What are the causes of bilateral foot drop?

Causes of Bilateral Foot Drop

Bilateral foot drop is most commonly caused by peripheral neuropathy, particularly diabetic peripheral neuropathy, but can also result from lumbar spinal disorders, neurological conditions, and systemic diseases that affect the nervous system.

Peripheral Nerve Causes

Diabetic Peripheral Neuropathy

• Most common cause of bilateral foot drop 1
• Results from long-term hyperglycemia causing nerve damage
• Presents with symmetric distal sensory loss and weakness
• Often accompanied by pain, dysesthesias, numbness, and reduced vibration sense 1
• Affects dorsiflexor muscles leading to foot drop

Other Peripheral Neuropathies

• Toxic neuropathies from medications (especially chemotherapeutic agents) 1
• Nutritional deficiencies (particularly vitamin B12) 1
• Heavy metal poisoning (e.g., lead) 1
• Alcohol-related neuropathy
• Hereditary neuropathies (e.g., Charcot-Marie-Tooth disease)

Central Nervous System Causes

Lumbar Spine Disorders

• Lumbar disc herniation (especially at L4/L5 level) 2, 3
• Lumbar spinal stenosis 2
• Degenerative lumbar spine disease 3
• Cauda equina syndrome (often with bowel/bladder involvement)

Brain Lesions

• Bilateral parasagittal lesions affecting leg motor cortex 4, 5
• Brain metastases 4
• Stroke affecting bilateral motor cortex or corticospinal tracts 5
• Multiple sclerosis with bilateral cerebral lesions

Systemic Diseases

Autoimmune Disorders

• Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy)
• Chronic inflammatory demyelinating polyneuropathy (CIDP)
• Vasculitis affecting peripheral nerves
• Autoimmune inner ear disease (can present with bilateral symptoms) 1

Infectious Causes

• Lyme disease (can cause fluctuating bilateral audiovestibular symptoms) 1
• Syphilis (can cause bilateral fluctuating neurological symptoms) 1
• HIV-related neuropathy 1
• Meningitis (infectious, inflammatory, or neoplastic) 1

Metabolic Disorders

• Diabetes mellitus (most common) 1
• Uremia (in end-stage renal disease) 1
• Hypothyroidism
• Porphyria

Trauma-Related Causes

• Significant head trauma 1
• Barotrauma 1
• Bilateral compression of peroneal nerves (e.g., prolonged squatting, leg crossing) 6

Diagnostic Approach

Key History Elements

• Onset (sudden vs. gradual)
• Presence of pain (painful vs. painless) 2
• Associated symptoms (sensory changes, bowel/bladder dysfunction)
• Medical history (diabetes, trauma, prior surgeries)
• Medication history (potential neurotoxic agents)

Physical Examination

• Assess foot dorsiflexion strength bilaterally
• Test sensation (pinprick, vibration, light touch) 1
• Check deep tendon reflexes (ankle reflexes) 1
• Evaluate for foot deformities 1
• Assess pedal pulses for vascular status 1

Diagnostic Testing

• Electromyography and nerve conduction studies to localize lesion 6
• MRI of lumbar spine if radiculopathy suspected 2
• Brain imaging (MRI/CT) if central cause suspected 6, 4
• Laboratory testing for systemic causes (diabetes, vitamin B12, thyroid function)

Clinical Pearls

• Bilateral foot drop without pain should raise suspicion for central nervous system or systemic causes rather than peripheral nerve compression 2
• Diabetic patients require regular foot examinations as they may develop neuropathy and foot drop even with minimal symptoms due to sensory loss 1
• Early intervention for spinal causes of bilateral foot drop may lead to better neurological recovery 2
• Preoperative strength of foot dorsiflexion is the key prognostic factor for recovery in surgical cases 3
• Always consider rare central causes when peripheral causes have been ruled out 4, 5

Remember that bilateral foot drop represents a significant functional disability that can increase fall risk and requires prompt evaluation and management to prevent complications.