What are the possible causes, recommended work‑up, and management for a persistent hot or warm sensation in both legs?

Hot or Warm Sensation in Both Legs: Differential Diagnosis and Management

The bilateral hot or warm sensation in both legs most commonly represents either small fiber neuropathy (particularly diabetic neuropathy) or erythromelalgia, and the initial workup should focus on distinguishing between these conditions through assessment of associated symptoms, diabetes screening, and examination for erythema and triggers. 1, 2

Key Diagnostic Considerations

Primary Differential Diagnoses

Small Fiber Neuropathy (Most Common)

• Diabetic peripheral neuropathy is the most common cause of bilateral warm sensations in the legs, particularly in patients with type 2 diabetes 1, 2
• Symptoms characteristically begin distally in the feet and progress proximally in a "stocking-glove" distribution 1
• Patients describe altered temperature perceptions with feet feeling abnormally warm or cold 1
• Additional descriptors include burning pain, "electrical shock" sensations, and uncomfortable tingling (paresthesias) 1
• Pain is characteristically worse at night, often causing sleep disturbance 1
• Up to 50% of diabetic peripheral neuropathy may be asymptomatic initially 2

Erythromelalgia

• Characterized by episodic burning pain with visible redness and warmth of the extremities 3, 2
• Symptoms are triggered by physical activity, warm temperatures, and standing 3
• Relief occurs with cooling and elevation 3
• Hands and feet may be bright red, painful, and hot during episodes 3
• Can be primary (idiopathic) or secondary to myeloproliferative disorders (essential thrombocythemia, polycythemia vera) 3, 2

Critical Distinguishing Features

Bilateral vs. Unilateral Presentation

• Peripheral neuropathic pain is invariably symmetrical and bilateral 1
• Asymmetrical symptoms should prompt investigation for other etiologies including Charcot neuro-osteoarthropathy (in diabetics), infection, gout, or deep venous thrombosis 3
• In diabetic patients with unilateral red, warm, swollen foot, Charcot neuro-osteoarthropathy must be excluded due to risk of fractures, dislocations, and amputation 3

Essential Workup

Initial Laboratory Testing

• Fasting glucose and HbA1c to screen for diabetes mellitus (most common cause) 1
• Complete blood count to evaluate for myeloproliferative disorders if erythromelalgia suspected 3
• Thyroid function, calcium, and renal function if secondary causes suspected 4
• Consider screening for neurotoxic medication exposure, heavy metal poisoning, and alcohol abuse 1, 2

Physical Examination Priorities

• Small fiber function assessment: pinprick and temperature sensation 1
• Large fiber function assessment: vibration perception using 128-Hz tuning fork and 10-g monofilament testing 1
• Inspect for visible erythema during symptomatic episodes (present in erythromelalgia, absent in pure neuropathy) 3
• Assess pedal pulses and consider ankle-brachial index to exclude peripheral arterial disease 1
• Temperature assessment: In diabetic patients, infrared thermometry can measure temperature differences between legs (>2°C difference suggests active inflammation like Charcot) 3

Advanced Testing When Indicated

• Standard nerve conduction studies may be completely normal in small fiber neuropathy, as these only evaluate large myelinated fibers 1
• Quantitative sensory testing can demonstrate elevated thresholds for heat and cold detection in small fiber neuropathy 5
• Skin biopsy showing decreased epidermal nerve fiber density occurs in only a minority of cases 3

Management Approach

For Small Fiber Neuropathy/Diabetic Neuropathy

First-Line Pharmacologic Treatment

• Initiate duloxetine 30 mg daily, titrating to 60 mg daily after one week 1
• Alternative first-line options include pregabalin (starting 75 mg twice daily) or gabapentin (starting 300 mg daily) 1
• These agents achieve ≥50% pain reduction in 38% of patients at optimal dosing 1
• Target HbA1c <7% to slow neuropathy progression 1

Non-Pharmacologic Strategies

• Supervised exercise therapy to improve symptoms 1
• Well-fitted walking shoes or athletic shoes with cushioning to redistribute plantar pressure 1
• Podiatry referral for custom orthotics if needed 1
• Monitor and treat depression and anxiety, as over two-thirds of patients with painful neuropathy develop these comorbidities 1, 2

For Erythromelalgia

Non-Pharmacologic Management (Critical)

• Avoid ice or cold water immersion, or limit to 10 minutes, 4 times daily maximum 3
• Prolonged cooling strategies cause immersion foot, trench foot with swelling, skin ulceration, and infection risk 3, 2
• Avoid powerful fans continuously, as these may cause windburn-equivalent damage 3
• Elevate extremities during symptomatic episodes 3
• Consider swimming instead of running for exercise-induced flares 3

Pharmacologic Treatment

• Topical medications are first-line therapy to suppress pain and redness while causing fewer adverse effects than systemic medications 3
• For secondary erythromelalgia due to myeloproliferative disease, aspirin is first-line systemic therapy 3
• Other systemic medications may be considered for refractory cases 3
• Referral to comprehensive pain rehabilitation center for severe, refractory, or disabling cases 3

Common Pitfalls to Avoid

• Failing to screen for diabetes in patients presenting with bilateral warm leg sensations, as diabetic neuropathy is the most common etiology 1, 2
• Not considering non-diabetic causes of neuropathy even in patients with diabetes, including neurotoxic medications, heavy metal poisoning, and vasculitis 1, 2
• Allowing patients to use excessive cooling strategies (prolonged ice water immersion, powerful fans) which can cause tissue damage and worsen outcomes 3, 2
• Missing Charcot neuro-osteoarthropathy in diabetic patients with unilateral presentation, which requires immediate immobilization to prevent devastating complications 3
• Overlooking myeloproliferative disorders as a cause of erythromelalgia, which requires specific treatment with aspirin 3
• Not addressing psychological comorbidities (depression, anxiety) which significantly impact quality of life and treatment outcomes 1, 2