A Novel Movement Disorder in Related Male Labrador Retrievers Characterized by Extreme Generalized Muscular Stiffness

Abstract

Objectives: To describe the clinical phenotype of a new motor disorder in Labrador Retrievers. Animals and Methods: Case series study. Seven young male Labrador Retrievers presented for evaluation of stiff gait. Results: All affected dogs had generalized muscular stiffness, persistent at rest and resulting in restricted joint movements. They showed a forward flexed posture, festinating gait, and bradykinesia. Signs developed between 2 and 16 months of age and tended to stabilize in adulthood. Needle electromyogram in the conscious state showed continuous motor unit activity in resting epaxial and proximal limb muscles. This activity was abolished by general anesthesia. Muscle and nerve histopathology was normal. In 2 dogs necropsied, astrocytosis was evident throughout the spinal cord gray matter, reticular formation and caudate nuclei. Decreased neuronal counts were selectively found in the spinal cord Rexed's lamina VII, but not in VIII and IX. Pedigree analysis showed that the affected dogs were from 5 related litters.Conclusions and Clinical Importance: This new hypertonicity syndrome in Labrador Retrievers is unique because of the selective distribution of the histological lesions, the lack of progression in adulthood, and its exclusive occurrence in male dogs. Pedigree analysis suggests an X-linked hereditary disease, although other modes of inheritance cannot be ruled out with certainty. We hypothesize that altered output from basal nuclei and reticular formation together with motor neuron disinhibition caused by a decreased number of spinal cord interneurons leads to the muscular stiffness.

A cross-species approach to disorders affecting brain and behaviour

“…Canine dyskinesias are primarily breed-associated disorders [65][66][67][68][69] ( Table 2) with signs that can be paroxysmal or constant (such as hypertonicity syndrome in Labrador retrievers) 66,69 . Causes of dyskinesias include degenerative or acquired disorders of the basal nuclei and upper brainstem (such as in Parkinson disease and Sydenham chorea in humans), suspected serotonin deficiencies within the spinal cord (such as in Scottish terrier cramps) and skeletal muscle ion channel abnormalities (such as in myotonia congenita) 65,67,68,70,71 . Examples of parallels between human and canine patients include orthostatic tremors in Great Danes that resemble primary orthostatic tremor in humans and dyskinesias in Jack Russell terriers and Labradors that mirror non-paroxysmal dyskinesias in humans.…”

Dystonia and Paroxysmal Dyskinesias: Under-Recognized Movement Disorders in Domestic Animals? A Comparison with Human Dystonia/Paroxysmal Dyskinesias

“…Not all motor dysfunctions in animals can be correlated to a specific human movement disorder. An example of this would be the inherited hypertonicity syndrome of Labrador Retrievers described by Vanhaesebrouck et al ( 33 ), which is associated with a selective loss of spinal cord interneurons. As summarized in Table 3 , different episodic neurological signs can occur in dogs and should be separated from paroxysmal dyskinesias.…”

Extreme generalised muscular stiffness in young labrador retrievers

“…A NOVEL movement disorder characterised by extreme generalised stiffness has recently been recognised in related labrador retrievers in the UK (Vanhaesebrouck and others 2011). This disease appears to be emerging, since new cases continue to be diagnosed.…”