Dissemination in time in the McDonald criteria is demonstrated by lesions appearing at multiple times.

• A. Lesions appear in multiple areas but at one time.
• B. Lesions appear at multiple times.
• C. Only one plaque is present.
• D. It is not part of the McDonald criteria.

Answer: (B)

Dissemination in time means there has been disease activity at more than one point in time. In MS, this is shown on MRI when lesions differ in age within the same study: for example, a gadolinium-enhancing lesion indicating a new, active lesion alongside older non-enhancing T2 lesions, or a new lesion appearing on a follow-up scan. This demonstrates that lesions didn’t all form at once, but at multiple times. That’s why this statement is the best answer. If lesions are in several areas at one time, that shows dissemination in space, not time. Having only a single plaque doesn’t show time-based spread, and the McDonald criteria do include dissemination in time.