmitting signals to the muscles, but in MG, this process is impaired. The immune system produces antibodies that target and inhibit the acetylcholine receptors, crucial for transmitting nerve signals to the muscles. Consequently, nerves struggle to fulfill their function, leading to muscle weakness and compromised movement.
Aside from physical weakness, MG can also impact a dog’s mental well-being due to its debilitating nature. Any noticeable changes in your dog’s physical or mental state should prompt a visit to the veterinarian for proper evaluation and management.
Symptoms
Myasthenia Gravis (MG) in dogs manifests in three distinct forms:
- Generalized MG: This variant affects approximately 57% of dogs with acquired MG. Symptoms may consist of:
- Stiffness induced by exercise, alleviated by rest
- Tremors
- Pronounced and worsening weakness
- Persistent fatigue
- Megaesophagus
- Focal MG: Symptoms of this form may include:
- Weakness in facial, throat, and esophageal muscles
- Alteration in bark
- Weakness localized in specific body parts
- Fulminant MG: This is the rarest form of MG, characterized by symptoms such as:
- Sudden reduction in muscle tone
- Megaesophagus
- Rapid onset of paralysis in muscles crucial for breathing
Should you observe any of the aforementioned symptoms in your dog, it is imperative to seek immediate assistance from an emergency veterinarian.
Causes
Myasthenia Gravis (MG) in dogs can stem from either inherited (genetic) factors or acquired causes, with acquired MG being more prevalent than the inherited form.
MG is not exclusive to dogs and cats; it can also affect humans. This neuromuscular disease arises from a deficiency in acetylcholine receptors present on muscle cell surfaces. This deficiency disrupts the transmission of signals between nerves and muscles, leading to muscle weakness across various parts of the body and subsequent extreme fatigue in affected dogs.
Certain breeds are predisposed to congenital MG, meaning they are born with the condition. These breeds include Jack Russell Terriers, English Springer Spaniels, Smooth Haired Fox Terriers, and Smooth Haired Miniature Dachshunds. Dogs with inherited MG typically exhibit fewer receptors and are often diagnosed before reaching one year of age.
On the other hand, acquired MG is more frequently observed in older dogs, including Newfoundlands, Great Danes, Golden Retrievers, Akitas, and Scottish Terriers. Environmental, infectious, or hormonal influences can contribute to acquired MG by adversely affecting the immune system. This results in the production of antibodies against receptors, impeding muscle movement.
Acquired MG is commonly associated with conditions such as chest tumors (thymoma) and can also be linked to hypothyroidism.
Diagnosis
When observing any alterations in your dog’s physical or mental condition, prompt veterinary attention is essential. Capturing a video of your dog’s behaviors can be beneficial for showcasing symptoms, especially those induced by exercise, to your vet during appointments.
During the veterinary visit, a thorough physical examination will be conducted, accompanied by an analysis of your dog’s bloodwork, including thyroid hormone levels. Diagnosis of MG in dogs involves measuring antibodies against acetylcholine receptors in a blood sample. Elevated levels of these antibodies confirm MG and serve as indicators for monitoring treatment response. As this blood test necessitates analysis in a specialized laboratory, results may take several days to weeks.
If MG is suspected based on clinical signs or breed predisposition, a Tensilon test may be conducted while awaiting blood test results. This involves administering an intravenous injection to the dog. A positive response to the injection, with immediate improvement in weakness and other symptoms, confirms MG. However, this relief is transient, lasting only a few minutes.
Furthermore, chest X-rays are performed to assess for conditions like megaesophagus, aspiration pneumonia, or cancer. Aspiration pneumonia arises as a secondary consequence of regurgitation and muscle weakness in the throat.
Treatment
While there is no cure for Myasthenia Gravis (MG) in dogs, effective treatment options exist for managing the condition. The choice of treatment depends on the type of MG diagnosed in your dog and the associated symptoms.
The primary medication used in MG treatment for dogs is pyridostigmine bromide, which enhances muscle function by prolonging the presence of acetylcholine in the receptors on muscle cells, facilitating coordinated movement.
In some cases, prednisone or other steroid medications may be prescribed to suppress the immune system, thereby mitigating the immune response underlying MG. Additionally, if hypothyroidism is present, lifelong administration of levothyroxine sodium is typically recommended to manage the condition.
Dogs with megaesophagus require special feeding protocols to prevent complications such as aspiration pneumonia. They should be fed in an elevated position, either using an elevated food bowl or a specialized “Bailey chair” to maintain an upright posture during meals. Feeding smaller, more frequent meals throughout the day is advisable, and dogs should remain upright or in the chair for 20 to 30 minutes after eating to minimize the risk of aspiration.
In cases where a thymoma tumor is detected, surgical removal may be considered if the dog’s health permits such an operation. This option is contingent upon the individual dog’s overall health status and suitability for surgery.
Living and Management
Recovery and management of Myasthenia Gravis (MG) in dogs hinge on various factors such as the dog’s clinical presentation, the specific type of MG diagnosed, and any underlying causes.
A diagnosis of MG typically carries significant gravity, with prognosis varying widely. Early detection and treatment offer a better chance of achieving remission, although some dogs may require lifelong management.
Dogs afflicted with aspiration pneumonia face a less promising prognosis, particularly if they experience respiratory difficulties or harbor chest tumors. The severity of complications associated with aspiration pneumonia can significantly impact the overall outlook for affected dogs.
Prevention
Currently, there are no known methods to prevent Myasthenia Gravis (MG) in dogs.
Myasthenia Gravis (MG) FAQs
How long can a dog live with myasthenia gravis?
The life expectancy of a dog with myasthenia gravis varies depending on the root cause of the condition. With proper medical supervision and management, dogs can live for many years. However, those with chest tumors typically have a less optimistic prognosis.
What triggers myasthenia gravis in dogs?
Myasthenia gravis (MG) in dogs can stem from inherited or genetic factors. It can also be acquired, often triggered by conditions like hypothyroidism or the presence of a chest cavity tumor, such as a thymoma.