What are the causes of leg mottling?

Causes of Leg Mottling

Leg mottling (livedo reticularis) is most commonly caused by impaired peripheral circulation, with the primary etiologies being atherosclerotic peripheral arterial disease, septic shock, venous thrombosis, and various systemic conditions affecting the microcirculation. 1

Vascular Causes

Arterial Causes

• Peripheral Artery Disease (PAD): The most common pathology affecting lower extremity arteries is atherosclerosis, related to risk factors such as family history, smoking, hypertension, diabetes, hyperlipidemia, and obesity 1
• Non-atherosclerotic Arterial Diseases:
  • Popliteal Artery Entrapment Syndrome (PAES) - common in young adults 1
  • External Iliac Artery Endofibrosis (EIAE) - primarily in endurance athletes 1
  • Buerger's Disease (Thromboangiitis Obliterans) - inflammatory vasculitis in smokers 1

Venous Causes

• Deep Vein Thrombosis (DVT): Can cause leg swelling and mottling, with an estimated annual incidence of 5 per 10,000 in the general population 1
• Venous Insufficiency: Chronic venous disease can lead to skin changes including mottling 2

Systemic Causes

Sepsis and Shock States

• Septic Shock: Mottling is a clinical sign of microcirculatory alteration and tissue hypoperfusion 1, 3
  • Higher mottling scores correlate with higher arterial lactate levels and increased mortality 3, 4
  • Mottling score (0-5) based on extension from knees to periphery is a strong predictor of 14-day survival 4

Medication-Related

• Warfarin-Induced Skin Necrosis: Can present with mottling and progress to tissue necrosis, especially in patients with protein C or S deficiency 5
• Drug Reactions: Some medications like diphenhydramine combined with pyrithyldione can cause livedo reticularis and thrombotic purpura 6

Other Systemic Conditions

• Connective Tissue Disorders:
  • Marfan Syndrome (MS) and Loeys-Dietz Syndrome (LDS) can affect vascular systems 1
  • Systemic Lupus Erythematosus, scleroderma, and other connective tissue disorders 1
• Lymphedema: Bier spots (reversible white macules) can appear on the background of mottled skin in lymphedema patients 7
• Neurological Conditions: Tethered cord syndrome can present with skin changes and vascular abnormalities in the lower extremities 1

Clinical Evaluation of Leg Mottling

Physical Examination Findings

• Skin Appearance: Reticular, purplish discoloration of the skin
• Distribution: Often more pronounced in the lower two-thirds of the legs 1
• Associated Signs:
  • Diminished pulses in femoral, popliteal, posterior tibial, and dorsalis pedis arteries in arterial disease 1
  • Edema, pain, and warmth in venous disease 1
  • In sepsis: cool extremities, extended neck veins, crepitations 1

Diagnostic Approach

• Vascular Assessment: Check for pulses, capillary refill time, temperature of extremities 1
• Imaging:
  • CT angiography (CTA) for suspected arterial disease 1
  • Compression ultrasonography for suspected venous thrombosis 1

Red Flags and Urgent Conditions

• Acute Limb Ischemia: Presents with the "6 Ps" - pain, pallor, pulselessness, poikilothermia (coolness), paresthesias, and paralysis 1
• Critical Limb Ischemia: Rest pain, non-healing wounds/ulcers, or gangrene with symptoms present for >2 weeks 1
• Septic Shock: Mottling with hypotension, tachycardia, and elevated lactate levels requires immediate intervention 1, 3
• Warfarin-Induced Skin Necrosis: Can progress rapidly from mottling to tissue necrosis and gangrene 5

Remember that leg mottling is a clinical sign that should prompt thorough evaluation to identify the underlying cause, as early intervention can prevent progression to tissue necrosis, gangrene, or systemic complications.