A 30 year old woman from Denmark presents with a several year history of intermittent sensory changes in her arms, legs, and face. From time to time, she will get in numbness or tingling but they usually self-resolve in time. She's also had episodes of double vision, vision loss, and problems with walking. On exam, when you flex her neck, she gets electric shock-like sensations that run down her back. T1-weighted MRI monthly scans are shown above.
Challenge: What's the diagnosis?
1. What's the sign elicited on exam?
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