# Situation: A 30-year-old woman with relapsing-remitting multiple sclerosis (MS) comes to the neurology clinic. She was diagnosed 2 years ago and now takes interferon beta injections and oral baclofen for leg spasticity. Which diagnostic finding supported her diagnosis of multiple sclerosis (MS)?

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## 문제

Situation: A 30-year-old woman with relapsing-remitting multiple sclerosis (MS) comes to the neurology clinic. She was diagnosed 2 years ago and now takes interferon beta injections and oral baclofen for leg spasticity.

Which diagnostic finding supported her diagnosis of multiple sclerosis (MS)?

## 보기

1. A falling response on repeated nerve stimulation
2. A single wedge-shaped lesion on brain imaging
3. Scattered white matter lesions on brain imaging **✔ 정답**
4. Slowed nerve conduction in both legs on testing

**정답: 3**

## 해설

MS is diagnosed by showing demyelinating plaques in different regions of the central nervous system, seen on MRI as scattered white matter lesions, typically periventricular, juxtacortical, infratentorial, and in the spinal cord. Slowed peripheral nerve conduction points to a peripheral neuropathy such as Guillain-Barré syndrome, which MS does not involve. A decremental response to repeated nerve stimulation is typical of myasthenia gravis, and a single wedge-shaped lesion suggests an infarct.

## 심화 해설

Core diagnostic concept Multiple sclerosis is a central nervous system demyelinating disease, not a peripheral nerve disorder. The hallmark finding on MRI is multiple demyelinating plaques scattered in different regions of the CNS white matter, which supports the requirement for dissemination in space [1][3].

Why scattered white matter lesions are diagnostic MS lesions appear as T2-hyperintense foci in characteristic locations: periventricular, juxtacortical, infratentorial, and spinal cord [1][4]. The 2017 and 2024 McDonald criteria require evidence of lesions in at least two of these four CNS regions to establish dissemination in space [1][2]. A single lesion is insufficient unless accompanied by other clinical or paraclinical evidence, which is why a single wedge-shaped lesion suggests an ischemic infarct rather than MS [3].

Differential diagnosis of the distractors

| Finding | Mechanism | Typical condition |
| --- | --- | --- |
| Falling response on repeated nerve stimulation | Postsynaptic acetylcholine receptor fatigue at neuromuscular junction | Myasthenia gravis |
| Single wedge-shaped lesion | Vascular territory occlusion causing localized ischemia | Cerebral infarction |
| Slowed nerve conduction in both legs | Peripheral nerve demyelination or axonal loss | Guillain-Barré syndrome, peripheral neuropathy |

Why peripheral findings exclude MS MS affects only central myelin produced by oligodendrocytes. Peripheral nerve conduction studies evaluate Schwann cell–myelinated axons, which are not involved in MS. Therefore, slowed nerve conduction in the legs points to a peripheral neuropathy, not MS [3]. This distinction is frequently tested because both MS and Guillain-Barré syndrome are demyelinating conditions, but they affect completely different parts of the nervous system.

Clinical correlation with the patient This patient has relapsing-remitting MS with leg spasticity managed by baclofen, a GABA-B agonist that reduces spasticity by acting on the spinal cord. Interferon beta is an immunomodulatory therapy that reduces relapse frequency. The diagnosis was established two years ago, meaning the initial MRI already demonstrated dissemination in space and time through multiple lesions in distinct CNS regions [1][2]. The 2024 McDonald criteria emphasize that MRI remains the cornerstone imaging modality for detecting these demyelinating lesions [3].References (research sources)

- [1]Diagnosis of multiple sclerosis: 2017 revisions of the McDonald criteria.Research articleThompson AJ, Banwell BL, Barkhof F, Carroll WM, Coetzee T, Comi G (2018) · DOI: 10.1016/S1474-4422(17)30470-2

- [2]Application of the 2024 McDonald Criteria: Earlier Diagnosis and Avoiding Misdiagnosis of Multiple Sclerosis in a Global Setting.Research articleSolomon AJ, Brownlee WJ, Viswanathan S, Fadda G, Fiol J, Galleguillos Goiry LM, Griffin T, Sahraian MA, Saylor DR, Rovira À, Flanagan EP, Ramanathan S, as the International Advisory Committee on Clinical Trials in Multiple Sclerosis. (2026) · DOI: 10.1212/wnl.0000000000218425

- [3]ACR Appropriateness Criteria® Demyelinating Diseases.Research articleExpert Panel on Neurologic Imaging, Kalnins A, Lewis LM, Soderlund KA, Austin MJ, Chu S, Hawley DB, Kontzialis M, Levy M, McMenamy J, Ritter JB, Thaker AA, Shih RY. (2026) · DOI: 10.1016/j.jacr.2026.02.003

- [4]Spinal cord imaging in multiple sclerosis: from diagnosis to disease progression.Research articleKoren TJ, Dugal J, Wang D, Beadnall H, Wang CT, Barnett Y, Calamante F, Montalban X, Oh J, Barnett MH. (2026) · DOI: 10.1007/s00415-026-14122-3

## 임상 시나리오

MS Diagnosis: MRI FindingsCentral vs. peripheral demyelination
Multiple sclerosis is a central nervous system demyelinating disease. The hallmark MRI finding is scattered white matter lesions in characteristic locations: periventricular, juxtacortical, infratentorial, and spinal cord.

The McDonald criteria require evidence of lesions in at least two of these four CNS regions to establish dissemination in space. A single lesion is insufficient for diagnosis.

CautionSlowed nerve conduction and decremental responses on repetitive stimulation indicate peripheral nerve or neuromuscular junction pathology, not MS. MS affects only oligodendrocyte-myelinated CNS axons.

## 핵심 개념

- **Dissemination in space** — McDonald criteria requirement for MS diagnosis: lesions in at least two of four characteristic CNS regions (periventricular, juxtacortical, infratentorial, spinal cord).
- **Demyelinating plaque** — Focal area of myelin loss in the CNS, appearing as T2-hyperintense white matter lesions on MRI.
- **Oligodendrocyte** — CNS cell that produces myelin; its destruction underlies MS pathology, distinguishing it from peripheral nerve disorders.
- **McDonald criteria** — Diagnostic guidelines for MS that combine clinical attacks with MRI evidence of lesion dissemination in space and time.
- **Periventricular** — One of the characteristic CNS locations for MS plaques, adjacent to the ventricles.

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