# Multiple Sclerosis > Multiple sclerosis for NEET-PG Medicine: McDonald criteria dissemination in time and space, CSF oligoclonal bands, relapse and DMT choices and the NMO contrast. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/multiple-sclerosis - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Multiple Sclerosis", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/multiple-sclerosis ## Direct answer An immune-mediated demyelinating disease of the central nervous system, multiple sclerosis is diagnosed by demonstrating lesions disseminated in time and space — the McDonald criteria — clinically and on MRI, supported when needed by cerebrospinal fluid oligoclonal bands. Around 85 per cent begin as relapsing-remitting disease with attacks such as optic neuritis, transverse myelitis or brainstem syndromes; acute relapses receive high-dose methylprednisolone, and disease-modifying therapy — injectables, oral agents such as fingolimod and dimethyl fumarate, or monoclonal antibodies such as natalizumab — is chosen by activity and risk, distinguishing MS throughout from neuromyelitis optica spectrum disorder, its AQP4-antibody-driven look-alike. ## What you must remember - Dissemination in space (DIS): at least two lesions in typical locations — periventricular, cortical/juxtacortical, infratentorial, spinal cord; dissemination in time (DIT): a new lesion on follow-up MRI, simultaneous enhancing and non-enhancing lesions, or oligoclonal bands. - MRI signature: ovoid periventricular lesions perpendicular to the ventricular wall ("Dawson fingers"), infratentorial and spinal cord lesions; spinal lesions typically span fewer than two vertebral segments. - CSF: oligoclonal bands unique to CSF (absent in matched serum) with normal cell count and mildly raised protein — supportive, not mandatory, with typical MRI. - Classic syndromes: optic neuritis (painful monocular visual loss, relative afferent pupillary defect), partial myelitis, internuclear ophthalmoplegia (young person with binocular diplopia — a viva favourite), Lhermitte's sign, Uhthoff's phenomenon (heat-worsened symptoms). - Acute relapse: methylprednisolone 1 g intravenously daily for 3–5 days; plasma exchange for severe steroid-refractory attacks. - DMT ladder: platform injectables (interferon beta, glatiramer acetate); oral agents — fingolimod (first-line monitoring for bradycardia, macular oedema; PML risk), dimethyl fumarate (lymphopenia, flushing), teriflunomide (teratogenic); monoclonal antibodies — natalizumab (high efficacy; progressive multifocal leukoencephalopathy risk governed by JC virus serology) and alemtuzumab (autoimmune secondary events). - Primary progressive MS responds to ocrelizumab alone among tested agents; symptomatic care (spasticity, fatigue, bladder) runs parallel. - NMOSD contrast: AQP4-IgG seropositivity, longitudinally extensive transverse myelitis spanning three or more segments, severe bilateral optic neuritis, intractable hiccups or area postrema syndrome, MRI lesions atypical for MS, CSF pleocytosis above about 50 cells with fewer oligoclonal bands — treated with rituximab or azathioprine, not MS DMTs, and misdiagnosis worsens outcomes. ## Applying McDonald to one admission A 26-year-old woman presents with a week of painful blurred vision in the right eye; two years earlier she had numbness from the waist down that resolved over a month and was called a "vitamin problem". Step one, recognise clinically isolated syndrome with a past attack: two separate anatomical locations already suggest dissemination in space. Step two, MRI brain and cervical spine: the optic nerve lesion aside, periventricular ovoid lesions plus a single-segment cervical cord lesion satisfy DIS; the presence of both enhancing and non-enhancing lesions in the same scan satisfies DIT without waiting for a second MRI. Step three, decide on CSF: with a typical MRI, oligoclonal bands are optional; where imaging is atypical, they are the tie-breaker, and if the myelopathy lesion had instead spanned six cord segments, the pathway forks — test AQP4-IgG, because longitudinally extensive myelitis plus severe optic neuritis defines NMOSD, whose treatment is rituximab or azathioprine with steroid sparing, and MS immunotherapies can actively harm it. Step four, treat the relapse: methylprednisolone 1 g daily for three to five days. Step five, choose maintenance by risk: a young woman planning pregnancy might start with an injectable or consider ocrelizumab; highly active disease pushes toward natalizumab, gated by JC virus serology because of progressive multifocal leukoencephalopathy; monitoring — blood counts, liver function, MRI surveillance at defined intervals — is part of the prescription. ## Where students slip The recurring mistakes: quoting "dissemination in time and space" without being able to operationalise either on an MRI report, which is exactly what the viva demands; treating internuclear ophthalmoplegia in a young adult as a microvascular palsy of the older patient; and, most consequential, labelling longitudinally extensive transverse myelitis as aggressive MS — the three-vertebral-segment threshold and the AQP4-IgG test separate NMOSD, and the treatments are not interchangeable. A subtler error is forgetting that primary progressive MS has essentially one evidence-backed DMT (ocrelizumab), so "start interferon" is the planted wrong answer in that stem. ## Frequently asked questions ### What constitutes dissemination in time under the McDonald criteria? A new T2 or gadolinium-enhancing lesion on follow-up MRI, simultaneous enhancing and non-enhancing lesions on a single scan, or CSF-specific oligoclonal bands. ### Which CSF finding supports multiple sclerosis? Oligoclonal immunoglobulin G bands present in CSF but absent in matched serum, with otherwise near-normal cell count and protein. ### What characterises an MS spinal cord lesion on MRI? A lesion shorter than two vertebral segments, typically lateral and peripheral — in contrast to the longitudinally extensive lesions of three or more segments in NMOSD. ### How is an acute MS relapse treated? High-dose methylprednisolone, typically 1 g intravenously daily for three to five days, with plasma exchange considered for severe steroid-refractory attacks. ### Which features distinguish NMOSD from multiple sclerosis? AQP4-IgG positivity, longitudinally extensive transverse myelitis, severe or bilateral optic neuritis, area postrema syndrome (intractable hiccups, vomiting), atypical brain MRI and fewer oligoclonal bands — treated with rituximab or azathioprine rather than MS DMTs.