What area is likely to develop paresthesia in a patient (Pt) with back pain radiating to the leg and inability to perform dorsiflexion?

Dorsal Foot and Great Toe Paresthesia

The patient will most likely develop paresthesia in the dorsal aspect of the foot and the big toe, as this presentation of back pain radiating to the leg with inability to dorsiflex indicates L5 nerve root compression, typically from an L5-S1 disc lesion. 1

Neuroanatomical Localization

The clinical presentation described—back pain with leg radiation and loss of dorsiflexion—points specifically to L5 nerve root pathology:

• The L5 nerve root innervates the dorsal aspect of the foot, including the big toe, making sensory loss in this area the characteristic finding for L5 compression. 1
• L5-S1 disc lesions typically compress the L5 nerve root as it exits the neural foramen, producing this specific pattern of neurological deficits. 1
• Foot dorsiflexion and great toe extension are controlled by the L5 nerve root, which aligns with the motor deficit described in this patient. 1, 2

Distinguishing from Other Nerve Root Patterns

It's important to differentiate this from adjacent nerve root compressions:

• S1 nerve root compression produces lateral foot paresthesia and affects plantar flexion (not dorsiflexion), along with loss of ankle jerk reflex. 2, 3
• L4 nerve root pathology affects the medial thigh and knee strength, not foot dorsiflexion. 2
• The inability to dorsiflex specifically excludes S1 pathology, as plantar flexion is primarily controlled by S1, not L5. 1

Clinical Caveat About Dermatomal Patterns

While the dorsal foot and great toe are the expected areas for L5 paresthesia, be aware of significant individual variation:

• Research shows that only 13.3% of patients with surgically proven L5 nerve root compression recorded sensory symptoms on both anterior and posterior L5 dermatome areas. 4
• For pins and needles specifically, only 20.9% of L5 compression patients recorded more than 50% of their symptoms within the classic L5 dermatome. 4
• Despite this variation, the dorsal foot and great toe remain the most reliable clinical indicators for L5 pathology when combined with dorsiflexion weakness. 1

Diagnostic Confirmation

To confirm the diagnosis and localize the lesion:

• MRI of the lumbar spine is the preferred imaging modality, providing superior definition of nerve root pathology at the L5-S1 level. 1, 2
• Electrodiagnostic studies should be performed to differentiate radiculopathy from plexopathy or peripheral nerve lesions. 1, 2
• The combination of motor deficit (dorsiflexion weakness) with sensory symptoms in the dorsal foot distribution provides strong clinical evidence for L5 radiculopathy. 1, 3