What are the usual investigations for a patient presenting with very mild Lhermitte's sign?

Investigations for Very Mild Lhermitte's Sign

Magnetic Resonance Imaging (MRI) of the cervical spine and brain is the primary investigation recommended for patients presenting with very mild Lhermitte's sign, as it provides the best visualization of potential cerebellar and spinal cord pathology. 1

Understanding Lhermitte's Sign

Lhermitte's sign is characterized by electric shock-like sensations that travel down the spine and limbs upon neck flexion. Even when mild, this symptom warrants thorough investigation as it typically indicates intrinsic spinal cord pathology, most commonly in the cervical region.

Diagnostic Approach

First-Line Imaging

• MRI of the cervical spine without and with IV contrast: This is the preferred initial imaging modality for assessing potential causes of Lhermitte's sign 1
  • Provides superior visualization of the posterior fossa and spinal cord compared to CT
  • Can detect demyelination, compression, inflammation, or tumors affecting the cervical cord
  • Should include sagittal and axial T2-weighted sequences to evaluate for signal changes in the spinal cord

Additional Imaging Based on Clinical Suspicion

• MRI of the brain: Should be performed if multiple sclerosis or other demyelinating disorders are suspected 1, 2
  • Include FLAIR sequences to detect white matter changes suggestive of demyelination
  • Diffusion-weighted imaging can help assess for acute pathology

Laboratory Investigations

• Vitamin B12 levels: Essential to rule out subacute combined degeneration of the cord, as Lhermitte's sign is a common early symptom in this condition 3
• Complete blood count: To evaluate for anemia which may accompany B12 deficiency
• Anti-glutamic acid decarboxylase (GAD) antibodies: May be considered if an autoimmune etiology is suspected 4

Differential Diagnosis to Consider

Lhermitte's sign can be associated with various conditions:

1. Demyelinating disorders: Multiple sclerosis is the most common cause 2
2. Cervical spondylotic myelopathy: Can present with typical or reverse Lhermitte's phenomenon 5
3. Spinal cord tumors: Intrinsic tumors can rarely present with Lhermitte's sign 6
4. Vitamin B12 deficiency: Leading to subacute combined degeneration 3
5. Post-radiation myelopathy: In patients with history of cervical radiation
6. Infectious/inflammatory conditions: Including herpes zoster affecting cervical roots 7

Variant Forms and Their Significance

Be aware of variant forms of Lhermitte's phenomenon, as they have different pathological significance:

• Typical Lhermitte's sign: Induced by neck flexion, suggests intrinsic spinal cord pathology 2
• Reverse Lhermitte's phenomenon: Induced by neck extension, typically indicates extrinsic compression of the cervical cord 2, 5
• Inverse Lhermitte's phenomenon: Upward moving paresthesia with neck flexion, can be seen with nitrous oxide-induced myelopathy 2

Clinical Pearls and Pitfalls

• Even very mild Lhermitte's sign should not be dismissed, as it may be the presenting symptom of serious pathology like spinal cord tumors 6
• Avoid relying solely on CT imaging, as it has limited value in detecting subtle spinal cord abnormalities 1
• Do not delay MRI evaluation, as early diagnosis of conditions like multiple sclerosis or spinal cord compression can significantly impact treatment outcomes and prognosis
• Remember that Lhermitte's sign may be transient in some conditions (like herpes zoster) but can indicate permanent pathology in others 7

Follow-up Recommendations

• If initial investigations are negative but symptoms persist, consider repeat MRI in 3-6 months
• For patients with very mild symptoms and normal imaging, clinical follow-up is essential to monitor for progression or development of additional neurological symptoms