What is Lhermitte's sign?

Lhermitte's Sign: Clinical Significance and Management

Lhermitte's sign is characterized by an electric shock-like sensation that radiates down the spine when the neck is flexed, and may also be felt in the upper and lower limbs. This neurological phenomenon indicates pathology affecting the cervical spinal cord.

Definition and Clinical Presentation

• Lhermitte's sign was first described by Pierre Marie and Chatelin in 1917, though it was later published and reviewed by Lhermitte in 1920 and 1924 1
• The classic presentation involves a sudden electric shock-like sensation transmitted down the spine in a cervico-caudal direction during neck flexion 1, 2
• A variant called "reverse Lhermitte's phenomenon" occurs when the sensation is triggered by neck extension rather than flexion 2
• The sensation may radiate into the extremities and is typically transient 3

Pathophysiology

• Lhermitte's sign is caused by distortion and demyelination of cervical dorsal column sensory axons 4
• It represents a form of myelopathy affecting the cervical spinal cord 1
• In radiation-induced cases, the anterior spinal cord structures such as the spinothalamic tract may be the primary target 5
• Long-term doses of pyridoxine (vitamin B6) as low as 100 mg/day have been associated with Lhermitte's sign, suggesting an effect on the spinal cord 6

Common Etiologies

• Multiple sclerosis (most common cause) 4
• Cervical spondylotic myelopathy 4
• Cisplatin and other platinum-based chemotherapy neurotoxicity 1, 3
• Cervical radiation injury, particularly after head and neck radiotherapy 5
• Neck trauma 4
• Spinal cord compression from tumors (epidural, subdural, or intrinsic) 4
• Vitamin B6 (pyridoxine) toxicity at doses of 100 mg/day or higher 6
• TNF antagonist therapy (may cause demyelinating diseases with Lhermitte's symptom) 6

Diagnostic Approach

• MRI of the brain or spinal cord is the preferred imaging modality when Lhermitte's sign is detected 6, 7
• CT can be used as an alternative if MRI is contraindicated 7
• Evaluate for other upper motor neuron signs such as hyperreflexia, spasticity, and weakness 7
• Consider checking vitamin B6 levels if supplementation is suspected as a cause 6
• In patients receiving TNF antagonists, promptly evaluate for demyelinating disease 6

Management

• Treatment should primarily address the underlying cause 3:

  • Discontinuation of causative medications (e.g., platinum-based chemotherapy) 3
  • Reduction of vitamin B6 supplementation if levels are excessive 6
  • Surgical decompression for structural causes of cord compression 7, 4
  • Standard stroke management protocols for vascular causes 7
  • Stopping TNF antagonist therapy if neurological symptoms develop 6

• Symptomatic treatment options include:

  • Carbamazepine and gabapentin (most commonly used agents) 3
  • Neck collar immobilization for cases related to cervical compression 2
  • Non-pharmacological approaches may provide mild to moderate symptomatic improvement 3

Special Considerations

• In patients receiving TNF antagonists who develop Lhermitte's sign, treatment should be stopped immediately and specialist advice sought 6
• Patients with a history of head and neck radiotherapy should be monitored for this phenomenon, particularly with IMRT which can deliver a gradient of radiation dose to the spinal cord 5
• Long-term follow-up is recommended in idiopathic cases to rule out developing multiple sclerosis 2
• Vitamin B6 supplementation should not exceed 100 mg/day to avoid neurological complications 6

Prognosis

• Prognosis depends on the underlying cause 3
• Medication-induced Lhermitte's sign typically resolves with cessation of the causative agent 3
• In radiation-induced cases, symptoms may persist but can improve over time 5
• When caused by structural lesions, resolution depends on successful treatment of the primary pathology 4