Lhermitte's phenomenon, sometimes called the barber chair phenomenon, is an electrical sensation that runs down the back and into the limbs. The sensation can feel like it goes up or down the spine. It is generally considered uncomfortable.
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. It is sometimes called Lhermitte's sign, though this is technically incorrect as a sign is something that can be observed on examination whereas a symptom is the subjective experience. Lhermitte's phenomenon (named for French neurologist Jean Lhermitte) is subjective and therefore a symptom.
The phenomenon suggests a lesion or compression of the upper cervical spinal cord or lower brainstem — usually dorsal columns of the cervical cord or 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.
In the palliative care setting, it is most likely to be associated with chemotherapy toxicity (platinum compounds) or irradiation of the cervical spinal cord..
Delayed onset Lhermitte's has been reported following head and/or neck trauma — this occurs about 2.5 months following injury, without associated neurological symptoms or pain, and typically resolves within 1 year.
This phenomenon is also sometimes seen as part of a "discontinuation syndrome" associated with certain psychotropic medications, such as selective serotonin reuptake inhibitors and serotonin norepinephrine reuptake inhibitors, particularly paroxetine and venlafaxine. Typically, it only occurs after having taken the medication for some duration, and then stopped or withdrawn rapidly or after administering a reduced dose. Fluoxetine, given its very long half-life, can be given as a single small dose, and often avoid Lhermitte's and other withdrawal symptoms.