Makindo Medical Notes

Foot drop (weakness of the tibialis anterior muscle) can result from lesions to the common peroneal nerve or the L5 nerve root.

Causes of Foot Drop

Foot drop can be caused by various conditions that affect the nerves or muscles responsible for foot dorsiflexion. Some common causes include:

• Peroneal Nerve Injury: Often due to trauma or compression, such as crossing the legs frequently, prolonged immobilization, or trauma to the fibular head.
• L5 Radiculopathy: Compression or injury to the L5 nerve root, often from a herniated disc, can result in weakness in foot dorsiflexion.
• Charcot-Marie-Tooth Disease: A genetic neuropathy causing progressive muscle weakness, high arches, and foot deformities.
• Stroke: Central nervous system damage from a stroke can cause unilateral weakness, including foot drop.
• Multiple Sclerosis: This autoimmune disease can cause demyelination, leading to various neurological symptoms, including foot drop.
• Motor Neuron Disease (e.g., ALS): Progressive degeneration of motor neurons results in muscle atrophy and weakness.
• Diabetic Neuropathy: Long-standing diabetes can lead to peripheral neuropathy affecting foot muscles.
• Trauma or Surgery: Direct injury to the peroneal nerve from fractures or hip/knee surgery can result in foot drop.

Assessment of Foot Drop

• History: Ask about recent injuries, surgeries, or symptoms of systemic disease (e.g., diabetes, signs of multiple sclerosis, stroke symptoms).
• Physical Examination:
  • Assess muscle strength, particularly dorsiflexion and inversion.
  • Examine for sensory deficits along the dorsum of the foot and leg, which may indicate peroneal nerve or L5 nerve root involvement.
  • Observe for high-arched foot or other deformities (suggestive of Charcot-Marie-Tooth disease) and signs of spasticity or fasciculations (indicative of motor neuron disease).
• Investigations: Tailored to the suspected cause:
  • Electromyography (EMG) and Nerve Conduction Studies: To assess nerve function and identify patterns consistent with peripheral or central lesions.
  • Imaging: MRI of the lumbar spine for L5 radiculopathy; brain MRI or CT for suspected stroke; MRI or ultrasound of the affected limb for nerve compression or trauma.
  • Genetic Testing: In cases of suspected hereditary neuropathy (e.g., Charcot-Marie-Tooth disease).
  • Blood Tests: For underlying conditions, such as HbA1c for diabetes or other markers if a systemic cause is suspected.

Foot Drop Differential Diagnosis and Management