What is the appropriate evaluation and management of a patient presenting with Lhermitte's sign, potentially associated with multiple sclerosis, cervical spondylosis, vitamin B12 deficiency, or radiation-induced myelopathy?

Lhermitte's Sign: Evaluation and Management

When a patient presents with Lhermitte's sign (electric shock-like sensation down the spine with neck flexion), immediately obtain MRI of the cervical and thoracic spine without and with contrast to identify the underlying pathology, as this symptom indicates dorsal column dysfunction requiring urgent evaluation to prevent irreversible neurological damage. 1

Initial Diagnostic Approach

Immediate Imaging

• MRI of the entire spine (cervical and thoracic) without and with IV contrast is the gold standard first-line test for evaluating Lhermitte's sign, as it provides superior visualization of the spinal cord parenchyma, demyelinating lesions, compressive pathology, and inflammatory processes. 1
• MRI should include sagittal and axial T1-weighted, T2-weighted, STIR/short-tau inversion recovery sequences, and post-gadolinium T1-weighted images to detect enhancement patterns. 1
• Add diffusion-weighted imaging if spinal cord ischemia is suspected, as it can show signal changes earlier than T2-weighted sequences. 1

Critical Laboratory Evaluation

Obtain the following blood tests immediately alongside imaging:

• Vitamin B12 level and methylmalonic acid (B12 deficiency is a treatable cause that can present with isolated Lhermitte's sign). 2, 3
• Complete blood count with peripheral smear (to assess for macrocytic anemia suggesting B12 deficiency). 4
• HIV, RPR (syphilis), hepatitis B and C serology (infectious myelopathies). 1
• Thyroid function tests, morning cortisol. 1

Differential Diagnosis by MRI Findings

Multiple Sclerosis Pattern

Look for multiple discrete focal lesions that are:

• Small (≥3 mm), cigar-shaped on sagittal views, wedge-shaped on axial views. 1
• Located peripherally in lateral or posterior columns, covering <2 vertebral segments. 1
• May show T1 hypointensity at higher field strengths. 1
• Nodular or open-ring enhancement if active (enhancement typically lasts 2-8 weeks). 1
• If spinal cord lesions are found, obtain brain MRI to assess for dissemination in space (periventricular, juxtacortical, infratentorial lesions). 1, 5
• Perform lumbar puncture for oligoclonal bands and CSF analysis if MS is suspected. 5

Cervical Spondylotic Myelopathy Pattern

Identify:

• Spinal cord compression from disc-osteophyte complexes or ligamentum flavum hypertrophy. 1
• T2 hyperintensity in the cord at the level of stenosis (indicates myelomalacia and poor surgical prognosis). 1
• Characteristic "pancake-like" enhancement immediately at and below stenosis level. 1
• Even with mild compression, check vitamin B12 levels, as combined pathology can cause disproportionate symptoms. 2

Vitamin B12 Deficiency Pattern

Suspect when:

• Selective involvement of posterior and lateral columns (subacute combined degeneration). 1
• Longitudinally extensive T2 hyperintensity in dorsal columns. 1
• Normal or minimal cord compression with disproportionate high T2 signal changes. 2
• Associated peripheral neuropathy, cognitive dysfunction, or macrocytic anemia. 3

Radiation Myelopathy Pattern

Consider in patients with:

• History of neck/thoracic radiation (typically 6 months to 3 years post-treatment). 6, 7
• T2 hyperintensity and cord swelling at the radiation field level. 1
• May have normal MRI initially despite symptoms. 4

Tumor-Related Pattern

Red flags include:

• Fusiform intramedullary expansion with T2 hyperintensity and enhancement (ependymoma, astrocytoma). 6
• Epidural mass with cord compression (metastasis). 7
• Enhancement persisting >3 months (atypical for MS, suggests tumor or vascular malformation). 1

Neuromyelitis Optica Spectrum Disorder (NMOSD)

Exclude NMOSD before treating as MS, as some MS therapies worsen NMOSD:

• Longitudinally extensive transverse myelitis (≥3 vertebral segments). 1
• Central gray matter involvement ("owl's eye" sign). 1
• Bright spotty lesions on T1 post-contrast. 1
• Test for anti-aquaporin-4 (AQP4) antibodies if this pattern is present. 5

Management Algorithm

If Multiple Sclerosis is Confirmed

• Treat acute relapse with IV methylprednisolone 1000 mg daily for 3-5 days. 5
• Consider plasma exchange if no response to steroids. 5
• Initiate disease-modifying therapy promptly if high-risk features present (multiple brain lesions, oligoclonal bands). 5

If Cervical Spondylosis is Identified

• Neurosurgical consultation for anterior cervical decompression if progressive myelopathy or significant cord compression. 2
• Check and replace vitamin B12 if deficient, even with surgical pathology present. 2

If Vitamin B12 Deficiency is Found

• Immediate vitamin B12 replacement therapy (typically 1000 mcg IM daily for 1 week, then weekly for 4 weeks, then monthly). 3
• Symptoms may improve significantly with replacement alone. 2, 3

If Radiation Myelopathy is Suspected

• Neurology consultation for corticosteroid trial (methylprednisolone 1-2 mg/kg/day). 1
• Consider hyperbaric oxygen therapy in select cases (not guideline-based but used in practice).

If Tumor is Identified

• Urgent neurosurgical consultation for biopsy and/or resection. 6
• Oncology referral for systemic disease evaluation if metastatic. 7

Common Pitfalls to Avoid

• Do not assume MS without excluding B12 deficiency—this is a completely reversible cause that can present identically. 3
• Do not start MS disease-modifying therapy without testing for AQP4 antibodies if longitudinally extensive lesions are present, as this could be catastrophic in NMOSD. 5
• Do not dismiss mild spondylotic changes as the sole cause if T2 signal changes are disproportionate to compression—check B12 levels. 2
• Do not rely on normal MRI to exclude pathology in early radiation myelopathy or post-traumatic cases—clinical correlation is essential. 4
• Do not delay treatment while awaiting CSF results if acute demyelinating syndrome is suspected—start IV methylprednisolone immediately. 5