Lhermitte's sign

Lhermitte's sign or the Lhermitte sign (/lɛrˈmiːt/), sometimes called the barber chair phenomenon, is an electrical sensation that runs down the back and into the limbs. In many patients, it is elicited by bending the head forward. It can also be evoked when a practitioner pounds on the posterior cervical spine while the neck is flexed; this is caused by involvement of the posterior columns.