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Myasthenia Gravis in Dogs

Myasthenia Gravis in Dogs: Causes, Symptoms, and Treatments

Myasthenia gravis in dogs is a neuromuscular disorder that causes muscle weakness and fatigue due to impaired communication between nerves and muscles caused by an autoimmune disorder or is congenital due to a genetic defect.

Myasthenia gravis symptoms in dogs include muscle weakness (such as the facial muscles), exercise intolerance, and respiratory problems due to weakness in breathing muscles. Severe myasthenia gravis dog cases feature sudden collapse, especially after exertion.

Diagnosis for myasthenia gravis symptoms in dogs involves a veterinary examination to evaluate muscle strength, blood tests to detect the presence of elevated levels of antibodies against acetylcholine receptors, and an electromyography (EMG) test to measure the electrical activity in the muscles. A Tensilon test is performed during diagnosis.

Treatment for myasthenia gravis in dogs involves medication to improve neuromuscular transmission, including anticholinesterase or immunosuppressive drugs. Severely affected dogs require supportive care such as assisted feeding, intravenous fluids, and oxygen therapy.

What Is Myasthenia Gravis in Dogs?

Myasthenia Gravis in dogs is a neuromuscular disorder that leads to muscle weakness and affects the transmission of nerve signals at the neuromuscular junction. The disorder is an autoimmune disease in which antibodies attack acetylcholine receptors. “Myasthenia gravis is an acquired autoimmune disorder with autoantibodies against the neuromuscular junction (NMJ) of skeletal muscle in dogs,” according to the study by Mignan, T., Targett, M., & Lowrie, M. titled “Classification of myasthenia gravis and congenital myasthenic syndromes in dogs and cats,” 2020.

Myasthenia gravis occurs when the dog’s immune system targets acetylcholine receptors, disrupting the regular communication between nerves and muscles. The interference of a dog’s immunity results in muscle fatigue. Dogs affected by the condition experience weakness in various muscles controlling the eyes, jaw, neck, and limbs. The disease progresses, with symptoms like drooping eyelids, difficulty swallowing, and general weakness becoming evident.

How Do Dogs Get Myasthenia Gravis?

Dogs get myasthenia gravis due to genetics, immune system issues, thymoma, and environmental factors. Some dog breeds are more prone to myasthenia gravis due to genetic factors. “The dog breed "Gammel Dansk Honsehund" has an autosomal recessive inheritance of a neuromuscular disease resembling myasthenia gravis,” according to the study by Flagstad, A. titled “A new hereditary neuromuscular disease in the dog breed "Gammel Dansk Honsehund," Genetic investigations,” 2008. 

Dogd with myasthenia gravis experience immune system malfunctions, producing antibodies that target acetylcholine receptors. Thymomas or tumors that develop in the thymus gland trigger the autoimmune response that causes myasthenia gravis. Environmental factors such as infections and exposure to toxins play a role in the development of myasthenia gravis in dogs, but no specific triggers have been identified.

Malnutrition does not directly contribute to myasthenia gravis in dogs, while a nutritious diet gives the dog the energy and vitamins to develop a robust immune system to combat disease. Certain dog breeds are genetically predisposed to myasthenia gravis, but the specific mechanisms are not fully understood. 

How is Myasthenia Gravis Different from Bullous Pemphigoid in Dogs?

Myasthenia gravis is different from bullous pemphigoid in dogs since it affects muscle strength and the neuromuscular junction. Bullous pemphigoid is a skin disorder characterized by blistering. “Acute fulminating myasthenia gravis in dogs can cause sudden megaesophagus, muscle weakness, and respiratory failure, with rapid progression to quadriparesis if aspiration pneumonia develops,” according to the study by King, L., & Vite, C. titled “Acute fulminating myasthenia gravis in five dogs,” 1998. 

Bullous pemphigoid in dogs presents with widespread ulcerative skin lesions and oral mucous membrane involvement, often achieving remission within seven days with prednisolone therapy.

Distinguishing myasthenia gravis from bullous pemphigoid in dogs involves recognizing the unique clinical features that set them apart. Veterinarians conduct specialized tests for myasthenia gravis, like the Tensilon test, whereas skin biopsies diagnose bullous pemphigoid.

What Are the Symptoms of Myasthenia Gravis in Dogs?

The symptoms of myasthenia gravis in dogs are listed below.

  • Muscle Weakness: Muscular weakness is the hallmark of myasthenia gravis. Dogs exhibit generalized weakness, affecting various muscle groups throughout the body. Weakness is pronounced after periods of activity or exercise.
  • Exercise Intolerance: Dogs with myasthenia gravis tire easily during physical activity and are reluctant to exercise or play.
  • Facial Weakness: Weakness in the facial muscles causes drooping of the eyelids (ptosis), facial expression changes, and difficulty closing the mouth or maintaining a normal facial appearance.
  • Difficulty Swallowing (Dysphagia): Dogs with myasthenia gravis have difficulty swallowing food or water due to weakness in the muscles involved in chewing and swallowing. The difficulty leads to regurgitation of food or water, coughing, or choking.
  • Voice Changes: Weakness in the throat and larynx muscles changes the sound of the dog's bark. The bark sounds weaker or more hoarse than usual.
  • Respiratory Difficulty: Weakness in the breathing muscles leads to respiratory distress, panting, or difficulty breathing in severe cases of myasthenia gravis.
  • Collapse: Dogs with myasthenia gravis sometimes experience sudden collapse or weakness after exertion or during stress.

How Is Myasthenia Gravis Diagnosed in Dogs?

Myasthenia gravis in Dogs is diagnosed through clinical evaluation, laboratory tests, and specialized diagnostic procedures.

The diagnosis of myasthenia gravis in dogs involves a physical exam and blood tests performed by a veterinarian. The blood test measures antibodies against acetylcholine receptors, and elevated levels confirm myasthenia gravis diagnosis. “Myasthenia gravis in dogs is diagnosed through an autoimmune response against nicotinic acetylcholine receptors and autoantibodies against acetylcholine receptors implicated in the pathogenesis,” according to the study by Shelton, G. titled “Myasthenia gravis and congenital myasthenic syndromes in dogs and cats: A history and mini-review,” 2016. 

A Tensilon test is performed while waiting for blood test results to diagnose myasthenia gravis. The method involves administering a dose of Tensilon, and any improvement in muscle weakness within minutes indicates a positive result. 

Chest X-rays examine the thymus gland for abnormalities, such as thymomas, associated with the condition. Antibody screenings identify the presence of acetylcholine receptor antibodies found in dogs with myasthenia gravis.

What Causes Myasthenia Gravis in Dogs?

The causes of myasthenia gravis in dogs are listed below.

  • Genetics: Certain dog breeds have a higher predisposition to developing myasthenia gravis, suggesting a genetic component to the disease. 
  • Immune System Dysfunction: Dogs with myasthenia gravis exhibit immune system malfunctions and produce antibodies that target the acetylcholine receptors. The autoimmune reaction destroys or blocks acetylcholine receptors, impairing neuromuscular transmission and resulting in muscle weakness.
  • Thymoma: Dogs develop tumors in the thymus gland called thymomas in certain cases of canine myasthenia gravis. The thymus gland develops and regulates the immune system. Thymomas trigger or exacerbate the autoimmune response that leads to myasthenia gravis symptoms in dogs.
  • Environmental Factors: Environmental triggers, such as infections or exposure to certain toxins, contribute to autoimmune diseases like myasthenia gravis. Conclusive environmental triggers for myasthenia gravis in dogs have not been identified.

What Triggers Myasthenia Gravis?

The triggers of myasthenia gravis in dogs are associated with the production of antibodies that interfere with neuromuscular function. Myasthenia gravis is a muscle weakness condition caused by immune system dysfunction, genetics, environmental factors, infections, hormonal changes, stress, and certain medications. 

The immune system disrupts neuromuscular transmission and produces antibodies that attack healthy cells. Certain infections and medications trigger or worsen myasthenia gravis, while hormonal changes and stress influence its onset or worsening.

Dogs predisposed to autoimmune diseases have immune cells that activate and produce antibodies that target acetylcholine receptors. The autoimmune response disrupts neuromuscular transmission and leads to muscle weakness. 

Environmental triggers include exposure to infectious agents, toxins, or other environmental stressors that activate the immune system and precipitate an autoimmune response. Viral or bacterial infections stimulate the immune system and promote the production of autoantibodies against acetylcholine receptors. 

Hormonal changes influence the onset or exacerbation of myasthenia gravis, as evidenced by the increased incidence of myasthenia gravis in females during reproductive years and following childbirth. Fluctuations in hormone levels, such as estrogen, progesterone, and testosterone, modulate immune function and contribute to autoimmune reactions.

Psychological or physical stressors are associated with triggering autoimmune diseases, including myasthenia gravis. Stress activates the hypothalamic-pituitary-adrenal (HPA) axis and releases stress hormones, which modulate immune responses and potentially exacerbate autoimmune reactions in susceptible individuals.

Certain medications, such as antibiotics, muscle relaxants, and some cardiovascular drugs, are associated with the development or exacerbation of myasthenia gravis. The medications alter neuromuscular function or immune responses, contributing to the onset or worsening of myasthenia gravis symptoms.

Can Myasthenia Gravis in Dogs Be Hereditary?

Yes, myasthenia gravis in dogs can be hereditary. There is ongoing research into the disease's hereditary aspects, and genetic testing helps identify inherited forms of the disease. 

“Myasthenia gravis in dogs can be hereditary, as congenital myasthenic syndrome (CMS) has been described in Brahman calves and Jack Russel Terrier puppies,” Herder, V., Ciurkiewicz, M., Baumgärtner, W., Jagannathan, V., & Leeb, T. titled “Frame-shift variant in the CHRNE gene in a juvenile dog with suspected myasthenia gravis-like disease,” 2017.

Genetic testing aids in early detection and is a preventive measure for inherited diseases. Incorporating genetic testing into routine veterinary care ensures a better quality of life for dogs at risk.

What Are the Treatment Options for Myasthenia Gravis in Dogs?

The treatment options for myasthenia gravis in dogs are listed below. 

  • Medications: Acetylcholinesterase inhibitors such as pyridostigmine bromide improve neuromuscular transmission by inhibiting acetylcholinesterase, which breaks down acetylcholine. The event leads to increased levels of acetylcholine at the neuromuscular junctions, alleviating muscle weakness and fatigue. Immunosuppressive drugs such as corticosteroids suppress the abnormal immune response and reduce the production of antibodies that target acetylcholine receptors. The drugs help to control inflammation and prevent damage to neuromuscular junctions.
  • Thymectomy: Surgical removal of the thymoma (tumor of the thymus gland) and the entire thymus gland is recommended if a thymoma is present and contributes to the autoimmune response. Thymectomy reduces antibody production and improves myasthenia gravis symptoms in cases where thymoma is associated with the disease.
  • Supportive Care: Supportive care manages myasthenia gravis in dogs symptoms and maintains their overall health, including a balanced diet, adequate hydration, and monitoring for complications such as aspiration pneumonia. Physical therapy and rehabilitation exercises improve muscle strength and coordination in dogs.
  • Monitoring and Adjustment of Treatment: Regular visits to a veterinarian assess the dog's response to treatment, monitor for medication side effects, and adjust the treatment plan as needed. Dogs with myasthenia gravis experience fluctuations in symptoms over time, so treatment must be modified based on changes in clinical signs and disease progression.
  • Emergency Treatment: Dogs experience respiratory distress or crisis in severe cases of myasthenia gravis, requiring emergency intervention. The treatment involves hospitalization, oxygen therapy, intravenous fluids, and mechanical ventilation to support respiratory function until the dog stabilizes.

How Does Myasthenia Gravis Affect a Dog's Muscles?

Myasthenia gravis affects a dog's muscles by disrupting nerve signals at the neuromuscular junction, leading to muscle weakness, fatigue, and difficulty in movement. The condition occurs when the immune system targets receptors that receive signals from nerve cells, causing a breakdown in communication between nerves and muscles. 

Impaired nerve signals prevent contraction and relaxation of muscles, resulting in weakness that worsens with activity. Dogs with myasthenia gravis experience drooping eyelids, reduced bark strength, and difficulty swallowing as the disease progresses. “Myasthenia gravis is an autoimmune disease that causes autoantibodies to be directed against muscle postsynaptic nicotinic acetylcholine receptors, leading to generalized neuromuscular signs in dogs,” according to the study by Kent, M., Glass, E., Acierno, M., & Shelton, G. titled “Adult onset acquired myasthenia gravis in three Great Dane littermates,” 2008.

Are There Specific Dog Breeds That Are More Prone to Myasthenia Gravis?

Yes, there are specific dog breeds that are more prone to myasthenia gravis. “Acquired myasthenia gravis in dogs is more common in Akitas, terrier groups, Scottish Terriers, German Shorthaired Pointers, and Chihuahuas, with breed predispositions, age, and sex being contributing factors,” according to the study by Shelton, G., Schule, A., & Kass, P. titled “Risk factors for acquired myasthenia gravis in dogs: 1,154 cases (1991-1995),” 1997.

Certain breeds have a higher incidence of myasthenia gravis, but the condition manifests in any breed or mixed-breed dog. Individual genetic factors, environmental factors, and immune systems contribute to myasthenia gravis.

What Is the Life Expectancy of Dogs with Myasthenia Gravis?

The life expectancy of dogs with myasthenia gravis depends on the severity of the condition and the effectiveness of treatment. “48% of dogs with acquired myasthenia gravis died or were euthanized shortly after admission to the hospital due to aspiration pneumonia,” according to the study by Dewey, C., Bailey, C., Shelton, G., Kass, P., & Cardinet, G. titled “Clinical forms of acquired myasthenia gravis in dogs: 25 cases (1988-1995),” 1997.

Dogs who respond well to medication and therapy generally have better prognoses. “Congenital myasthenia gravis in Smooth-Haired Miniature Dachshund dogs resolves spontaneously by 6 months of age, making it a rare but potentially treatable condition in dogs,” according to the study by Dickinson, P., Sturges, B., Shelton, G., & Lecouteur, R. titled “Congenital myasthenia gravis in Smooth-Haired Miniature Dachshund dogs,” 2005. Monitoring the disease progression allows veterinarians to adjust treatment plans and positively affect myasthenia gravis in dogs life expectancy.

What Are the Signs of Sudden Onset Myasthenia Gravis in Dogs?

The signs of sudden onset myasthenia gravis in dogs are listed below.

  • Generalized Weakness: Dogs exhibit sudden weakness or lethargy, with a noticeable decrease in energy levels and activity.
  • Exercise Intolerance: Dogs become fatigued quickly during physical activity or exercise and are reluctant to engage in play or walks.
  • Difficulty Swallowing (Dysphagia): Sudden-onset myasthenia gravis causes difficulty swallowing food or water due to weakness in the muscles involved in chewing and swallowing. Dogs drool excessively or show signs of discomfort when eating or drinking.
  • Facial Weakness: Weakness in the facial muscles causes drooping of the eyelids (ptosis), changes in facial expression, and difficulty closing the mouth or maintaining normal facial symmetry.
  • Change in Bark Sound: Dogs exhibit a change in the sound of their bark, which becomes weaker or more hoarse than usual due to weakness in the throat and larynx muscles.
  • Respiratory Distress: Dogs experience respiratory distress or difficulty breathing due to weakness in the respiratory muscles in severe cases of sudden onset myasthenia gravis, which manifests as rapid or difficult breathing, panting, or gasping for air.
  • Collapse or Paralysis: Sudden onset myasthenia gravis leads to collapse or paralysis in extreme cases if respiratory muscles are affected. Dogs become unable to stand or move normally.

Can Myasthenia Gravis in Dogs Lead to Other Health Complications?

Yes, myasthenia gravis in dogs can lead to other health complications like megaesophagus, which increases the risk of aspiration pneumonia due to swallowing difficulties. “Megaesophagus secondary to myasthenia gravis in a female German shepherd dog led to worsening regurgitations and aspiration pneumonia, ultimately necessitating euthanasia,” according to the study by Andrade, S., Nogueira, R., Melchert, A., Patrícia, M., Silva, C., Motta, Y., Brinholi, R., AlbertoTostes, R., & Sanches, O. titled “Megaesophagus secondary to myasthenia gravis in a German Shepherd dog,” 2007.

Untreated or poorly managed myasthenia gravis in dogs results in other health complications, such as aspiration pneumonia, which occurs when food or water enters the airway instead of the esophagus due to weak muscles responsible for swallowing. Difficulty eating and swallowing lead to reduced food intake, weight loss, and nutritional deficiencies, which cause malnutrition and weight loss. Chronic fatigue and weakness significantly impact a dog's quality of life, reducing mobility, exercise intolerance, and discomfort. 

Medications used to treat myasthenia gravis, such as immunosuppressants or corticosteroids, have side effects or complications, including gastrointestinal upset, increased susceptibility to infections, and metabolic changes. Dogs with untreated myasthenia gravis experience sudden worsening of symptoms, known as myasthenic crisis. The condition is life-threatening if not promptly addressed with supportive care and medication adjustments.

Is Myasthenia Gravis Considered an Autoimmune Disease?

Yes, myasthenia gravis is considered an autoimmune disease in dogs. The condition is characterized by antibodies targeting acetylcholine receptors at the neuromuscular junction. 

The immune-mediated nature of the disease underlines its autoimmune origins. “Early, accurate diagnosis and appropriate therapy are crucial for a good clinical outcome,” according to the study by Shelton, G. titled “Myasthenia gravis and disorders of neuromuscular transmission,” 2002.

The exact cause of the autoimmune response in myasthenia gravis is believed to be a combination of genetic predisposition and environmental factors triggering the immune system's abnormal response. Infections, hormonal changes, and certain medications have been documented as triggers or exacerbating factors in susceptible individuals.

Myasthenia gravis is characterized by its autoimmune component, with variations in the specific immune mechanisms involved. Some cases have additional complexities beyond a standard autoimmune disease in dogs. Myasthenia gravis involves immunosuppressive medications to modulate the immune response and reduce antibody production.