Lhermitte’s sign is a neurological symptom characterized by a sudden, transient electrical sensation that travels down the body. This sensation is reliably triggered by the flexion of the neck, which involves bending the head forward toward the chest. It is a physical manifestation indicating irritation or damage to the sensory pathways within the central nervous system. The episodes are short-lived, coming in sudden bursts known as paroxysmal pain.
Describing the Lhermitte’s Sensation
Patients frequently describe the sensation as feeling like a sharp, electric shock or a powerful jolt of electricity. This feeling starts in the neck and rapidly shoots downward along the length of the spine. It can feel like touching a live wire, earning it the alternative name of “barber chair phenomenon.”
The electricity-like feeling often radiates outward from the trunk. It may extend into the arms, legs, and occasionally even into the fingers and toes. The sensation is extremely brief, typically lasting only a few seconds before disappearing as soon as the neck returns to a neutral position.
Clinicians can deliberately elicit the sign by asking a patient to touch their chin to their chest, a movement that stretches the spinal cord. The sensation starts and stops immediately with this triggering movement. Other rapid movements or actions that stretch the neck, such as coughing or sneezing, can also sometimes provoke the symptom.
The Physiological Basis of the Sign
Lhermitte’s sign arises from a physical irritation or hyperexcitability of the sensory tracts in the cervical spinal cord, specifically the dorsal columns. These columns are bundles of nerve fibers responsible for transmitting information about touch, vibration, and position sense to the brain. When the neck is flexed, the spinal cord is stretched, increasing the mechanical tension on these nerve fibers.
The underlying mechanism often involves the demyelination of these nerve fibers, which is the loss of the protective fatty sheath called myelin. Myelin normally acts as an insulator, ensuring that electrical signals travel quickly and cleanly along the axon. When the sheath is damaged, the exposed axon becomes hypersensitive to mechanical stimulation, a phenomenon known as mechanosensitivity.
The stretching of the cord during neck flexion acts as a mechanical stimulus on the exposed, damaged axons in the dorsal columns. This stimulation causes the nerves to misfire, generating an abnormal, intense electrical impulse that the brain interprets as a sudden shock or a buzzing sensation.
Primary Conditions Associated with the Sign
Lhermitte’s sign points to a problem in the cervical spinal cord, but it is not specific to a single disease and requires clinical investigation to determine the root cause. It is most commonly associated with Multiple Sclerosis (MS), an autoimmune disorder that attacks the myelin sheath in the central nervous system. Studies suggest that up to one-third of people with MS will experience this symptom.
The sign can also be caused by structural issues that physically compress or deform the spinal cord in the neck region. Conditions such as cervical spondylosis, which involves age-related wear and tear of the spinal discs and vertebrae, or a herniated disc can put pressure on the sensory pathways. Trauma to the neck, such as whiplash, can similarly cause temporary irritation leading to the symptom.
Other causes of demyelination or irritation include:
- Severe Vitamin B12 deficiency. Since Vitamin B12 is necessary for myelin maintenance, a long-term deficiency can lead to subacute combined degeneration.
- Radiation myelopathy, which is a delayed side effect following radiation therapy to the head or neck area.
- Inflammatory conditions that affect the spinal cord, such as transverse myelitis.
Approaches to Symptom Management
Management focuses on reducing the frequency of episodes, as the sensation only lasts while the neck is in a flexed position. A simple, non-pharmacological approach is to increase awareness of the triggering movements and consciously avoid them. Patients can be advised to move their neck more slowly or limit the degree of forward flexion during daily activities.
Wearing a soft cervical collar for brief periods can help restrict neck movement and prevent the triggering stretch of the spinal cord. Physical or occupational therapy may be beneficial by helping a person learn better posture and neck stabilization techniques. These methods aim to reduce the mechanical stress placed on the irritated nerve pathways.
For individuals who experience Lhermitte’s sign frequently and find it disruptive, pharmacological treatments are available to reduce nerve hyperexcitability. Low-dose anticonvulsant medications, such as gabapentin or carbamazepine, are often prescribed to stabilize the damaged nerve membranes and suppress the abnormal firing of electrical impulses. If the symptom is part of an acute inflammatory flare-up of a condition like MS, a healthcare provider may recommend a short course of corticosteroids.