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 disease,
osteogenesis imperfecta, trauma, radiation
myelopathy,
vitamin B12 deficiency (
subacute combined degeneration),
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 Lhermitte'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 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 Typically, it only occurs after having taken the medication for some duration, and then stopped or withdrawn rapidly or after administering reduced dose.
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 sign among
nitrous oxide abusers. This is likely due to nitrous oxide depletion of vitamin B12 leading to a very severe, rapid deficiency in the absence of supplementation. ==Terminology==