A patient who had a femur fracture one month ago now presents with purpuric skin lesions; what is the most likely cause and what immediate management steps should be taken?

Warfarin-Induced Skin Necrosis Following Femur Fracture

The most likely diagnosis is warfarin-induced skin necrosis, and immediate management requires discontinuing warfarin, administering vitamin K, replenishing vitamin K-dependent factors with fresh frozen plasma or prothrombin complex concentrate, and switching to heparin for ongoing anticoagulation. 1

Clinical Context and Diagnosis

The timing is pathognomonic: purpura appearing one month after a femur fracture strongly suggests warfarin-induced skin necrosis in a patient who was likely started on anticoagulation for venous thromboembolism (VTE) prophylaxis. 1

• Typical onset occurs 3-8 days after warfarin initiation, though presentation can extend beyond this window 1
• Post-operative hip fracture patients have a VTE incidence of 1.6% in-hospital and 8.2% at three months, making anticoagulation common in this population 2
• Lesions characteristically appear on fatty areas (breasts, thighs, buttocks) and progress from petechiae to purpuric patches, hemorrhagic bullae, and eschar formation 1

The pathophysiology involves protein C depleting faster than factors II, IX, and X during warfarin initiation, creating a transient hypercoagulable state with extensive thrombosis of venules and capillaries within subcutaneous fat. 1, 3

Immediate Management Protocol

Step 1: Discontinue Warfarin and Reverse Anticoagulation

• Stop warfarin immediately 1
• Administer vitamin K to allow reversal within 24 hours 1, 4
• Replenish vitamin K-dependent factors using fresh frozen plasma (FFP) or 4-factor prothrombin complex concentrate (PCC) 1
• PCC is reserved for extreme cases requiring urgent reversal, while vitamin K with FFP is the standard approach 4

Step 2: Initiate Alternative Anticoagulation

• Switch to heparin or low molecular weight heparin (LMWH) for continued anticoagulation if needed for the underlying thrombotic condition 1
• This is critical because the femur fracture itself carries ongoing VTE risk requiring prophylaxis 2

Step 3: Wound Management

• Document affected areas on a body map and assess extent of necrosis 1
• Perform surgical debridement of necrotic tissue as needed 1
• Provide appropriate wound care to prevent secondary infections 1
• Consider skin grafting for extensive areas of necrosis 1

Risk Factors and Prevention

Protein C and S deficiency is strongly associated with warfarin-induced skin necrosis, though it also occurs in patients without these deficiencies. 1, 3 Additional risk factors include:

• Middle-aged, perimenopausal women with VTE 1
• Large loading doses of warfarin 1
• Patients with heparin-induced thrombocytopenia transitioning to warfarin 1

Long-Term Anticoagulation Strategy

If anticoagulation must continue, heparin or LMWH is the preferred alternative. 1 If warfarin must be restarted due to clinical necessity:

• Begin with a very low dose (2 mg daily) 1
• Provide concurrent therapeutic-dose parenteral anticoagulation (heparin or LMWH) as a bridge 1, 3
• Gradually increase warfarin dose over several weeks to avoid abrupt protein C depletion 1, 3

Critical Pitfalls to Avoid

• Failing to test for protein C and S deficiencies increases morbidity and mortality risk 1
• Inadequate wound care leading to secondary infections significantly worsens outcomes 1
• Restarting warfarin without appropriate precautions (low dose with heparin bridge) can precipitate recurrent necrosis 1
• Delaying surgical debridement allows progression of tissue necrosis 1

Differential Considerations

While warfarin-induced skin necrosis is most likely given the timing, briefly consider:

• Peripheral arterial disease causing ischemia, though this would not explain acute purpura 5
• Cellulitis or infection, which presents with erythema, warmth, and tenderness rather than purpura 5
• Thrombotic thrombocytopenic purpura (TTP), though this would present with systemic symptoms including hemolytic anemia and thrombocytopenia 6

The clinical scenario of purpura developing weeks after femur fracture in a patient likely on warfarin makes warfarin-induced skin necrosis the diagnosis until proven otherwise, requiring immediate reversal and alternative anticoagulation. 1