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Lhermitte's sign or the Lhermitte sign (//), 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.
Lhermitte's sign is named for French neurologist Jean Lhermitte.
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 transverse myelitis, 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. Lhermitte's Sign may also appear during or following high dose chemotherapy. Irradiation of the cervical spine may also evoke it as an early delayed radiation injury, which occurs within 4 months of radiation therapy.
Delayed onset Lhermittes's sign has been reported following head and/or neck trauma. This occurs ~2 1/2 months following injury, without associated neurological symptoms or pain, and typically resolves within 1 year.
This sign is also sometimes seen as part of a "discontinuation syndrome" associated with certain psychotropic medications, such as serotonin reuptake inhibitors, particularly Paroxetine and Venlafaxine. Typically, it only occurs after having taken the medication for some duration, and then stopped or withdrawn rapidly. Fluoxetine, given its very long half-life, can be given as a single small dose, and often avoid Lhermitte's sign and other withdrawal symptoms.
In the dental field, three studies (Layzer 1978, Gutmann 1979, Blanco 1983) have identified Lhermitte's sign among nitrous oxide abusers. This is due to the fact that N2O depletes B12, leading to severe deficiency in the absence of supplementation.
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 Pierre Marie and Chatelin in 1917. Jean Lhermitte, a French neurologist and neuropsychiatrist, 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.
Given that Lhermitte's sign is named for Lhermitte, it is incorrect to spell the term as "L'hermitte's sign".