Clinical features and outcome of acquired myasthenia gravis in 94 dogs

Background Factors known to be associated with outcome of acquired myasthenia gravis (MG) in dogs are limited. Hypothesis/Objectives Of dogs with MG, advancing age and comorbid neoplasia are associated with poor long‐term prognosis and low rates of remission. Animals Ninety‐four client‐owned dogs with MG diagnosed by acetylcholine receptor antibody (AChR Ab) assay between 2001 and 2019 from a university clinic and 3 private clinics in the United States. Methods Cases were retrospectively evaluated and data were collected to determine clinical signs, treatment, and response to therapy defined by means of a clinical scoring rubric. Immunological remission was defined as a return of the AChR Ab concentration to <0.6 nmol/L. Multivariable binary logistic regression analysis was used to identify clinical criteria predicting remission. Results An anticholinesterase drug was used to treat 90/94 (96%) dogs, which in 63/94 (67%) was the sole treatment; other drugs included immune modulators. Clinical remission (lack of clinical signs ≥4 weeks after treatment cessation) was observed in 29 (31% [95% confidence interval (CI): 22.4‐40.8%]) dogs, clinical response (lack of clinical signs on treatment) in 14 (15% [95% CI: 9.0‐23.6%]) dogs, clinical improvement (on treatment) in 24 (26% [95% CI: 17.8‐35.2%]) dogs, and no clinical improvement in 27 (29% [95% CI: 20.5‐38.6%]) dogs. Immunological remission was observed in 27/46 (59%) dogs, with clinical remission in all 27. Younger age ( P  = .04) and comorbid endocrine disease ( P  = .04) were associated with clinical remission. Initial AChR Ab concentration ( P  = .02) and regurgitation ( P  = .04) were negatively associated with clinical remission. Conclusions and Clinical Importance Clinical remission in MG is less likely in older dogs and dogs presenting with regurgitation or high initial AChR Ab concentration, but more likely in younger dogs and dogs with comorbid endocrine disease.