Your diagnosis of multiple sclerosis may have been made using the McDonald criteria. This is a tool for clinicians to ensure that they provide an accurate diagnosis of MS as early as possible, and guide them to the tests they should arrange for you in order to be sure.
The first set of criteria were published in 2001 by a team led by Prof Ian McDonald. They have been extensively revised several times, most recently in 2017. The revisions are made by a panel of MS experts who look at the most up-to-date research on how MS appears and progresses in patients.
The newest revisions will not change your diagnosis of MS, but they may allow a doctor to give a diagnosis of MS to someone earlier in their own disease course. This could mean that a patient gets access to the right treatment sooner.
The key requirement for a diagnosis of MS is evidence of damage to the central nervous system that is disseminated in time and space. This means showing that damage has occurred at different dates (Dissemination in time, or DIT) and to different parts (Dissemination in space, or DIS) of the central nervous system. This distinguishes MS from other neurological conditions.
The McDonald criteria use MRI evidence extensively and suggest that an MRI scan is made for everyone in whom an MS diagnosis is possible. Lesions may be found even in someone with few or no clinical symptoms, which would be evidence for DIS.
The presence of oligoclonal bands in the spinal fluid is also a good marker for MS. It shows that there has been disease activity in the past, and so can be used as evidence of DIT.
So, if you visit your doctor with a neurological symptom that suggests a potential first MS event (CIS), you could therefore have an MRI scan and lumbar puncture. If these tests show lesions in the central nervous system and oligoclonal bands in your spinal fluid, a diagnosis of MS could be made immediately. You would not need to wait for another attack or relapse before starting treatment.
A diagnosis of MS is most secure if there is more than one kind of evidence. Misdiagnosing MS could put patients at risk from the side-effects of MS drugs unnecessarily. Clinicians still need to use their judgement, particularly when diagnosing MS in children or population groups where MS is uncommon.