Lhermitte’s Sign is a neurological symptom characterized by a sudden, transient electrical sensation that travels down the spine and into the limbs. This phenomenon is often startling and uncomfortable, raising concerns about the potential severity of the underlying cause. While the sensation itself is not physically damaging, its occurrence warrants a thorough medical investigation. It serves as an indicator of irritation or damage within the central nervous system, signaling that a deeper, potentially serious condition requires professional attention.
Understanding the Sensation
Lhermitte’s Sign is described as a sharp, electric-shock sensation or a strong buzzing feeling that originates in the neck. This sensation abruptly runs down the spine, frequently radiating outward into the arms, legs, and sometimes the torso. It is a paroxysmal symptom, meaning it is short-lived, typically lasting only a few seconds per episode.
The sensation is almost always triggered by specific movements, primarily the forward flexion of the neck, which is why it is sometimes referred to as the “barber chair phenomenon.” Bending the head forward stretches the spinal cord within the cervical canal. This movement pulls on the dorsal columns of the upper spinal cord, where the sensory nerves responsible for touch and proprioception are located.
The underlying mechanism involves damage to the protective coating around the nerve fibers, known as the myelin sheath, in the cervical spine. When the myelin is damaged, the nerve becomes hyperexcitable, causing it to misfire an electrical signal when stretched. The brain interprets this abnormal, rapid firing as a painful electric shock traveling through the body.
Underlying Neurological Conditions
The presence of Lhermitte’s Sign is suggestive of irritation or compression affecting the cervical spinal cord. Multiple Sclerosis (MS) is the most recognized association, as demyelination of the spinal cord frequently occurs in this autoimmune disease. Studies indicate that up to one-third of individuals diagnosed with MS experience this sensation at least once in their lifetime.
Beyond MS, other demyelinating disorders, such as Neuromyelitis Optica Spectrum Disorder (NMOSD), can also cause this reaction. The sign can also result from a structural issue causing physical compression of the spinal cord, including cervical spondylosis or a herniated disk.
Lhermitte’s Sign can also arise from acquired causes:
- Radiation myelopathy, which is nerve damage after therapeutic radiation to the neck or spine.
- Severe deficiency of Vitamin B12, which damages the spinal cord.
- Traumatic injuries to the neck or spinal cord.
Assessing the Symptom’s Clinical Significance
The primary concern for most people experiencing this symptom is whether Lhermitte’s Sign itself poses an immediate physical threat. The sensation is not inherently dangerous; it is a temporary neurological signal. The shock-like feeling is uncomfortable and startling but does not cause physical harm to the spinal cord or brain during the episode.
The significance of the symptom lies entirely in the underlying medical condition it reflects. When Lhermitte’s Sign occurs in isolation, such as following neck trauma or a transient infection, it may resolve completely within months to a year. However, if it appears alongside other neurological symptoms like muscle weakness, vision changes, or problems with balance, it is far more concerning.
A medical evaluation is necessary to distinguish between a temporary cause and a chronic, progressive disease. Lhermitte’s Sign can be an early indicator of a demyelinating disease, prompting early diagnosis and treatment. The symptom acts as a physiological alarm, demanding attention to the root cause.
Diagnostic Procedures and Treatment Approaches
Evaluation of Lhermitte’s Sign begins with a detailed neurological examination and patient history. The physician will perform the physical maneuver that triggers the sensation, such as asking the patient to flex their head forward, to confirm the sign. The diagnostic workup focuses on identifying the specific pathology affecting the cervical spinal cord.
Magnetic Resonance Imaging (MRI) of the brain and cervical spine is the preferred imaging modality. This test can reveal demyelinating lesions characteristic of MS, structural compression from spondylosis or tumors, or inflammation. Blood tests are also routinely ordered to rule out treatable metabolic causes, such as checking Vitamin B12 levels.
Treatment is centered on managing the underlying condition, as the symptom frequently resolves once the primary issue is addressed. If a Vitamin B12 deficiency is the cause, supplementation can resolve the symptom entirely. For conditions like MS, treatment involves disease-modifying therapies to reduce inflammation and prevent further nerve damage.
In cases where the sensation is particularly bothersome, certain medications, such as anticonvulsants like gabapentin, may be used temporarily to reduce the nerve’s hyperexcitability. Long-term management always targets the root cause of the spinal cord irritation.