CLINICAL FORMS OF ACQUIRED MYASTHENIA-GRAVIS IN DOGS - 25 CASES (1988-1995)

The purpose of this project was to investigate the clinical forms of a cquired myasthenia gravis in dogs. The medical records from 25 dogs wi th seropositive acquired myasthenia gravis were reviewed, and the foll owing data were recorded for each patient: signalment, history, clinic al findings; results of IV edrophonium chloride administration, repeti tive nerve stimulation, and presence or absence of muscle membrane sta ining by immunocytochemical methods; serum acetylcholine receptor anti body concentration; treatment; and outcome. Several clinical forms of acquired myasthenia gravis were identified. Nine of the 25 patients (3 6%) had no historical or clinical evidence of appendicular muscle weak ness, and were designated as focal myasthenics. These dogs exhibited f ocal weakness in one or more of the following muscle groups: facial (3 of 9), pharyngeal (3 of 9), and laryngeal (3 of 9). The remaining 16 dogs (64%) exhibited appendicular muscle weakness. Four of these 16 do gs had acute onset and rapid development of clinical signs, and were d esignated as acute fulminating myasthenics. The remaining 12 dogs were classified as generalized myasthenics. All 4 dogs with acute fulminat ing myasthenia gravis had megaesophagus, 2 had facial muscle weakness, and 1 had pharyngeal muscle weakness. Ten of the 12 dogs with general ized myasthenia gravis had megaesophagus, 4 had facial muscle weakness , 4 had pharyngeal muscle weakness, and 3 had laryngeal muscle weaknes s. Historical or clinical evidence of exercise-associated appendicular weakness was found in only 6 of the 12 (50%) dogs with generalized my asthenia gravis, and in none of the dogs with acute fulminating myasth enia gravis. Seven of the 12 dogs with generalized myasthenia gravis h ad weakness primarily (n = 1) or exclusively (n = 6) of the pelvic lim bs. Two of the 4 dogs with acute fulminating myasthenia gravis had pri marily pelvic limb weakness. Twelve of the 25 dogs (48%) died or were euthanized shortly after admission to the hospital due to aspiration p neumonia. The dogs with acute fulminating myasthenia gravis had a mark edly higher 1-year mortality rate in comparison with the other 2 group s. The use of immunosuppressive therapy had a significant positive eff ect on patient survival, regardless of the type of myasthenia gravis. This investigation demonstrates that acquired myasthenia gravis in dog s is a disorder with a wide spectrum of clinical forms, similar to the analagous disorder in people.