Clinically isolated syndrome is defined as:

• A. Multiple episodes of neuro symptoms separated in time.
• B. A single episode of neuro symptoms that may indicate MS.
• C. Radiologic findings without clinical symptoms.
• D. Progressive disability from onset.

Answer: (B)

Clinically isolated syndrome is a single clinical episode of neurological symptoms lasting at least 24 hours that is typical of a demyelinating attack and may herald multiple sclerosis. It captures the idea of one acute event that could progress to MS, rather than multiple separate attacks, radiologic-only findings, or a disease that is progressive from the start. The other descriptions don’t fit: multiple episodes imply dissemination in time, radiologic findings without symptoms describe a radiologic isolated syndrome, and progressive onset describes a different MS course (progressive MS) rather than a first isolated event.