Lhermitte's sign

Lhermitte's Sign, sometimes called the Barber Chair phenomenon, is an electrical sensation that runs down the back and into the limbs, and is produced by bending the neck forward. The sign suggests a lesion of the dorsal columns of the cervical cord or of the caudal medulla. Although often considered a classic finding in multiple sclerosis, it can be caused by a number of conditions, including Behçet's disease, trauma, radiation myelopathy, vitamin B12 deficiency (subacute combined degeneration), and compression of the spinal cord in the neck from any cause such as cervical spondylosis, disc herniation, tumor, and Arnold-Chiari malformation.

Strictly speaking, the Barber Chair phenomenon is a symptom rather than a sign as it describes a subjective sensation rather than an objective finding. To add more confusion, it is not attributed to its discoverer. It was first described by Marie and Chatelin in 1917. Jean Lhermitte did not publish his first report until 1920. However, in 1924 he did publish the seminal article on the subject which resulted in it becoming well known.

Most modern editors prefer the non-possessive form for medical eponyms: Lhermitte sign.