In a patient with a relapsing-remitting presentation of MS, DIS can be demonstrated through either:

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Objective, clinical evidence of ≥2 lesions or
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≥ 1 symptomatic or asymptomatic MS-typical T2 lesions in 2 or more areas of the CNS: periventricular, juxtacortical/cortical, infratentorial, or the spinal cord.

DIT can be demonstrated through either:

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≥ 2 typical MS attacks separated by a period of remission,
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The simultaneous presence of both enhancing and non-enhancing symptomatic or asymptomatic MS-typical MRI lesions,
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A new T2-enhancing MRI lesion compared to a baseline scan, or
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The presence of CSF-specific oligoclonal bands.

If, however, a patient initially presents with a continual progression of disability, MS can still be diagnosed if they have had at least 1 year of disability progression and two of the following:

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≥ 1 symptomatic or asymptomatic MS typical T2 lesions (periventricular, juxtacortical/cortical, or infratentorial),
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≥ 2 T2 spinal cord lesions, or

The presence of CSF-specific oligoclonal bands.

An MRI of the brain and spinal cord is extremely important in the diagnosis of MS as it is very sensitive in detecting white matter abnormalities. To diagnose MS there should be at least one typical MS lesion in at least two areas that are characteristic of MS. A typical MS lesion is a focal hyperintensity on a T2 weighted sequence, round/ovoid in shape, ranges from a few millimeters to 1–2 cm in size, and is at least 3 mm in its long axis. Characteristic locations include periventricular (in direct contact with the lateral ventricles, without intervening normal white matter), juxtacortical/cortical (in direct contact with the cortex, without intervening normal white matter), infratentorial (in the brainstem, cerebellar peduncles, or cerebellum), or anywhere in the spinal cord (the cervical cord is the most frequently involved). Another feature characteristic of MS lesions is gadolinium enhancement. Gadolinium enhancement is seen in acute MS lesions and is transient, usually lasting 4 weeks or less. This feature can help support the DIT criteria of diagnosis, as the presence of gadolinium-enhancing and nonenhancing lesions confirms the presence of new and chronic lesions.