MS Society of Canada - Calgary Chapter

How is MS diagnosed?

Page 7

MS is not always easy to diagnose because symptoms may come and go. In addition, other diseases of the CNS have some of the same symptoms. No single neurological or laboratory test can confirm or rule out MS.
Some people have symptoms that are very difficult for physicians to interpret, and these people must “wait and see.”

The long-established criteria for diagnosing MS are:

There must be objective evidence of two attacks . (i.e. two episodes of demyelination in the CNS). An attack, also known as an exacerbation, flare-up, or relapse, is defined clinically as the sudden appearance or worsening of an MS symptom or symptoms, which lasts at least 24 hours. The objective evidence comes from findings on the neurological exam and additional tests.
The two attacks must be separated in time (at least one month apart) and space (indicated by evidence of inflammation and/or damage in different areas of the CNS).
There must be no other explanation for these attacks or the symptoms the person is experiencing.

Tests such as magnetic resonance imaging, (MRI)examination of cerebrospinal fluid, and evoked response testing have played an increasingly important role in the diagnostic process. In 2001, the International Panel on the Diagnosis of Multiple Sclerosis, chaired by W.I. McDonald, FRCP (Royal College of Physicians, London), issued a revised set of diagnostic criteria (Annals of Neurology 2001; 50:121-127).

In addition to the traditional requirements, the revision provides specific guidelines for using findings on MRI, cerebrospinal fluid analysis, and visual evoked potentials to provide evidence of the second attack and thereby confirm the diagnosis more quickly. These guidelines also facilitate the diagnostic process in those patients who have had steady progression of disability without distinct attacks.

MRI (magnetic resonance imaging) is the preferred method of imaging the brain to detect the presence of plaques or scarring caused by MS. This technology is able to detect lesions in different parts of the CNS and differentiate old lesions from those that are new or active.

Still, the diagnosis of MS cannot be made solely on the basis of MRI. There are other diseases that cause lesion areas of damage in the brain that can look like MS. There are also spots found in healthy individuals, particularly in older persons, which are not related to any ongoing disease process.

On the other hand, a normal MRI cannot rule out a diagnosis of MS. About 5% of patients who are confirmed to have MS on the basis of other criteria, do not show any lesions in the brain on MRI. These people may have lesions in the spinal cord or may have lesions that cannot be detected by MRI. Eventually, however, the vast majority of people with MS will have brain and/or spinal lesions on MRI. The longer the MRI remains negative, the more questionable the diagnosis becomes. If the MRI findings continue to be negative more than a year or two after the initial diagnosis is made, every effort should be made to identify another possible cause for the symptoms.