Intermittent weakness in four Labrador Retrievers

A series of different conditions in Labrador Retrievers may lead to episodic gait abnormalities, muscular weakness, muscle stiffness or even collapse. Examples are exercise-induced collapse (EIC) caused by a mutation in the Dynamin 1 gene or as an atypical form without mutation, and central nuclear myopathy (CNM), caused by a genetic mutation in the protein tyrosine phosphatase-like protein A. This case series report presents four Labrador Retrievers with episodic weakness or stiffness not affected by any of these three diseases. The general and neurological examinations of all four patients were normal. The results of a complete blood count (CBC) and blood chemistry analysis were within normal limits, too. Exercise did not cause any remarkable changes in blood chemistry. Genetic testing for EIC and CNM was negative in all four animals and an electrodiagnostic examination did not reveal any pathological findings. Muscle biopsies, however, showed mild acute to chronic myopathic changes such as myofiber atrophy and hypertrophy. These cases emphasise the fact that different diseases in Labrador Retrievers may lead to episodic weakness, collapse or spasticity, which are not caused by the mutations mentioned above. Further investigations are required to clarify as to whether these cases have a common underlying cause (such as an ion channelopathy) or whether various aetiologies have converged to give a similar clinical phenotype.