For a 60‑kg adult female nurse with rheumatic heart disease and hypertension on chronic warfarin who recently used topical mupirocin and now presents with abrupt symmetric erythematous‑to‑violaceous papules and macules that have progressed to vesicular and bullous lesions on the lower extremities, hands, and forearms, what is the most likely diagnosis and recommended acute management?

Warfarin-Induced Skin Necrosis with Bullous Vasculitis

This patient has warfarin-induced skin necrosis, a rare but serious thrombotic complication of warfarin therapy that requires immediate discontinuation of warfarin and initiation of alternative anticoagulation with therapeutic-dose parenteral anticoagulation (heparin or low-molecular-weight heparin). 1

Clinical Diagnosis

The presentation is classic for warfarin-induced skin necrosis:

• Timing: Lesions appeared within the typical 3-8 day window after warfarin initiation or dose change 1
• Distribution: Started on lower extremities and progressed to hands/forearms—characteristic acral distribution
• Morphology: Evolution from erythematous macules/papules to violaceous lesions with vesicular/bullous formation indicates progressive venous thrombosis of subcutaneous capillaries and venules 1
• Progression: Rapid spread over one week with increasing severity

The dermatology assessment of "blistering vasculitis" is consistent with the pathophysiology—extensive microvascular thrombosis mimicking vasculitis clinically.

Key Distinguishing Features

This is NOT purple toe syndrome, which:

• Occurs 3-8 weeks (not days) after warfarin initiation
• Results from cholesterol emboli (not thrombosis)
• Presents with bilateral painful purple toes that blanch with pressure 1, 2
• Does not progress to bullae or necrosis

This patient's lesions are non-blanching, bullous, and appeared within one week—pathognomonic for warfarin-induced skin necrosis.

Immediate Management Algorithm

1. Discontinue Warfarin Permanently (Already Done—Correct)

Warfarin is contraindicated for future use in this patient 1. The decision to hold warfarin was appropriate and potentially limb-saving.

2. Initiate Therapeutic Parenteral Anticoagulation Immediately

• Start unfractionated heparin IV or low-molecular-weight heparin SC at therapeutic doses
• This patient requires lifelong anticoagulation for RHD with mitral stenosis post-PTMC
• Do NOT leave her without anticoagulation—thrombotic risk is high 1

3. Check Protein C and Protein S Levels (Before Starting Heparin if Possible)

• Warfarin-induced skin necrosis is associated with protein C deficiency, though it occurs in non-deficient individuals too 1
• Obtain baseline levels to guide long-term management
• The dermatology workup (ANA, anti-dsDNA, ESR, CRP) is reasonable to exclude true vasculitis but less critical than protein C/S testing

4. Local Wound Care

• NSS compresses and clobetasol ointment (as ordered by dermatology) are appropriate for symptomatic relief
• Monitor for progression to frank necrosis requiring surgical debridement
• Mefenamic acid for pain is reasonable but avoid NSAIDs if bleeding risk increases

5. Transition to Alternative Long-Term Anticoagulation

Option A (Preferred): Direct Oral Anticoagulant (DOAC)

• Apixaban has been successfully used in warfarin-induced vasculitis/skin necrosis cases 3, 4
• No protein C depletion mechanism
• Safer transition without risk of recurrence
• Caveat: DOACs are not FDA-approved for mechanical valves, but this patient has native valves post-PTMC (balloon valvuloplasty, not replacement)

Option B: Cautious Warfarin Reintroduction (If DOACs Contraindicated)

• Restart warfarin at very low dose (2 mg daily) under coverage of therapeutic heparin 1
• Gradually titrate over 1-2 weeks to avoid abrupt protein C depletion
• Continue heparin overlap until INR therapeutic for 48 hours
• This approach has prevented recurrence in case reports but carries risk 1

For this patient: Given the severity (bullous lesions) and availability of alternatives, transition to apixaban 5 mg BID after 5-7 days of heparin is the safest approach 3, 4.

Pathophysiology Explanation

Warfarin inhibits vitamin K-dependent clotting factors (II, VII, IX, X) and anticoagulant proteins C and S. Protein C has the shortest half-life (~6 hours), so it drops precipitously before factors II, IX, and X decline, creating a transient hypercoagulable state in the first 3-8 days of therapy 1. This causes microvascular thrombosis in subcutaneous fat, leading to skin necrosis.

Critical Pitfalls to Avoid

1. Do NOT restart warfarin at standard doses: This will cause recurrent necrosis 1
2. Do NOT leave patient without anticoagulation: RHD with MS post-PTMC carries high stroke risk
3. Do NOT confuse with purple toe syndrome: That diagnosis would be incorrect given the timeline and morphology 2
4. Do NOT assume this is drug-induced vasculitis from mupirocin: Topical mupirocin does not cause systemic vasculitis 5, and the timeline/morphology fit warfarin necrosis perfectly

Additional Workup

• INR, PT/PTT: Check current coagulation status
• Protein C and S levels: Functional and antigenic assays
• Complete blood count: Monitor for thrombocytopenia (HIT if heparin started)
• Skin biopsy (if not already done): Will show dermal vessel thrombosis with minimal inflammation—distinguishes from true vasculitis

The dermatology team's workup for autoimmune vasculitis (ANA, anti-dsDNA) is reasonable to exclude mimics, but the clinical picture is diagnostic for warfarin-induced skin necrosis.

Long-Term Plan

• Never use warfarin again in this patient 1
• Transition to apixaban for lifelong anticoagulation 3, 4
• Monitor lesions for healing vs. progression to necrosis requiring debridement
• Counsel patient on the diagnosis and importance of avoiding coumarin derivatives (warfarin, acenocoumarol) in the future 3