Is it likely that i have ms if my spinal tap is completely negative?

Possible: Each test has a false negative and false positive rate. Some better than others. While you may be able to diagnose MS by spinal tab, that is usually positive a little more than 80% of the time. This means some who do have it might test negative. A brain MRI is positive in more than 95% of cases. If you are still having symptoms of ms, see your doctor to consider an mri.

Possibly: A negative spinal tap is usually a good sign in terms of ruling out ms, but it's not the only sign, and it depends on the tests performed on the spinal fluid. A negative brain MRI is more supportive of a negative evaluation, as is the absence of certain proteins that are often found in spinal fluid of MS patients. I would talk to your doctor about a MRI and about these proteins in the fluid.

Is possible: If you have MRI lesions which are c/w MS, but spinal fluid is normal, that would indicate a far better prognosis. Spinal fluid is helpful in 95% of cases, but that leaves a small number of equivocal situations. We try to resolve by follow-up MRI's, seeking whether changes are occurring. Chances are, that you probably do NOT have MS.