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. Examination reveals relative afferent pupillary defect and reduced colour vision. MRI brain with contrast shows a T2-hyperintense lesion in the left optic nerve with central gadolinium enhancement. CSF analysis shows oligoclonal bands. What is the most likely diagnosis and what is the significance of the imaging finding?

Explanation

## Clinical Presentation & Diagnosis This patient presents with a **clinically isolated syndrome (CIS)** — specifically optic neuritis — which is a demyelinating event. The presence of oligoclonal bands in CSF and the imaging findings are consistent with **multiple sclerosis (MS)**. ## MRI Findings in Demyelinating Optic Neuritis **Key Point:** Gadolinium enhancement in acute demyelinating optic neuritis indicates active inflammation with **blood-brain barrier (BBB) disruption**. This is a hallmark of acute demyelinating disease. ### Enhancement Patterns | Feature | Acute Demyelination | Chronic/Resolved | |---------|-------------------|------------------| | **Gadolinium enhancement** | Present (BBB disruption) | Absent | | **T2 signal** | Hyperintense | May persist | | **Clinical correlation** | Active inflammation | Residual damage | | **Prognosis** | Reversible with treatment | Fixed deficit | **High-Yield:** Gadolinium enhancement = **active inflammation**, not severity. It indicates the lesion is recent (days to weeks old) and the BBB is compromised. ## Why This Is MS, Not Other Demyelinating Diseases 1. **Oligoclonal bands in CSF** — highly specific for MS (present in ~95% of MS patients) 2. **Optic neuritis as CIS** — 50% of patients with optic neuritis will develop MS within 15 years 3. **Central nervous system involvement** — MS typically affects brain and spinal cord **Clinical Pearl:** The **Optic Neuritis Treatment Trial (ONTT)** showed that patients with optic neuritis who have abnormal brain MRI (≥3 T2 lesions) have a 50% risk of developing clinically definite MS within 15 years, rising to ~80% over 20 years. ## Differential Considerations **ADEM:** Typically presents with multifocal involvement, often follows viral infection, and usually occurs in children/young adults with rapid progression. CSF oligoclonal bands are less common. **NMOSD:** Characterized by **longitudinally extensive transverse myelitis (LETM)** and optic neuritis, but optic nerve enhancement is NOT pathognomonic — it occurs in MS as well. NMOSD is distinguished by aquaporin-4 (AQP4) antibodies and specific spinal cord involvement patterns. **Leber Hereditary Optic Neuropathy:** A mitochondrial disorder causing painless, progressive vision loss without enhancement on MRI. No inflammatory features. [cite:Harrison 21e Ch 380]