How Multiple Sclerosis Is Diagnosed


There is no one specific test that can be performed to make the diagnosis of multiple sclerosis (MS). For this reason, MS often goes undiagnosed or it may take many years before a physician is able to make a definitive diagnosis.

A physician is likely to suspect MS when neurological symptoms, physical examination and medical history suggest the disorder. The diagnosis of MS is often made by exclusion, meaning that other diseases are ruled out first.

Imaging tests such as magnetic resonance imaging (MRI) when performed using a contrast agent, can locate lesions in the central nervous system that have developed as a result of myelin loss. This test can help to distinguish new lesions from old ones and may be helpful in plotting the progression of MS. An MRI of the brain is abnormal in nearly 90 percent of people with definitive MS.

Evoked potential testing looks at the speed and efficiency of myelin conduction. It is also helpful in detecting myelin lesions.

A spinal tap or lumbar puncture may be advised so that a sample of cerebral spinal fluid can be analyzed. Patients with MS often have cerebral spinal fluid that contains elevations in IgG (a partial protein) which indicates an abnormality in the immune system.

To make a definitive diagnosis of MS, the physician must confirm:

  • Plaques of lesions in at least two distinct areas of the central nervous system white matter
  • Evidence that the plaques have occurred at different points in time or have occurred progressively over six months’ time
  • That the plaques found in the white matter have no other possible explanation (meaning all other related diseases have been ruled out)

Diagnostic categories for multiple sclerosis

Definitive MS. Consistent course (relapsing-remitting course with at least two bouts separated by at least one month, or slow or stepwise progression for at least six months); documented neurological lesions in more than one site of brain or spinal cord white matter; onset of symptoms between ages 10 and 50 years of age, with the absence of other more likely explanation of neurological symptoms.

Probable MS. History of relapsing-remitting symptoms; signs not documented and only one current sign commonly associated with MS; documented single bout of symptoms with signs of more than one white matter lesion; good recovery, then variable symptoms and signs; absence of other more likely neurological explanations.

Possible MS. History of relapsing-remitting symptoms; no documentation of signs establishing more than one white matter lesion; absence of a more likely neurological explanation.

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