What should I be concerned about if one foot is cold and the other is warm and perfused?

Unilateral Cold Foot: Critical Differential Diagnosis

A unilateral cold foot with the contralateral foot warm and well-perfused is a vascular emergency until proven otherwise—acute arterial occlusion must be excluded immediately as this threatens limb viability within hours. 1

Immediate Life-Threatening Concerns

Acute Limb Ischemia (Primary Concern)

• Assess for the "6 P's" immediately: Pain, Pallor (or purple discoloration), Pulselessness, Paresthesias, Paralysis, and Poikilothermia (coldness). 1
• Check pedal pulses on both feet: Absent pulses with purple discoloration and coldness strongly suggest arterial occlusion requiring emergent intervention. 1
• Evaluate pain severity: Severe pain out of proportion to physical findings indicates critical ischemia. 1
• Test motor function: Any weakness or paralysis indicates advanced ischemia requiring immediate vascular surgery consultation—this is limb-threatening. 1
• Measure ankle-brachial index (ABI): ABI <0.4 indicates critical ischemia; ABI <0.5 warrants urgent vascular imaging. 1, 2
• Identify embolic source: Check for atrial fibrillation or other cardiac sources, as embolism is a common cause of acute arterial occlusion. 1

Critical pitfall: Do not delay vascular surgery consultation waiting for "demarcation"—in acute ischemia, hours matter for limb salvage. 1

Frostbite (Environmental Exposure)

• Consider if there is history of cold exposure: Frostbite causes unilateral coldness if only one extremity was exposed. 3
• Remove jewelry and constricting materials immediately from the affected extremity to prevent compartment syndrome as tissue thaws. 3
• Do NOT rewarm if any risk of refreezing exists: Repeated freeze-thaw cycles cause worse tissue damage than delayed rewarming. 3, 1
• If concurrent hypothermia is present, rewarm the core before treating frostbite—moderate to severe hypothermia takes priority. 3, 1
• Rapid rewarming protocol: Immerse in warm water at 37-40°C (98.6-104°F) for 20-30 minutes if rewarming is safe and appropriate. 3, 1

Secondary Differential Diagnoses

Charcot Neuro-Osteoarthropathy (In Diabetics)

While Charcot typically presents with a warm foot, it must be considered in the differential:

• Classic presentation is opposite: A unilateral red, hot, swollen foot in a diabetic with neuropathy suggests active Charcot neuro-osteoarthropathy. 3, 4, 2
• Temperature difference ≥2°C between feet (with the affected foot warmer) suggests active Charcot. 3, 4, 2
• Immediate immobilization required: If Charcot is suspected, initiate knee-high offloading device immediately while completing diagnostic workup. 3, 4, 2

Important caveat: A cold foot in a diabetic is more likely vascular disease than Charcot, but both can coexist. 2

Deep Venous Thrombosis with Phlegmasia

• Phlegmasia cerulea dolens can present with a cold, pulseless extremity due to massive venous thrombosis causing arterial compromise. 3
• This is distinguished from arterial occlusion by severe swelling and cyanotic discoloration. 3

Diagnostic Algorithm

1. Immediate pulse check bilaterally: If absent on cold foot → activate vascular surgery immediately. 1

2. Assess for motor deficits: Any weakness/paralysis → emergent vascular surgery consultation regardless of other findings. 1

3. Obtain ABI if pulses diminished: ABI <0.4 = critical ischemia requiring immediate intervention. 1, 2

4. Rule out environmental exposure: History of cold exposure suggests frostbite; assess for concurrent hypothermia. 3, 1

5. In diabetics with neuropathy: Check temperature difference between feet—but remember a cold foot suggests vascular disease, not Charcot. 3, 2

6. Exclude infection: In diabetics, severe infection can present without typical inflammatory responses (fever, leukocytosis may be absent). 1

Management Priorities

For suspected acute arterial occlusion:

• Obtain urgent vascular surgery consultation immediately—do not delay for imaging if clinical findings suggest critical ischemia. 1
• Time to revascularization directly impacts limb salvage and mortality. 1

For frostbite:

• Protect from further injury: Avoid walking on frozen feet; prevent refreezing at all costs. 3, 1
• Seek prompt medical attention for definitive care and assessment of tissue viability. 3

Critical error to avoid: Do not assume absence of fever or leukocytosis rules out severe infection in diabetic patients—they may not mount typical inflammatory responses. 1