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

G. Diane Shelton DVM, PhD, DACVIM1, Mindy Ho BS2, and Philip H. Kass DVM, PhD, DACVPM3
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  • 1 Comparative Neuromuscular Laboratory, Department of Pathology, School of Medicine, University of California-San Diego, La Jolla, CA 92093-0612.
  • | 2 Comparative Neuromuscular Laboratory, Department of Pathology, School of Medicine, University of California-San Diego, La Jolla, CA 92093-0612.
  • | 3 Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, CA 95616-8734.

Abstract

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)

Abstract

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)