Can you classify your myasthenia gravis?

Case Series of Canine Myasthenia Gravis: A Classification Approach With Consideration of Seronegative Dogs

Rui Xavier Dos Santos, Jan Waelkens, Abbe H. Crawford, Sam Khan, Sara Sami, Sergio A. Gomes, Anouk Van Ham, Iris Van Soens, Ine Cornelis, Jake Canning, Joe Fenn, Patrick Waters, Sofie F. M. Bhatti, An E. Vanhaesebrouck

Background
Myasthenia gravis (MG) in dogs presents with diverse clinical forms and comorbidities, often complicating diagnosis and treatment. There is limited standardization in classifying these variants. This retrospective case series applies a structured classification system to MG in dogs to explore clinical features, treatment outcomes, and the relationship between MG subtypes and comorbid conditions.

Methods
A total of 94 dogs with confirmed MG (positive serum acetylcholine receptor antibody test) were retrospectively classified into five categories: focal, generalized, generalized with megaesophagus (ME), MG with thymoma, and fulminant MG. Data included signalment, clinical signs, imaging, treatment modalities, and outcomes. Diagnostic imaging assessed for thymoma, and responses to anticholinesterase and immunosuppressive therapies were recorded.

Results
Generalized MG with ME was the most common subtype (55%), followed by generalized without ME (20%), focal MG (11%), MG with thymoma (10%), and fulminant MG (4%). Dogs with ME had a significantly lower survival rate, especially if aspiration pneumonia occurred. Thymoma-associated MG cases responded variably to thymectomy and medical therapy. Focal MG often required only anticholinesterase drugs with favorable outcomes. Overall survival rates improved with early diagnosis and absence of severe comorbidities. Spontaneous remission occurred in a minority (15%).

Limitations
The retrospective nature and variability in diagnostic and treatment protocols limit the study's standardization. Not all dogs underwent thoracic imaging or follow-up testing, potentially underestimating the frequency of thymoma or remission. Selection bias toward referral populations may influence case representation.

Conclusions
Classifying MG in dogs based on clinical phenotype provides valuable insight into prognosis and therapeutic strategies. Generalized MG with ME carries the highest risk, and early, aggressive management is critical. Recognition of focal MG may reduce overtreatment. This classification system may help guide clinicians in prognosis, monitoring, and tailored treatment approaches.

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