Lhermitte’s sign describes a brief, transient sensation that feels like an electric shock traveling down the spine and into the limbs. This symptom is typically triggered by movements of the neck, particularly bending the head forward toward the chest, which is why it is sometimes called the “barber chair phenomenon.” Although the sensation is not inherently dangerous, it warrants immediate medical evaluation because it is a marker for an underlying condition affecting the spinal cord, some of which require urgent attention.
Understanding Lhermitte’s Sign
Lhermitte’s sign is a neurological symptom characterized by a sudden, intense, shock-like sensation that begins in the neck and rapidly travels downward. The sensation often radiates down the spine and may branch out into the arms, legs, or toes, feeling like a jolt of electricity. It is classified as a paroxysmal symptom, meaning it occurs in short, sudden bursts that usually last only a few seconds.
The physiological mechanism behind this symptom involves irritation or hyperexcitability of the sensory pathways within the cervical spinal cord, specifically the dorsal columns. These columns carry information about touch, vibration, and position from the body to the brain. When the neck is flexed, the spinal cord is stretched, causing a mechanical stimulation of damaged nerve fibers.
The damage often involves demyelination, which is the loss of the protective myelin sheath surrounding the nerve fibers. Myelin helps electrical signals travel smoothly; without it, the nerve fibers are exposed and become overly sensitive to stretching or pressure, causing them to misfire and create the shock-like sensation. Lhermitte’s sign is a symptom of this nerve pathway dysfunction and not a standalone disease.
The Spectrum of Underlying Causes
The potential danger associated with Lhermitte’s sign depends entirely on the specific underlying condition causing the spinal cord irritation. Causes fall across a wide spectrum, from chronic conditions to temporary, easily treatable issues.
Multiple Sclerosis (MS) is the most common chronic cause, often being one of the initial symptoms in younger populations. In MS, the immune system attacks the myelin sheath in the central nervous system, leading to inflammatory lesions in the cervical spinal cord that trigger the sign. The sign confirms nerve damage is present.
More urgently, Lhermitte’s sign can be a sign of mechanical compression of the spinal cord. This compression can be caused by cervical spondylosis (age-related arthritis), a spinal cord tumor, a herniated disc, or a traumatic spinal cord injury. These compressive causes demand swift medical intervention to prevent progressive and permanent neurological damage.
Less severe causes include nutritional deficiencies and certain medical treatments. A Vitamin B12 deficiency can lead to subacute combined degeneration, which demyelinates the dorsal columns and produces the sign. Individuals who have undergone radiation therapy for cancer in the head or neck area may also develop radiation myelopathy, which can cause Lhermitte’s sign as a delayed side effect.
Medical Evaluation and Next Steps
If you experience Lhermitte’s sign without a known cause, consulting a healthcare provider, ideally a neurologist, is necessary. The diagnostic process begins with a thorough medical history and a physical examination, where the doctor may intentionally provoke the sign by gently testing neck movements.
Imaging is a crucial next step, with Magnetic Resonance Imaging (MRI) of the cervical spine being the preferred method. The MRI allows doctors to identify lesions suggestive of MS, signs of spinal cord compression from tumors or arthritis, or evidence of injury. Blood tests are also routinely ordered to check for specific issues, most commonly screening for Vitamin B12 deficiency.
Management is directed at the underlying cause. For example, if MS is the cause, the sign may resolve as part of a flare-up treated with steroids. In the case of B12 deficiency, the sign typically disappears once appropriate vitamin supplementation is started. For mechanical compression, treatment may range from physical therapy and cervical collars to surgical intervention to relieve pressure on the spinal cord.