The McDonald criteria 2017 for multiple sclerosis require dissemination in space (DIS) and dissemination in time (DIT). DIT can now be fulfilled by simultaneous presence of symptomatic and asymptomatic contrast-enhancing and non-enhancing lesions. This change allows MS diagnosis after how many clinical attacks?

• A Three attacks separated by at least 3 months
• B Two attacks on separate occasions
• C One attack (clinically isolated syndrome) with simultaneous enhancing and non-enhancing MRI lesions ✓
• D Requires radiological evidence only, without clinical attack

Explanation

The 2017 McDonald criteria allow diagnosis of MS after a single clinical attack (clinically isolated syndrome, CIS) if MRI shows both contrast-enhancing and non-enhancing lesions simultaneously — this fulfils DIT (enhancing lesion is 'new', non-enhancing lesion is 'old') and if DIS is also satisfied. This accelerated the diagnosis from two attacks to one, enabling earlier initiation of disease-modifying therapy. The criteria also allow DIS to be inferred from CSF oligoclonal bands in some scenarios.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.