Exercise-induced collapse in young, otherwise healthy, Labrador retrievers is an uncommon, dramatic, self-limiting condition. The exact underlying metabolic or genetic basis for the syndrome has not been determined.

In this multicenter study involving three countries, 14 Labrador retrievers with a presumptive diagnosis of exercise-induced collapse were evaluated and compared with 14 normal Labrador retrievers by using clinicopathologic data and strenuous exercise testing protocols. Affected dogs were a mean of nearly 2 years of age and had experienced at least three episodes of exercise-induced weakness or collapse. Ten of 14 dogs with exercise-induced collapse had an abnormal gait during exercise; these dogs were more tachycardic and had a more severe respiratory alkalosis after exercise compared with normal dogs. All of the dogs with exercise-induced collapse had progressive deterioration within two minutes of stopping the exercise.

Muscle biopsy results and lactate and pyruvate concentrations were normal in affected dogs. The affected dogs' body temperatures were similar to that of normal dogs participating in the same exercises, and mentation was not altered. Genetic analysis excluded malignant hyperthermia as a cause of exercise-induced collapse, although the authors provided an addendum describing a possible causal genetic mutation for exercise-induced collapse.¹ Six of the 14 affected dogs were adopted into homes where they do not participate in triggering activities, and five of the six never experienced collapse again. None of the dogs developed a progressive systemic or neurologic disease.

This report provides useful clinical information for an uncommon but potentially serious condition in young, seemingly healthy Labrador retrievers that suddenly develop exercise intolerance. Because of the breed popularity and the active lifestyle of the dogs and their owners, practitioners, clients, and breeders should be aware of the condition. Furthermore, practitioners are alerted that this idiopathic, self-limiting condition may have a genetic component. In addition, if owners limit the exercise trigger, dogs may have reduced episodes of collapse and live a relatively normal life. While the exact cause of the exercise-associated collapse is unknown, an increased awareness and opportunities for genetic testing may help delineate the heritable nature of the condition, as the authors suggested.

REFERENCE

1. Patterson EE, Minor KM, Tchernatynskaia AV, et al. A canine DNM1 mutation is highly associated with the syndrome of exercise-induced collapse. Nat Genet 2008;40(10):1235-1239.

Taylor SM, Shmon CL, Adams VJ, et al. Evaluations of labrador retrievers with exercise-induced collapse, including response to a standardized strenuous exercise protocol. J Am Anim Hosp Assoc 2009;45(1):3-13.

Joseph Harari, MS, DVM, DACVS