What are the likely causes, evaluation, and management for burning pain in the fourth and fifth toes of the left foot?

Burning Pain in the 4th and 5th Toes: Likely Causes and Management

The burning pain in your left 4th and 5th toes most likely represents either Morton's neuroma (intermetatarsal nerve compression) or small fiber neuropathy, and you should start with conservative measures including proper footwear, metatarsal padding, and NSAIDs while being evaluated for underlying causes like diabetes.

Primary Diagnostic Considerations

The lateral forefoot location (4th and 5th toes) narrows the differential significantly:

Morton's Neuroma (Most Common for This Location)

• Morton's neuroma typically affects the 3rd-4th intermetatarsal space but can involve the 4th-5th space, causing burning pain, numbness, and tingling in adjacent toes 1, 2
• The compression test of the affected web space is quite specific for diagnosis - squeeze the metatarsal heads together while palpating the intermetatarsal space to reproduce symptoms 2
• Look for pain that worsens with tight or high-heeled shoes and improves when walking barefoot 1

Small Fiber Neuropathy

• Burning pain is the hallmark symptom of small fiber neuropathy, which commonly presents in the feet and toes 3, 4
• The American Academy of Neurology recommends testing small fiber function with pinprick and temperature sensation on the toes 5
• Small fiber neuropathy characteristically worsens at night and causes sleep disturbance 6
• Associated with diabetes, HIV, autoimmune diseases, certain medications, or may be idiopathic 3

Erythromelalgia (Less Common but Important)

• Episodes of severe burning pain accompanied by striking redness and warmth of the skin, precipitated by heat or activity 4
• The Mayo Clinic warns that patients often try to cool extremities in ice water, but prolonged immersion in cold water or ice increases risk of tissue damage, ulcers, and disability 7, 5
• Look for visible redness and warmth during symptomatic episodes 7

Essential Clinical Evaluation

History Elements to Obtain

• Determine if pain is constant or episodic, and whether it worsens at night (suggests neuropathy) 6
• Ask about specific descriptors: burning, sharp pains, paresthesias indicate small fiber involvement 5
• Identify triggers: tight shoes, heat, activity, or standing 1, 2
• Screen for diabetes, thyroid disease, autoimmune conditions, alcohol use, and medications 5, 3

Physical Examination

• Perform the intermetatarsal compression test - squeeze metatarsal heads together while palpating between 4th-5th metatarsals to reproduce pain 2
• Test small fiber function with pinprick and temperature sensation on the affected toes 7, 5
• Test large fiber function with 128-Hz tuning fork for vibration 7, 5
• Inspect for visible erythema, warmth, or swelling during symptomatic periods 7
• Check for foot deformities, calluses, or abnormal pressure points 7, 1

Laboratory Workup

• The American Academy of Family Physicians prioritizes hemoglobin A1c or fasting glucose to screen for diabetes, the most common cause of peripheral neuropathy 5
• Test vitamin B12 levels, as deficiency causes sensory neuropathy 5
• Evaluate thyroid function (TSH), as hypothyroidism causes neuropathy 5

Imaging

• Radiographs of the foot are only necessary if Ottawa rules are positive (to exclude fracture) 7, 5
• Ultrasound can identify Morton's neuroma size and confirm diagnosis if clinical suspicion is high 7, 2
• MRI is not indicated as first-line imaging for chronic foot pain 7

Treatment Algorithm

First-Line Conservative Management (Start Immediately)

For Suspected Morton's Neuroma:

• Avoid tight-fitting or high-heeled shoes - this is critical 1
• Apply metatarsal pad or metatarsal bar to off-load pressure from the affected intermetatarsal space 1
• Use more cushioned insoles to reduce pressure 1
• NSAIDs (oral or topical) for pain relief and inflammation reduction 5, 8
• Consider toe spreader to separate metatarsal heads 1

For Suspected Neuropathy:

• If diabetes is confirmed, optimize glucose control - this is disease-modifying 7
• The American Academy of Neurology recommends pregabalin, duloxetine, or gabapentin as initial pharmacologic treatments for neuropathic pain 7
• Topical treatments can be used as first-line therapy 7
• Immediate cessation of any triggering substance (alcohol, certain medications) 5

For Suspected Erythromelalgia:

• Avoid ice or water immersion, or limit to 10 minutes, 4 times daily maximum 7
• Elevate extremities during symptomatic episodes 7
• Aspirin is effective for patients with associated thrombocythemia 7
• Engage in usual lifestyle while minimizing triggers (heat, prolonged standing) 7

When to Escalate Care (6-8 Weeks)

• Refer to podiatric foot and ankle surgeon if no improvement occurs within 6-8 weeks of appropriate conservative treatment 5, 8
• For Morton's neuroma: surgical excision produces dramatic pain relief when conservative measures fail 2
• For severe, refractory, or disabling neuropathic pain, refer to pain rehabilitation center for multidisciplinary approach 7

Critical Pitfalls to Avoid

• Do not assume all toe burning is neuropathy - Morton's neuroma is a mechanical problem requiring different treatment 2
• Avoid corticosteroid injections near tendons due to rupture risk 5, 8
• Do not allow patients to continuously immerse feet in ice water despite their desire for relief - this causes tissue damage 7, 5
• Do not prescribe opioids for neuropathic pain - lack of long-term benefit with significant harms 6
• Standard nerve conduction studies will be normal in small fiber neuropathy, so negative testing does not exclude the diagnosis 3