My Doberman is nearly 4 years old. Over the last few months he has started having hind issues, where his hind goes down and he has trouble lifting his legs when climbing steps. His hind legs go under his stomach and occasionally his hind legs shake and have given out. He has had extensive X-Rays, blood work and an MRI. No issues were revealed. We were able to rule out wobblers, hip dysplasia and other common Doberman health issues. He has just started a two week steroid program. He has gone from a very active life style to little or no exercise. The neurologist we went to see is just as baffled as we are. She is recommending a spinal tap and a nerve biopsy, but we are skeptical of that. Has anyone encountered something similar to this, or can point us in the right direction?