First, a thorough orthopedic exam and neurologic exam must be performed. All four legs should be examined, checking joints, range of motion, flexibility, palpating the muscles and checking ligaments to confirm integrity. Any orthopedic abnormalities should be noted, but not assumed to be the source of the limping. Then the neurologic exam starts. You, as the ever observant owner, will be asked whether or not your dog drags his feet when he walks. You may hear his nails scuffing on the sidewalk. The vet may find scuff marks or worn nails, sometimes even small abrasions on top of the feet. You will be asked about your pet's "bathroom" habits. You may notice that your dog seems to "get the message too late" that he needs to go potty. He may have accidents in the house when he is not even aware that he is having a bowel movement. Your dog may have balance problems or seem to fall easily. His walk might be described as that of a drunken sailor's, meaning he staggers a bit and has trouble walking in a straight line, perhaps even tripping over his own feet. Sometimes your dog may "scissor" in the rear legs. This means that one rear foot crosses in front of the other. Oftentimes, the rear legs are the only ones involved or, if all four feet are involved, the back legs are worse. Eventually, you may notice that your dog's leg muscles are getting smaller.
Your family vet, vet neurologist, or rehab vet should check reflexes, palpate the spine, and perform other special nerve tests, depending on which legs are affected. All dogs with syuspected neurologic issues will have conscious proprioception tested. This is a quick test where your dog's feet, one at a time, are placed into an abnormal position (standing on the top of the paw instead of the bottom) to see how long it takes for your dog to "get the message" and correct the position.(Hint: normal is less than 2 seconds!) Perhaps your dog's response is delayed slightly or so severe he never corrects the position himself! From there, any special testing that seems indicated should be done. This could include x-rays, blood work, DNA testing for Degenerative Myleopathy, spinal taps, or an MRI.
Even without avanced testing or an exact diagnosis, many times we can say with certainty that the nervous system is involved. Any diagnosis of neurological issues may interfere with your dog's function. That means your dog should start physical rehabilitation. Progression of the disease can be slowed or even stopped in some cases and we can work to start rebuilding strength and retraining neuromuscular efficiency.