Hindleg lameness when runningWhen hunting my 2 1/2 year old Lab, he sometimes loses control and use of his rear legs. He actually runs dragging his rear since his back legs don't want to work. It seems to happen only when he is quartering the field, it does not happen in retriever training or dove hunting or duck hunting. If I notice this starting, I can make him rest for 15 - 20 minutes and resume hunting. It does not appear to hurt him but certainly loses the use of his rear legs. I have stopped when this situation occurs and immediately taken him to the vet, but when I take him out of his crate at the vet he is 'cured', and shows no sign of any problem. The dog OFA'd Good and the vet could find no problem when he x-rayed his spine. Two possibilities come to mind. If the muscle weakness occurs within a few minutes of exercise I would have your vet rule out a disease called Myasthenia Gravis which can cause signs of weakness. Another I think more probable cause is a syndrome in labs called "Labrador myopathy" or "exercise-induced myopathy". In contrast to Myasthenia, weakness occurs later in exercise and after a short rest (like a car ride to the vet) the dog seems fine. This syndrome is a rascal to diagnose, have your vet draw blood pre and post exercise to measure a thing called plasma lactate and pyruvate and send them to Dr. Diane Sheltons neuromuscular lab in LaJolla,California. I don't know of any treatment for this myopathy except not to exercise the dog excessively. The condition is most likely inherited, not progressive and the dogs live a normal life. Good luck, tell your vet I'm glad it's his/her case!
NOTE: Also check out : http://medicine.ucsd.edu/vet_neuromuscular/cases/2000/jun00.html
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