Definitions

Attack

Attack, relapse, exacerbation, and (when it is the first episode) clinically isolated syndrome are synonyms.

Clinically isolated syndrome

A monophasic clinical episode with patient-reported symptoms and objective findings reflecting a focal or multifocal inflammatory demyelinating event in the CNS, developing acutely or subacutely, with a duration of at least 24 h, with or without recovery, and in the absence of fever or infection; similar to a typical multiple sclerosis relapse (attack and exacerbation) but in a patient not known to have multiple sclerosis. Thus, if the patient is subsequently diagnosed with multiple sclerosis (by fulfilling dissemination in space and time, and ruling out other diagnoses), the clinically isolated syndrome was that patient’s first attack. A clinically isolated syndrome can be monofocal (reflecting pathology in a single location) or multifocal; the specific manifestations of a clinically isolated syndrome depend on the anatomical location (or locations) of the pathology. Typical presentations include unilateral optic neuritis, focal supratentorial syndrome, focal brainstem or cerebellar syndrome, or partial myelopathy; examples of atypical presentations include bilateral optic neuritis, complete ophthalmoplegia, complete myelopathy, encephalopathy, headache, alteration of consciousness, meningismus, or isolated fatigue.

Lesion

An area of hyperintensity on a T2-weighted or proton-densityweighted MRI scan that is at least 3 mm in long axis.

Dissemination in space

The development of lesions in distinct anatomical locations within the CNS—ie, indicating a multifocal CNS process.

Dissemination in time

The development or appearance of new CNS lesions over time.

Cortical MRI lesions

Lesions within the cerebral cortex. Typically, special MRI techniques such as double inversion recovery, phase-sensitive inversion recovery, and magnetisation-prepared rapid acquisition with gradient echo sequences are required to visualise these lesions. The lesions detected by these techniques are primarily of the leukocortical type; subpial lesions are rarely detected. Care is needed to distinguish potential cortical lesions from neuroimaging artefacts.

Juxtacortical MRI lesion

A T2-hyperintense cerebral white matter lesion abutting the cortex, and not separated from it by white matter.

Periventricular MRI lesion

A T2-hyperintense cerebral white matter lesion abutting the lateral ventricles without white matter in between, including lesions in the corpus callosum but excluding lesions in deep grey matter structures.

Infratentorial MRI lesion

A T2-hyperintense lesion in the brainstem (typically near the surface), cerebellar peduncles, or cerebellum.

Spinal cord MRI lesion

A hyperintense lesion in the cervical, thoracic, or lumbar spinal cord seen on T2 plus short tau inversion recovery, proton-density images, or other appropriate sequences, or in two planes on T2 images.

MRI

Dissemination in space (DIS) can be demonstrated by one or more T2-hyperintense lesions that are characteristic of multiple sclerosis in two or more of four areas of the CNS: periventricular, cortical or juxtacortical, and infratentorial brain regions, and the spinal cord.

Dissemination in time (DIT) can be demonstrated by the simultaneous presence of gadolinium-enhancing and non-enhancing lesions at any time or by a new T2-hyperintense or gadolinium-enhancing lesion on follow-up MRI, with reference to a baseline scan, irrespective of the timing of the baseline MRI.

The 2017 McDonald criteria for diagnosis of multiple sclerosis in patients with an attack at onset

• If the 2017 McDonald Criteria are fulfilled and there is no better explanation for the clinical presentation, the diagnosis is multiple sclerosis.
• If multiple sclerosis is suspected by virtue of a clinically isolated syndrome but the 2017 McDonald Criteria are not completely met, the diagnosis is possible multiple sclerosis.
• If another diagnosis arises during the evaluation that better explains the clinical presentation, the diagnosis is not multiple sclerosis.
• Unless MRI is not possible, brain MRI should be obtained in all patients in whom the diagnosis of multiple sclerosis is being considered. In addition, spinal cord MRI or CSF examination should be considered in patients with insufficient clinical and MRI evidence supporting multiple sclerosis, with a presentation other than a typical clinically isolated syndrome, or with atypical features. If imaging or other tests (eg, CSF) are undertaken and are negative, caution needs to be taken before making a diagnosis of multiple sclerosis, and alternative diagnoses should be considered.
• Clinical diagnosis based on objective clinical findings for two attacks is most secure. Reasonable historical evidence for one past attack, in the absence of documented objective neurological findings, can include historical events with symptoms and evolution characteristic for a previous inflammatory demyelinating attack; at least one attack, however, must be supported by objective findings. In the absence of residual objective evidence, caution is needed.
• The presence of CSF-specific oligoclonal bands does not demonstrate dissemination in time per se but can substitute for the requirement for demonstration of this measure.