An active lesion is an area in the brain or spinal cord where inflammation is happening right now — not an old scar, but a sign of current MS disease activity. Doctors identify active lesions during an MRI by injecting a contrast dye called gadolinium into the bloodstream. This dye "lights up" areas of fresh inflammation Show Full Answer
An active lesion is an area in the brain or spinal cord where inflammation is happening right now — not an old scar, but a sign of current MS disease activity. Doctors identify active lesions during an MRI by injecting a contrast dye called gadolinium into the bloodstream. This dye "lights up" areas of fresh inflammation, making them appear as bright spots on the scan.
Here's what that means in practice:
- Healthy brain MRI: No areas light up with the dye, and the brain looks consistent between scans
- MS brain MRI with active lesions: New bright spots appear after the dye is injected, signaling recent inflammation
- Older lesions: These don't light up — they're settled scars from past activity
Active lesions are one of the clearest signs that MS is still active, even if no new symptoms have been noticed. This information helps a neurologist decide whether to start or adjust a disease-modifying therapy (DMT).
September 25
Join
Your Privacy Choices
