Well we all know about the Lhermitte’s sign... The famous Barber's Chair sign!
For the people who are reading for the first time... Lhermitte's sign is a sensation of tingling or electric shocks running down the back and legs on flexion of the neck.
Some other actions giving rise to similar sensations are: Neck rotation, arm abduction, coughing ,Yawning
It is common in multiple sclerosis, and other demyelinating diseases but can occur with other conditions involving the cervical spinal cord.
But...Some variants to Lhermitte’s sign have also been described.
1) Delayed typical Lhermitte phenomenon can follow contusion of the spinal cord from neck trauma.
2) Reverse Lhermitte phenomenon
Paresthesias induced by neck extension have been described in extrinsic compression of the cervical spinal cord.
3) Inverse Lhermitte's sign:
Upward moving paresthesias with neck flexion have been described in myelopathy from nitrous oxide inhalation.
I hope this was informative!