Objective—To determine prevalence of initial clinical
signs and risk factors for acquired myasthenia gravis
(MG) in cats.
Design—Retrospective case-control study.
Animals—105 cats from the United States, Canada,
and the United Kingdom with a confirmed diagnosis
of acquired MG and 510 cats with other neuromuscular
disorders, including generalized weakness,
megaesophagus, and dysphagia (control group).
Procedures—Records were retrieved from a database
containing results of serum samples tested for
acetylcholine receptor antibodies. Signalment, including
breed, age, and state 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 differences
between sexes were not detected. There
was no compelling evidence for a difference in risk of
developing MG between states or countries. Relative
risk increased after 3 years of age. The most common
clinical signs were generalized weakness without
megaesophagus and weakness associated with a cranial
mediastinal mass. Focal signs, including megaesophagus
and dysphagia without signs of generalized
weakness, were also evident.
Conclusions and Clinical Relevance—A breed predisposition
for acquired MG in Abyssinians (and related
Somalis) was observed. Clinical signs were variable
and included generalized weakness, megaesophagus,
and dysphagia. A cranial mediastinal
mass was commonly associated with MG in cats. ( J
Am Vet Med Assoc 2000;216:55–57)