Diagnosis of MS has always been a clinical decision, but many tests and criteria have assisted the clinician in arriving at conclusions. Tests such as MRI, the examination of the cerebrospinal fluid (CSF), and visual evoked potentials (VEP) are helpful in confirming the clinical suspicion of MS.

The clinician first conducts a history of the features of the patient’s story of neurological symptoms, and then a neurological examination to assess how the nervous system has been affected. Defined criteria are used to conclude whether the features fulfil the clinical diagnosis. Tests then help confirm the suspicion that the disease is or is not present. Having defined criteria for the clinical diagnosis and criteria for a positive MRI for MS allow for more precision in the diagnosis and lessen the likelihood of a premature diagnosis in questionable cases where the MS-like symptoms may be due to some other condition. Just as with other aspects of the disease, we learn more as the criteria are adjusted and improved. The McDonald Criteria are currently being used to incorporate the clinical understanding and add helpful tests such as MRI, CSF examination, and visual evoked potentials.

Although the MRI is a relatively new test in the last few decades, it is of great diagnostic assistance to the clinician. It is valuable in revealing much about the activity of the disease, helpful in assessing potentially effective drugs, and useful as part of the evaluation of the impact of new therapies. As we become aware of the variety of presentations and courses of MS, we are able to diagnose cases that would have been undiagnosed in the past, or would have gone on for many years without a diagnosis.