What causes red swollen feet?

Causes of Red Swollen Feet

Red, swollen feet can be caused by several conditions including diabetic foot infection, Charcot neuro-osteoarthropathy, erythromelalgia, or chronic venous insufficiency, with diabetic foot infection being the most common serious cause requiring prompt intervention. 1

Diabetic Foot Infection

Diabetic foot infection is a common and serious cause of red, swollen feet, particularly in individuals with diabetes mellitus. The International Working Group on the Diabetic Foot (IWGDF) provides clear diagnostic criteria:

Diagnostic Signs:

• At least two of the following local signs:
  • Local swelling or induration
  • Erythema >0.5 cm around a wound
  • Local tenderness or pain
  • Local warmth
  • Purulent discharge 1

Classification of Severity:

1. Mild infection: Involves only skin/subcutaneous tissue with erythema <2 cm
2. Moderate infection: Involves deeper structures or erythema ≥2 cm
3. Severe infection: Accompanied by systemic inflammatory response (fever >38°C or <36°C, heart rate >90/min, respiratory rate >20/min, abnormal WBC) 1

Charcot Neuro-osteoarthropathy

This is frequently overlooked in patients with diabetes and neuropathy. The 2023 IWGDF guidelines emphasize that Charcot should always be considered in a person with diabetes with neuropathy and a hot swollen foot, even when infection or ulceration is present. 1

Key Features:

• Red, hot, swollen foot in a patient with diabetic neuropathy
• May occur with or without ulceration/infection
• Often misdiagnosed initially
• MRI shows bone marrow edema without fractures in early stages 1

Erythromelalgia

A less common but important cause of red, hot, painful feet:

Characteristic Features:

• Episodes of severe burning pain
• Striking redness and warmth of skin
• Symptoms triggered by heat or activity
• Relief obtained by cooling the affected part 1, 2

Types:

• Primary: Often begins in childhood, may be hereditary
• Secondary: Associated with thrombocythemia, collagen-vascular diseases, diabetes mellitus, peripheral neuropathy 2, 3

Chronic Venous Insufficiency ("Red Legs")

A chronic inflammatory condition often misdiagnosed as cellulitis:

Key Features:

• Bilateral involvement
• Associated with chronic edema
• Does not respond to antibiotics
• Often accompanied by sensation of heaviness 4, 5

Diagnostic Approach

1. Assess for diabetic neuropathy: Test for sensation loss with monofilament
2. Evaluate for infection: Look for purulent discharge, fever, elevated inflammatory markers
3. Perform probe-to-bone test: If positive in a high-risk patient, suggests osteomyelitis 1
4. Imaging:
   • Plain X-rays for all non-superficial infections
   • MRI when advanced imaging is needed (especially for suspected osteomyelitis or Charcot) 1

Important Distinctions

Condition	Key Distinguishing Features
Diabetic Foot Infection	Presence of ulcer, purulent discharge, positive probe-to-bone test
Charcot Foot	Neuropathy, foot deformity, bone marrow edema on MRI
Erythromelalgia	Episodic symptoms, relief with cooling, burning pain
Chronic Venous Insufficiency	Bilateral involvement, chronic edema, no response to antibiotics

Common Pitfalls

1. Misdiagnosing Charcot as infection: The presence of infection does not preclude underlying Charcot foot 1
2. Overuse of antibiotics: "Red legs" due to venous insufficiency does not require antibiotics 4
3. Missing osteomyelitis: Consider bone infection with any deep or chronic ulcer, especially over bony prominences 1
4. Delayed diagnosis: Erythromelalgia is often unrecognized despite patients seeking medical attention 6

Early recognition and appropriate management of the underlying cause of red swollen feet is crucial to prevent complications such as amputation, chronic pain, and disability.