Risk factors for acquired myasthenia gravis in cats: 105 cases (1986-1998)

Objective-To determine prevalence of initial clinical signs and risk factor s for acquired myasthenia gravis (MG) in cats. Design-Retrospective case-control study. Animals-105 cats from the United States, Canada, and the United Kingdom wit h a confirmed diagnosis of acquired MG and 510 cats with other neuromuscula r disorders, including generalized weakness, megaesophagus, and dysphagia ( control group). Procedures-Records were retrieved from a database containing results of ser um samples tested for acetylcholine receptor antibodies. Signalment, includ ing breed, age, and slate or country of origin, month of onset, and initial clinical signs were obtained. An acetylcholine receptor antibody titer > 0 .3 nmol/L was diagnostic for acquired MG. Unconditional logistic regression was used for statistical analysis. Results-Compared with mixed-breed cats, the breed with the highest relative risk of acquired MG was the Abyssinian (including Somali). Significant dif ferences between sexes were not detected. There was no compelling evidence for a difference in risk of developing MG between slates or countries. Rela tive risk increased after 3 years of age. The most common clinical signs we re generalized weakness without megaesophagus and weakness associated with a cranial mediastinal mass. Focal signs, including megaesophagus and dyspha gia without signs of generalized weakness, were also evident. Conclusions and Clinical Relevance-A breed pre disposition for acquired MG in Abyssinians (and related Somalis) was observed. Clinical signs were vari able and included generalized weakness, mega esophagus, and dysphagia, A cr anial mediastinal mass was commonly associated with MG in cats.