What is the diagnosis and treatment for a patient with paresthesia (tingling sensations) in the lower legs, particularly the left leg, for 2 months, and abnormal sensations in the arms for 6 months, along with back tingling?

Diagnostic Approach to Chronic Progressive Paresthesias

This patient's presentation of progressive paresthesias affecting multiple limbs over 6 months, with asymmetric lower extremity involvement and back tingling, requires urgent evaluation for demyelinating disease, particularly multiple sclerosis, followed by assessment for metabolic neuropathy, structural spinal pathology, and plexopathy.

Key Diagnostic Considerations

Red Flags Requiring Urgent Workup

• Progressive symptoms over 6 months with multifocal distribution (arms, legs, back) suggest central nervous system pathology rather than isolated peripheral neuropathy 1
• Asymmetric lower extremity involvement (left worse than right) is atypical for length-dependent peripheral neuropathy and raises concern for demyelinating disease or structural lesions 1
• Back tingling combined with limb paresthesias may indicate spinal cord involvement (myelopathy) 1

Primary Differential Diagnosis

Multiple Sclerosis/Demyelinating Disease:

• Presents with multifocal neurologic symptoms affecting different body regions over time 1
• Paresthesias are common presenting symptoms, often asymmetric 1
• MRI of brain and spine with contrast is essential to identify demyelinating lesions 1

Metabolic/Toxic Neuropathy:

• Diabetic peripheral neuropathy typically presents with bilateral, symmetric "stocking-glove" distribution starting distally in feet 2, 3
• Vitamin B12 deficiency causes paresthesias but usually symmetric and distal 4
• This patient's asymmetric, multifocal pattern makes pure metabolic neuropathy less likely 2

Structural Spinal Pathology:

• Cervical or thoracic spinal stenosis, cord compression, or myelopathy can cause upper and lower extremity symptoms with back involvement 1
• Lumbosacral plexopathy causes lower extremity symptoms but would not explain arm involvement 1

Essential Diagnostic Workup

Immediate Neuroimaging (First Priority)

MRI of cervical and thoracic spine with and without contrast:

• Evaluate for demyelinating lesions, cord compression, myelopathy, or structural abnormalities 1
• Include dedicated sequences through oblique planes if plexopathy suspected 1

Brain MRI with and without contrast:

• Identify periventricular white matter lesions characteristic of multiple sclerosis 1
• Assess for other CNS pathology 1

Laboratory Evaluation

Metabolic screening:

• HbA1c and fasting glucose to exclude diabetic neuropathy 2
• Vitamin B12 level (deficiency causes subacute combined degeneration with paresthesias) 1, 4
• Thyroid function (TSH, free T4) as thyroid disorders can cause neuropathy 1
• Serum calcium, phosphorus, and parathyroid hormone 1

Inflammatory/autoimmune markers:

• Erythrocyte sedimentation rate and C-reactive protein 1
• Antinuclear antibody if vasculitis suspected 1

Neurophysiologic Testing

Nerve conduction studies and electromyography:

• Confirm peripheral neuropathy if present and characterize pattern (axonal vs. demyelinating) 5
• Identify focal entrapment neuropathies (carpal tunnel syndrome affects hands but not legs) 5, 4
• Important caveat: Normal nerve conduction studies do NOT exclude small fiber neuropathy 5

Lumbar puncture (if demyelinating disease suspected):

• Assess for intrathecal antibody production, oligoclonal bands, elevated IgG index 1
• CSF protein and cell count 1

Clinical Examination Priorities

Neurologic Examination Focus

Upper extremity assessment:

• Test for median nerve distribution weakness (LOAF muscles: lateral lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis) to identify carpal tunnel syndrome 5
• Evaluate for upper motor neuron signs (hyperreflexia, spasticity, Hoffman's sign) suggesting myelopathy 1

Lower extremity assessment:

• Assess for asymmetric weakness, sensory loss, and reflex changes 1
• Perform 10-g monofilament testing, pinprick, vibration, and temperature sensation 2
• Check for upper motor neuron signs (Babinski sign, clonus) 1

Spine examination:

• Palpate for tenderness, assess range of motion 1
• Evaluate for sensory level on trunk suggesting spinal cord pathology 1

Management Algorithm

If MRI Shows Demyelinating Lesions:

• Urgent neurology referral for multiple sclerosis evaluation and disease-modifying therapy 1
• Consider high-dose corticosteroids for acute relapse 1

If MRI Shows Spinal Cord Compression:

• Urgent neurosurgical consultation 1
• Timing of intervention depends on severity and progression 1

If Workup Suggests Peripheral Neuropathy:

• Optimize glucose control if diabetic 2, 3
• First-line pharmacologic therapy: pregabalin 150-600 mg/day, duloxetine, or gabapentin for neuropathic pain 2, 3, 6
• Address reversible causes (B12 supplementation if deficient, medication adjustment) 1, 5

If Initial Workup Unrevealing:

• Neurology referral for consideration of small fiber neuropathy testing (skin biopsy), autoimmune neuropathy panel, or paraneoplastic antibodies 5, 4

Critical Pitfalls to Avoid

• Do not attribute multifocal, progressive symptoms to "anxiety" or "stress" without thorough neurologic evaluation 1
• Do not assume diabetic neuropathy without documented diabetes and typical symmetric distal pattern 2, 7
• Do not delay MRI in patients with progressive symptoms, as early diagnosis of demyelinating disease improves outcomes 1
• Do not rely solely on nerve conduction studies, as they miss small fiber neuropathy 5
• Do not overlook vitamin B12 deficiency, which can cause irreversible neurologic damage if untreated 1, 4