Clinical features and outcome of acquired myasthenia gravis in 94 dogs

Abstract

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.

Keywords: acetylcholine; autoimmune; comorbidity; junctionopathy; prognosis; remission.

FIGURE 1

Age in relation to clinical group of myasthenia gravis. The distribution of ages in each clinical group is shown, the ends of the box representing the upper and lower quartiles; median age is marked by the vertical line inside the box. The length of whiskers represents either 1.5 times the interquartile range, or the range from minimum to maximum, whichever is shorter. Younger animals were more likely to be represented in the clinical remission group compared to the no clinical improvement group

FIGURE 2

Duration of follow‐up in relation to clinical group of myasthenia gravis. The distribution of follow‐up durations in each clinical group is shown, the ends of the box representing the upper and lower quartiles; median age is marked by the vertical line inside the box. The length of whiskers represents either 1.5 times the interquartile range, or the range from minimum to maximum, whichever is shorter. Follow‐up time is represented by a logarithmic x axis for clarity. Dogs that were euthanized or died are represented by ; those lost to follow‐up are represented by white dots

FIGURE 3

Distribution of presenting clinical signs and comorbidities with clinical group of myasthenia gravis. The clinical scoring groups are organized by colored bars, shaded areas below the bars representing the cases within that group with the corresponding presenting clinical signs (upper rows) or comorbidities (lower rows). dz, disease

FIGURE 4

Baseline acetylcholine receptor antibody concentration in relation to clinical group of myasthenia gravis. The distribution of AChR Ab concentrations in each clinical group is shown, the ends of the box representing the upper and lower quartiles; the median AChR Ab concentration is marked by the vertical line inside the box. The length of whiskers represents either 1.5 times the interquartile range, or the range from minimum to maximum, whichever is shorter. The no clinical improvement group had higher baseline AChR Ab concentrations than the clinical remission group. Ab, antibody; AChR, acetylcholine receptor

FIGURE 5

Baseline and follow‐up acetylcholine receptor antibody concentrations in individual dogs across the clinical groups of myasthenia gravis. Each line represents the baseline and follow‐up AChR Ab concentration for dogs within the respective groups. The dotted line represents the upper reference limit of AChR Ab concentration (0.6 nmol/L). Ab, antibody; AChR, acetylcholine receptor