MRI in Multiple Sclerosis — Diagnosis & Monitoring

MRI in Multiple Sclerosis

MRI is central to diagnosing MS and to tracking it over a lifetime — it shows the disease’s hallmark of lesions scattered across the CNS and accumulating over time.

The two core concepts

Diagnosis (McDonald criteria) rests on demonstrating:

Dissemination in space (DIS): lesions in ≥2 of the four typical CNS locations.
Dissemination in time (DIT): new lesions over time, or the simultaneous presence of enhancing and non-enhancing lesions on one scan.

Gadolinium enhancement marks an active lesion (breakdown of the blood–brain barrier), lasting weeks — so an enhancing plus a non-enhancing lesion can prove “time” on a single scan.

Typical locations & appearances

Periventricular: ovoid lesions perpendicular to the ventricles (“Dawson’s fingers”).
Juxtacortical/cortical, infratentorial (brainstem/cerebellum), and spinal cord — the four McDonald sites.
Lesions are T2/FLAIR-hyperintense; some become T1 “black holes” reflecting axonal loss.

Monitoring

Standardised, comparable MRI is used to detect new/enlarging lesions, guiding treatment decisions and detecting subclinical activity. Consistent protocol and slice positioning matter enormously for reliable comparison — the same reproducibility discipline that applies across MRI. Emerging markers include the central-vein sign and paramagnetic-rim lesions.

Reference: Thompson AJ et al. Diagnosis of multiple sclerosis: 2017 revisions of the McDonald criteria. Lancet Neurol 2018;17:162–73.

Educational summary for clinicians; diagnosis is clinical-radiological. Not medical advice.