Have you had your HLA-B27 tested? That genetic marker is positive in a lot of people with seronegative spondyloarthropathies (my brain hurts from spelling that) and can help diagnose either Ankylosing Spondlytitis, Psoriatic Arthritis or Undifferentiated Spondylitis. They are a collection of autoimmune arthritis-es that have symptoms that flare in the spine.

I have Psoriatic Arthritis that is symmetrical (both sides, small joints in the fingers and toes, wrists and ankles) AS WELL AS in my spine. Specifically my neck will 'pop' and all of a sudden I can't move it for several days and take high doses of muscle relaxers to calm it down. The inflammation between the spine joints (gah - what are they called?) shows up on films and accounts for that symptom according to my rheumatologist.

I had read somewhere in my search for why I would have neuropathy with Psoriatic Arthritis (so far I've got nothing) I did come across something that said there was a strong association between Ankylosing Spondylitis and Neuropathy - but I can't recall where I saw that. Don't trust me - google search it and see what you can come up with.

Also - even though you don't have psoriasis now, it doesn't mean you don't have Psoriatic Arthritis. Sometimes the arthritis shows up first. Clues to it being PsA would be inflammation in the joints closer to the fingertips rather than the knuckles which is more common in RA.