This question (and answer) deserves some attention and explanation. Since MS means multiple areas of damage (sclerosis literally means scarring or hardening), there are two basic rules for diagnosing MS:
- The person must have had at least two relapses (an episode where symptoms were present), separated by at least one month and
- There must be more than one lesion on the brain or spinal cord.
The intelligent person who sent me this question talked about having an attack and how agonizing it was to wait for the second “confirmatory” relapse to determine whether he definitely had MS.
Even if you had several relapses, these often go undiagnosed (or misdiagnosed), and multiple relapses don’t automatically lead to a diagnosis of MS. In my case, when I was finally diagnosed, my neurologist said that I probably had MS for 15 to 20 years. Once this was explained, I could recall several medical “incidences” and strange symptoms that were actually probable relapses.
The fairly recent widespread availability of MRI scans, however, have allowed huge progress in diagnosing MS. Some of the former shortcomings of the previous diagnostic criteria (namely waiting for often vague and transient symptoms to indicate multiple relapses) have been addressed in the McDonald criteria, a set of standards published in 2001 (and revised in 2005) that incorporates the use of MRI scans. Basically, these criteria state that in the case of only one relapse, MS can be confirmed by:
- Dissemination in space by two or more MRI lesions consistent with MS and
- Dissemination in time by MRI or 2nd attack
While this sounds very similar to the above “rules” for diagnosing MS, there is one very important change: “dissemination in time by MRI” means that if a person only has one attack and there is a lesion (or more than one lesion) on an MRI, a second MRI can be performed three months later. If a new lesion appears, this can be used to diagnose MS, without waiting for a second clinical relapse. The revised criteria also allow a new T2 lesion appearing any time 30 days after the initial event to qualify as "dissemination in time." They also include spinal cord lesions as well as brain lesions as MRI markers to confirm MS diagnosis.
Note: New lesions or "active lesions" are known as gadolinium-enhanced lesions, as they show up as very bright on the MRI scan in the presence of gadolinium (the contrast agent used during MRIs). Interestingly, lesions will only react with gadolinium for about six weeks, so any gadolinium-enhanced lesions found after three months will be new.
Read related articles:
McDonald WI, Compston A, Edan G, Goodkin D, Hartung HP, Lublin FD, McFarland HF, Paty DW, Polman CH, Reingold SC, Sandberg-Wollheim M, Sibley W, Thompson A, van den Noort S, Weinshenker BY, Wolinsky JS. Recommended diagnostic criteria for multiple sclerosis: guidelines from the International Panel on the diagnosis of multiple sclerosis. Ann Neurol. 2001 Jul;50(1):121-7.
Polman CH, Reingold SC, Edan G, Filippi M, Hartung HP, Kappos L, Lublin FD, Metz LM, McFarland HF, O'Connor PW, Sandberg-Wollheim M, Thompson AJ, Weinshenker BG, Wolinsky JS. Diagnostic criteria for multiple sclerosis: 2005 revisions to the "McDonald Criteria". Ann Neurol. 2005 Dec;58(6):840-6.