Lhermitte's phenomenon is a transient, sensory symptom which likens an electric shock that radiates down the spine or into the limbs.
The sensation is triggered by neck flexion. The frequency with which they occur varies and the slightest movement of the head or neck may trigger it.
This phenomenon occurs most frequently with multiple sclerosis, but can also be seen with other lesions of the cervical cord, including tumors, disc herniation, post-radiation myelopathy, and following trauma.
References
Kanchandani R, Howe JG. "Lhermitte's sign in multiple sclerosis: a clinical survey and review of the literature." Journal of Neurol Neurosurg Psychiatry. 1982;45(4):308-12.
