My Husband Has Been Having Difficulty Walking And Also With

My husband has been having difficulty walking and also with speech, he tends to slur his words or has difficulty getting them out. He has had many tests and many things have been ruled out by General physicians, neurologists and neurosurgeons. He had surgery last December to repair vertebrae in his cervical spine that had been compressing the nerves. He recently had contrasting and non contrasting MRI's of cervical spine and brain. Brain is clear of any abnormality and cervical spine showed surgery went well and there is no compression. However, he is experiencing what physical therapist calls proprioception and has difficulty walking and slurs his words, he also gets severe leg cramps, has difficulty going down stairs and is just generally awkward. He has been tested for many obvious neurological disorders, as well as things like lymes disease and std's. Everything comes back negative. We are stumped and need a new direction to go in. Any advice? Karen Haynie