Unfortunately, Lyne isn't that easy to catch. That's one of the reasons I believe I'm in this boat. The testing is inaccurate and the controversy over the disease has gotten very politicized. I tested negative 7 times over the years. I believe I was bitten 2007 of earlier, but it's hard to say.
Unfortunately, the spinal tap may not be definitive either. I've had two... Neither led to my diagnosis of Lyme. I found a savvy infectious disease doc who knew how inaccurate the tests are, and started me on antibiotics. It wasn't until then that I knew I was on the right track.
And honestly, I'm not big on putting stuff in my body either. To me, antibiotics were a better choice than the current choices for MS. I strongly suggest joining a few other groups online if you have the time, Yahoo offers some great Lyme forums and MS have a great site called This is MS. There are a bunch of supportive folks out there who can help guide you throu this process. Finding a doc to give you antibiotics will be a challenge. According to the CDC, late stage Lyme is rare. Docs follow that, and will dismiss you quicker than not. I had to find my specialist through one of the Lyme support groups on Yahoo.
I do caution you in this regard though.. Trust your gut. People on both sides of the Lyme/MS club tend to sway you in one direction or another. These past three years have been nothing short of a roller coaster ride for me between these two diagnosises. But you'll make it through.. The beginning is the scariest, so make sure you have a good support system. And if you don't, try to find one online.
I had a similar experience over the last few years. Diagnosed with MS, but not really fitting into that diagnosis for a number of reasons. I searched for answers, eventually learning of Lyme after several others in my family were diagnosed (we live in Lyme-endemic upstate NY. I found a specialist who treats Lyme people almost exclusively. Extremely knowledgable doc. I've been doing well on antibiotics, and have steered away from the MS drugs. At his suggestion, I followed up with a Neuro just to be on the safe side. I had opted out of treatment for a few months to give my body a break. At the Neuros recommendation, I had an MRI which showed new lesions on my spine. According to my Lyme doc, this doesn't happen with Lyme disease. His belief is I have Lyme induced MS. And while this will be my lot in life, I know in my gut the antibiotics are helping to keep me on the right track.
If you have Lyme as an underlying condition, and have had it for a long time, I think the body gets to a point when it simply can't distinguish between good and bad and starts to launch the attacks. That's where the antibiotics come in handy. After 3 years, I'm no worse for wear than I was when I was first diagnosed. I've radically changed everything I do though, just to make sure I'm as healthy as a person can be. I would strongly encourage you to join a Lyme group to find a Lyme-literate MD in your area. You may have to travel (most do), but it may prove to be beneficial in the long run.
There is also a group at Vanderbilt University who have some compelling research that lends to another infection (CPN) as a causative factor in many MS diagnosed patients. There protocol is similar to the Lyme treatments.
I also want to point out that this is a confusing disease. There are so many issues that are yet to be explained. I never bought into my body attacking itself for no reason. I believe there's an underlying issue causing the MS. I'm not alone in is thought either; there's a large subset that believe the same.