DU pet people: I need your help. My cat is very ill; my vet is clueless.

[iconoclastic cat]

Okay, everyone, I need your help. I need to figure out what is wrong with my cat.

Here's the story:

Around the end of
January, Zooey (our cat) started walking very stiffly.
Within a three days she was just pacing the condo
restlessly, still very stiff and uncoordinated. The
vet put her on antibiotics, but she just got worse
over the next two days. We brought her in for x-rays,
but nothing showed up. Blood work showed nothing,
either. The vet put her on steriods, and she was back
to normal within a day. She stayed on the steroids for
a week and a half, but when I eased the dose down to
half of what it was (as per the instruction from my
vet), she totally relapsed in two days. She paced for
a day, stumbled like a drunk for another day, and we
brought her in the next.

The vet is baffled. Zooey was pumped full of fluids
and steroids for three days in the vet's kennel, and
when I went to pick her up, it was like nothing had
happened to her. The vet said that we'd just keep her
on steroids for a couple months, but I keep reading
that that much steroid use can do a lot of harm, too.
I'm going to try to find an answer. I'm afraid that
this may not have a happy ending, either.

Thanks, and if you know anything about this, please
let me know.

By the way, if knowing exact dates, medication, etc. could help, let me know and I'll post it.

Also: If you know anyone who might know what's going on, DUmail me.

Yes, by the way, I have posted this elsewhere.