A 28-year-old woman from Delhi presents with acute onset blurred vision in the left eye and pain on eye movement for 3 days. Fundoscopy reveals a swollen optic disc. MRI brain with contrast shows T2 hyperintense lesion in the left optic nerve with perilesional edema and central enhancement. CSF analysis shows oligoclonal bands. What is the most likely diagnosis?

Explanation

## Clinical Presentation & MRI Findings **Key Point:** Optic neuritis with perilesional edema and central enhancement on MRI, combined with oligoclonal bands in CSF, is highly suggestive of demyelinating disease. **High-Yield:** In a young woman presenting with monocular vision loss and pain on eye movement (typical of optic neuritis), the presence of oligoclonal bands indicates an inflammatory demyelinating process. The MRI finding of T2 hyperintensity with perilesional edema in the optic nerve is characteristic of demyelination. ## Differential Diagnosis | Feature | MS with Optic Neuritis | ADEM | NMOSD | Leber Hereditary | |---------|------------------------|------|-------|------------------| | **Age of onset** | 20–40 years (F > M) | Children/young adults | Any age | Young males | | **Optic nerve involvement** | Unilateral, common | Bilateral possible | Bilateral, severe | Bilateral | | **CSF oligoclonal bands** | Positive (90%) | Negative/rare | Negative | Negative | | **Brain MRI lesions** | Multiple, periventricular | Multifocal, large | Longitudinal myelitis | Normal | | **Spinal cord involvement** | Short segment | Possible | Longitudinal (>3 segments) | None | | **AQP4 antibodies** | Negative | Negative | Positive (60–90%) | Negative | **Clinical Pearl:** Oligoclonal bands in CSF are a hallmark of MS and distinguish it from ADEM (which typically has negative bands) and NMOSD (which is seronegative for OCBs). The unilateral presentation of optic neuritis with perilesional edema is classic for MS rather than the bilateral presentation seen in NMOSD. **Mnemonic: NMOSD Red Flags** — **LONG** = Longitudinal myelitis (>3 segments), Optic neuritis (often bilateral), Negative OCBs, Glial fibrillary acidic protein (GFAP) or AQP4 antibodies. This case lacks longitudinal myelitis and has positive OCBs, making MS the answer. ## Why MS (with optic neuritis) is the answer 1. **Oligoclonal bands** are present in 90% of MS patients but are rare or absent in ADEM and NMOSD. 2. **Unilateral optic neuritis** is the most common demyelinating event in MS; bilateral involvement is more suggestive of NMOSD. 3. **Perilesional edema with central enhancement** is typical of MS demyelinating lesions. 4. **Age and sex** (28-year-old woman) fit the classic MS demographic. ## MRI Features of MS Demyelination - **T2/FLAIR hyperintensity** in white matter, optic nerve, or spinal cord - **Perilesional edema** indicating active inflammation - **Central enhancement** on post-gadolinium T1 (blood–brain barrier breakdown) - **Dawson's fingers** (periventricular lesions oriented perpendicular to ventricles) - **Ovoid lesions** in the corpus callosum [cite:Harrison 21e Ch 380]