Lhermitte’s sign is a neurological symptom characterized by a sudden, often startling, sensation that patients typically describe as an electric shock. This brief, intense feeling originates in the neck and moves quickly down the spine, sometimes radiating into the limbs. It is often referred to as the “barber chair phenomenon” because the specific movement that triggers it is similar to the positioning of the head in a barber’s chair. Lhermitte’s sign is an indication of an underlying problem affecting the nervous system, not a disease itself. The sensation is transient, lasting only a few seconds, but it prompts a thorough medical investigation.
Defining the Sensation and Trigger
The experience of Lhermitte’s sign is described as a swift and intense lightning-bolt or electric-shock sensation. It often starts at the top of the neck and travels rapidly down the back and trunk, sometimes spreading outward into the arms, legs, and even the fingers and toes.
The defining feature is its specific mechanical trigger: the forward flexion of the neck. Bending the head forward, bringing the chin toward the chest, typically precipitates the sudden electrical discharge. Other movements, such as coughing, sneezing, or yawning, can also sometimes generate the sensation.
The sensation is paroxysmal, occurring in short, sudden bursts that resolve immediately upon straightening the neck. While uncomfortable, it is generally not considered life-threatening. Fatigue, stress, or being overheated may increase the likelihood or intensity of the episodes.
The Neurological Mechanism
Lhermitte’s sign stems from irritation or damage within the sensory pathways of the cervical spinal cord, specifically affecting the dorsal columns. These columns contain nerve fibers responsible for transmitting sensory information, such as vibration and position sense. The most common cause of this irritation is demyelination, the destruction of the myelin sheath that insulates nerve fibers.
When the myelin is damaged, the underlying nerve axon becomes hypersensitive and excitable. Flexing the neck causes a slight stretching of the spinal cord, physically pulling on these unprotected nerve fibers. This mechanical irritation causes the damaged nerve to fire an abnormal electrical signal, which the brain interprets as a sudden shock traveling down the body.
Primary Conditions Associated with the Sign
The most common condition associated with Lhermitte’s sign is Multiple Sclerosis (MS), a chronic disease involving demyelination of the central nervous system. Approximately one-third of people diagnosed with MS will experience this symptom at least once. For some individuals, Lhermitte’s sign can be an early or recurring symptom of an MS flare-up.
The sign is not exclusive to MS and can arise from other issues affecting the cervical spinal cord. Structural problems in the neck are a significant category of causes, including cervical spondylotic myelopathy. This occurs when degenerative changes, such as disc herniation or spinal stenosis, lead to spinal cord compression.
Other underlying causes involve damage from external factors or nutritional deficits. These include radiation myelopathy, which is damage occurring after therapeutic radiation for cancer treatment. Furthermore, a severe deficiency in Vitamin B12 can impair the production and maintenance of myelin, causing neurological symptoms that include this electrical sensation.
Symptom Management and Outlook
The primary focus of management is to identify and treat the underlying cause of the spinal cord irritation. For instance, symptoms related to Vitamin B12 deficiency may resolve completely once appropriate supplementation is received. If the sign is related to an MS flare-up, managing the underlying disease with appropriate therapies is the most direct approach.
For symptomatic relief, especially when the sensation is frequent or intense, certain medications can be helpful. Low doses of anticonvulsant medications, such as Gabapentin or Carbamazepine, are often prescribed because they stabilize nerve membranes and reduce the abnormal firing of signals. Patients can also manage the symptom by avoiding the specific neck movements that trigger the electrical sensation.
Lhermitte’s sign is often a transient symptom, meaning it can disappear on its own after the underlying inflammation or acute event resolves. For many, the sign resolves within a few months to a year. While the symptom can be unsettling, its presence signals the need for medical evaluation to address the root neurological issue.