Acquired Myasthenia Gravis in Cats: Understanding the Risks and Outcomes


When it comes to our furry friends, their health and well-being are of utmost importance. One condition that can affect cats is Acquired Myasthenia Gravis (MG). From 2001 to 2012, a study conducted at the Comparative Neuromuscular Laboratory, University of California, San Diego, diagnosed this condition in 235 cats. Let’s delve into the results to gain a better understanding of the risk factors and outcomes associated with Acquired Myasthenia Gravis in cats.

Risk Factors

The study found that males and females were equally affected by Acquired Myasthenia Gravis. Additionally, it was discovered that mixed breed cats were more commonly affected (80.4%) compared to purebred cats (19.6%). However, some breeds had a higher odds ratio of developing MG, namely Abyssinian (OR = 4.97) and Somali cats (OR = 11.60). Although the timing of vaccination and its relation to the onset of clinical signs could not be determined definitively due to limited data, it is worth noting that five cats were receiving methimazole treatment for hyperthyroidism at the time of MG diagnosis.

Clinical Signs

Clinical signs varied among the cats diagnosed with MG. Some cats presented with generalized appendicular muscle weakness without regurgitation or dysphagia (50%), while others exhibited focal clinical signs such as regurgitation or dysphagia without generalized weakness (10%). There were also cats who experienced generalized weakness along with regurgitation and dysphagia (40%). Thoracic radiographs revealed that megaesophagus was present in some cats, while aspiration pneumonia was noted in others. Interestingly, the presence of a mediastinal mass did not affect the clinical presentation.

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Cranial Mediastinal Mass and Histopathologic Diagnosis

In the medical records of 133 cats, a cranial mediastinal mass was observed in 69 cats (52%). The histopathologic diagnosis of the mass revealed that thymoma was present in 35 cats (97.7%), while lymphoma was present in only one cat (2.3%).

Treatment Approaches

Cats diagnosed with MG were treated using various approaches. Some cats received medical management only (82 cats), others underwent surgery only (5 cats), and some had a combination of medical and surgical management (35 cats). Medical treatment included the use of steroids, pyridostigmine, and other immunomodulatory medications.

AChR Antibody Titers

AChR antibody titers were performed in 54 cats, with some cats having thymoma and others not. Among the cats with thymoma, a decrease in AChR antibody titers was observed in 57% of cases, while an increase was noted in 24% of cases. Cats without thymoma did not show an initial increase in antibody titers and had a decrease in titers in 73% of cases. Overall, cats with thymoma did not enter immune remission, as continued medication was necessary and antibody titers remained elevated.


The medical records of 56 cats indicated the presence of comorbidities alongside MG. These comorbidities included heart murmurs, cardiomyopathy, hyperthyroidism, diabetes mellitus, and pneumonia, among others.

Clinical Outcomes

Outcomes varied among the cats diagnosed with MG. At the time of the study, only 38% of the cats were alive, while 4% had passed away, and 58% were euthanized. Spontaneous remission was observed in only a small number of cats. Survival time was negatively correlated with the value of the antibody titer, indicating that cats with higher antibody titers had a shorter survival time.

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To learn more about Acquired Myasthenia Gravis in cats and how to support their health, visit Katten TrimSalon.

In conclusion, Acquired Myasthenia Gravis is a complex condition that can affect cats of any breed. Understanding the risk factors and outcomes associated with this condition can help cat owners and veterinarians provide the best care possible for their furry companions.