What is the cause of burning numbness and tingling on the dorsum of a patient's left foot?

Burning Numbness and Tingling on the Dorsum of the Left Foot

The most likely cause is compression of the superficial peroneal nerve (or deep peroneal nerve if symptoms are limited to the first web space), though diabetic peripheral neuropathy, lumbar radiculopathy (L5), and peripheral arterial disease must be systematically excluded through focused clinical examination and selective testing. 1, 2

Key Distinguishing Features by Anatomic Distribution

Dorsal foot involvement is NOT typical of diabetic peripheral neuropathy, which characteristically begins on the plantar surface of the toes and forefoot before progressing proximally in a symmetric "stocking" distribution. 3, 2 The isolated dorsal presentation strongly suggests a focal nerve compression rather than systemic neuropathy. 1, 4

Superficial Peroneal Nerve Compression

• Produces numbness and tingling over the dorsum of the foot and toes (excluding the first web space), typically from compression at the fibular tunnel or where the nerve pierces the deep fascia in the distal leg. 1
• Symptoms may worsen with ankle plantarflexion and inversion, and Tinel's sign may be positive along the nerve course in the lateral lower leg. 1

Deep Peroneal Nerve Compression

• Causes numbness isolated to the first web space (between first and second toes) if compressed at the anterior tarsal tunnel beneath the extensor retinaculum. 1
• May be associated with tight footwear or repetitive dorsiflexion activities. 1

L5 Radiculopathy

• Produces dorsal foot numbness but typically includes lateral leg symptoms, foot drop weakness (ankle/toe dorsiflexion), and radiating pain from the lower back or buttock. 1, 4
• Positive straight leg raise test and dermatomal distribution extending beyond just the foot distinguish this from isolated nerve compression. 1

Critical Systematic Evaluation

Immediate Clinical Assessment

Determine the precise sensory distribution by mapping the exact area of numbness—superficial peroneal nerve affects the dorsum broadly (sparing first web space), deep peroneal affects only the first web space, while L5 radiculopathy includes lateral leg and medial dorsal foot. 1, 4

Assess motor function by testing ankle dorsiflexion strength (tibialis anterior—L4/L5), great toe extension (extensor hallucis longus—L5), and ankle eversion (peroneal muscles—L5/S1). Weakness suggests radiculopathy or more proximal nerve involvement rather than isolated sensory nerve compression. 1, 4

Examine for vascular compromise by palpating dorsalis pedis and posterior tibial pulses, as peripheral arterial disease can produce foot numbness, particularly with exertion, though this typically presents with claudication symptoms and coolness rather than isolated burning dysesthesias. 3, 2

Rule Out Systemic Causes

Screen for diabetes even in younger patients with hemoglobin A1c or fasting glucose, as diabetic neuropathy is the most common cause of peripheral neuropathy overall, though the unilateral dorsal presentation makes this less likely. 3, 2, 5

Check vitamin B12 level (especially if patient takes metformin ≥2g daily), thyroid function tests, and comprehensive metabolic panel to exclude nutritional and metabolic causes that produce symmetric distal neuropathy, not isolated dorsal foot symptoms. 2, 5, 4

Perform 10-g monofilament testing on the plantar surface to assess for loss of protective sensation—if plantar sensation is preserved but dorsal sensation is impaired, this strongly favors focal nerve compression over systemic neuropathy. 3, 2

Provocative Testing

Perform Tinel's sign along the superficial peroneal nerve course (lateral lower leg where it pierces the fascia approximately 10-12 cm proximal to the lateral malleolus) and at the anterior tarsal tunnel for deep peroneal nerve. 1

Test ankle inversion with plantarflexion to reproduce symptoms if superficial peroneal nerve compression is suspected, as this maneuver stretches the nerve at its fascial exit point. 1

Diagnostic Algorithm

If Symptoms Are Isolated to Dorsum Without Motor Weakness:

1. Diagnose focal nerve compression clinically and initiate conservative management with activity modification, avoiding tight footwear, and nighttime splinting if symptoms occur at rest. 1
2. Reserve electrodiagnostic studies (EMG/NCS) for cases with atypical features, progressive motor weakness, or failure to improve with 3-6 months of conservative therapy. 3, 1, 2

If Motor Weakness or Radiating Pain Is Present:

1. Consider lumbar spine imaging (MRI) to evaluate for L5 radiculopathy if straight leg raise is positive, weakness is present, or symptoms radiate proximally. 1, 4
2. Refer to neurology for electrodiagnostic studies to localize the lesion and differentiate radiculopathy from peripheral nerve compression. 1, 2

If Bilateral or "Stocking-Glove" Distribution Develops:

1. Pursue full metabolic workup including diabetes screening, B12, thyroid function, complete blood count, and serum protein electrophoresis with immunofixation. 2, 4
2. Recognize that bilateral symmetric progression suggests systemic neuropathy rather than focal compression and requires different management approach. 2, 4

Common Pitfalls to Avoid

Do not assume diabetic neuropathy based solely on diabetes history—diabetic peripheral neuropathy begins plantarly and progresses symmetrically, not in isolated dorsal distribution. 3, 2, 5

Do not order routine foot radiographs unless there is trauma history, inability to bear weight, or point tenderness over bony structures per Ottawa Ankle Rules, as imaging is low-yield for neuropathic symptoms without red flags. 2

Do not overlook spinal stenosis in older patients—neurogenic positional pedal neuritis from lumbar spinal stenosis can produce burning and numbness in the feet that varies with spinal position (worse with extension, better with flexion), and is often misdiagnosed as peripheral neuropathy. 6

Do not delay vascular assessment if pulses are diminished—peripheral arterial disease can produce foot numbness and must be distinguished from neuropathy, particularly if symptoms worsen with walking or improve with rest. 3, 2

Management Based on Etiology

For Focal Nerve Compression (Most Likely):

• Initiate conservative management immediately with avoidance of provocative positions, loose-fitting footwear, and activity modification. 1
• Consider nighttime splinting to maintain neutral ankle position if symptoms occur at rest. 1
• Refer for surgical decompression only if severe symptoms persist despite 3-6 months of conservative therapy or if progressive motor weakness develops. 1

If Diabetic Neuropathy Is Confirmed:

• Optimize glycemic control gradually (avoid rapid HbA1c reduction which can paradoxically worsen symptoms) and initiate first-line neuropathic pain medication with pregabalin, duloxetine, or gabapentin. 3, 5
• Arrange podiatry referral for protective footwear and regular foot care, and perform annual 10-g monofilament testing to monitor progression. 3, 5

If Lumbar Radiculopathy Is Identified:

• Refer to spine specialist or neurosurgery for consideration of epidural steroid injection or surgical decompression if conservative management with physical therapy and NSAIDs fails. 1, 6