Lhermitte's sign

Lhermitte's phenomenon or the Lhermitte phenomenon (/lɛərˈmiːt/), 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 is subjective and therefore a symptom.

Lhermitte's phenomenon is named for French neurologist Jean Lhermitte.

The sign 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. 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.

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