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cardio.dvt.warfarin-induced-skin-necrosis.v1

Warfarin-induced skin necrosis (protein C/S deficiency unmasking)

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Phase E variant of cardio.dvt.core.v1 — narrowed to warfarin-induced skin necrosis (WISN), a rare but catastrophic complication of warfarin initiation in patients with underlying protein C / S deficiency (less commonly factor V Leiden, antithrombin, or APS). Inherits diagnostic + DOAC chronic regimen from parent via routing; specializes for emergency reversal pathway, thrombophilia workup, and lifelong warfarin avoidance with DOAC transition. Manifest pointer reuses cardio.dvt.core.v1 manifest. Design-brief pointer reuses parent (WISN-specific differences documented inline). Phenotypes covered: (1) early WISN at warfarin initiation days 3-10 with painful erythematous plaque (pre-necrosis warning) — STAT recognition prevents extension; (2) established WISN with hemorrhagic bullae and full-thickness necrosis on breast / thigh / buttock / abdomen — emergency reversal + surgical debridement; (3) extensive WISN with hemorrhagic shock or limb-threatening necrosis requiring protein C concentrate at hemophilia center; (4) WISN in setting of triple-positive APS (rare paradox — warfarin standard for APS but precipitated WISN — TRAPS Pengo Blood 2018 informs decision-making). Pathophysiology: warfarin transient procoagulant state in first 3-10 days from kinetic mismatch — protein C half-life 6-8h (falls FIRST), factor VII half-life 4-6h (falls early, masquerades as anticoagulation by raising INR), factors IX/X half-life 24-48h, factor II half-life 60-72h (falls LAST); in protein C / S-deficient patient, baseline anticoagulant pool is depleted → warfarin precipitates microvascular thrombosis in dermal venules supplying subcutaneous fat → necrosis. Treatment paradigm: (1) STOP warfarin immediately; (2) vitamin K 5-10 mg IV slow infusion (acts in 6-24h via new protein C synthesis); (3) FFP 2-4 units OR 4F-PCC 25-50 IU/kg for immediate protein C replacement (4F-PCC preferred if HF / renal failure / urgent reversal); (4) bridge AC with therapeutic UFH or LMWH (if no HIT) or fondaparinux; (5) transition to DOAC (apixaban or rivaroxaban) for long-term AC — preferred over warfarin re-challenge to AVOID lifetime recurrence risk; (6) surgical debridement for established necrosis; (7) protein C concentrate (Ceprotin) for severe homozygous protein C deficiency at hemophilia centers; (8) hematology consult mandatory for thrombophilia workup AFTER warfarin washout ≥2 weeks; (9) lifelong warfarin avoidance with medical alert bracelet + EHR allergy banner; (10) cascade family screening for first-degree relatives. Prevention: bridge warfarin initiation with heparin or LMWH for first 5-7 days; never load warfarin ≥10 mg/d (max 5 mg start per Crowther 2003 + ACCP 2016); avoid warfarin entirely in known protein C / S deficiency (use DOAC for long-term VTE management); screen family members of WISN survivors for protein C / S deficiency before any warfarin exposure. Status INTEGRATED. Authored 2026-05-15 by shard-06-cardio-acute as WISN variant.

Entry points (4)

  • symptom
    Painful erythematous indurated plaque on breast / thigh / buttock / abdomen on warfarin day 3-10 — pre-necrosis warning sign; STAT recognition prevents extension
    painful_red_plaque_in_warfarin_initiation_days_3_to_10
  • symptom
    Hemorrhagic bullae or full-thickness skin necrosis on warfarin days 3-10, areas with abundant subcutaneous fat — established WISN; emergent reversal
    hemorrhagic_bullae_or_necrosis_during_warfarin_initiation
  • history
    Warfarin initiated without heparin or LMWH bridge OR with high loading dose ≥10 mg/d in patient with known or suspected protein C / S deficiency
    warfarin_initiation_without_heparin_lmwh_bridge_in_protein_c_or_s_deficient_patient
  • history
    Family history of warfarin-related skin necrosis or thrombophilia (protein C / S deficiency, factor V Leiden) — high pre-test probability for WISN risk on first warfarin exposure
    family_history_warfarin_skin_necrosis_or_protein_c_or_s_deficiency

Required inputs (15)

  • agerequired
    demographic • used at CONTEXT
    Middle-aged women (postmenopausal) at highest WISN risk; age informs DOAC choice and dose adjustment for long-term AC
  • sexrequired
    demographic • used at CONTEXT
    WISN female-predominant (postmenopausal women > men) — modifies pre-test probability and screening priority
  • warfarin_start_date_and_loading_doserequired
    history • used at CONTEXT
    WISN typically days 3-10 of warfarin initiation; high loading dose ≥10 mg/d or absent heparin/LMWH bridge increases risk — both modifiable preventive errors
  • heparin_or_lmwh_bridge_statusrequired
    history • used at CONTEXT
    Concurrent therapeutic-dose heparin or LMWH for ≥5-7 days during warfarin loading covers the protein C kinetic gap → reduces WISN risk; absent or insufficient bridge is a key modifiable risk factor
  • family_history_thrombophilia_or_warfarin_skin_necrosis
    history • used at CONTEXT
    Family history of protein C / S deficiency, factor V Leiden, or unexplained warfarin-related skin necrosis → high pre-test probability for WISN on first warfarin exposure; informs cascade screening
  • prior_vte_or_thrombophilia_workup
    history • used at CONTEXT
    Prior unprovoked VTE or partial thrombophilia workup informs decision to AVOID warfarin entirely and use DOAC for long-term AC
  • inr_at_presentationrequired
    lab • used at INITIAL_WORKUP
    INR at presentation — typically supratherapeutic (≥3.0) when WISN manifests because factor VII (short half-life) has fallen but functional anticoagulation has not yet replaced the lost protein C activity
  • protein_c_activity_off_warfarinrequired
    lab • used at BRANCHING_WORKUP
    Protein C activity assay — must be drawn AFTER warfarin washout (≥2 weeks) for accurate baseline; on-warfarin assays will be falsely low in everyone (warfarin suppresses protein C synthesis); deficient if <55% activity
  • protein_s_activity_off_warfarinrequired
    lab • used at BRANCHING_WORKUP
    Protein S activity assay — same caveat as protein C; deficient if free protein S antigen <60% or activity <55%; second most common WISN-associated thrombophilia
  • factor_v_leiden_genotype
    lab • used at BRANCHING_WORKUP
    Factor V Leiden genetic test — genetic, NOT affected by warfarin; ~5% of European-ancestry population heterozygous; modest WISN risk modifier
  • antithrombin_activity
    lab • used at BRANCHING_WORKUP
    Antithrombin activity — rare but possible WISN-associated thrombophilia; deficient if <60%; affects AC strategy (heparin/LMWH less effective if AT-deficient)
  • aps_workup
    lab • used at BRANCHING_WORKUP
    APS workup (anticardiolipin antibody, lupus anticoagulant, β2-glycoprotein-1) — APS is associated with skin necrosis and procoagulant state; if positive, AC strategy changes (warfarin INR 2-3 traditional but DOAC controversial in triple-positive APS per TRAPS Pengo Blood 2018)
  • creatininerequired
    lab • used at TREATMENT
    eGFR for DOAC dosing (apixaban / rivaroxaban) and LMWH dosing; FFP volume tolerance
  • cbcrequired
    lab • used at INITIAL_WORKUP
    Baseline platelets for AC bleeding risk; Hgb for transfusion if extensive necrosis with hemorrhage
  • skin_lesion_photo_with_demarcation_markerrequired
    imaging • used at INITIAL_WORKUP
    Photo-documentation with anatomic marker (ruler, surgical pen demarcation) for serial monitoring of necrosis extension; baseline within 1 hour of recognition

12-phase flow (11)

  1. 1FRAME
    Warfarin-induced skin necrosis = transient procoagulant state during warfarin first 3-10 days from kinetic mismatch (protein C falls in 6-8h vs factors II/IX/X over 24-72h); STOP warfarin immediately, reverse with vitamin K + FFP/4F-PCC, bridge with non-warfarin AC, hematology consult for thrombophilia workup, plan lifelong warfarin avoidance with DOAC alternative
    inputs: warfarin_start_date_and_loading_dose
    advance: WISN framed as protein C-deficiency unmasking, not generic AC bleeding
  2. 2ENTRY
    Recognize painful erythematous plaque or hemorrhagic bullae on breast / thigh / buttock / abdomen on warfarin days 3-10 — STAT diagnosis to prevent necrosis extension
    inputs: age, sex, heparin_or_lmwh_bridge_status
    advance: WISN suspected and warfarin discontinuation initiated
  3. 3CONTEXT
    Warfarin start date, loading dose, bridging strategy review, family history of thrombophilia or warfarin complications, prior VTE workup
    inputs: warfarin_start_date_and_loading_dose, heparin_or_lmwh_bridge_status, family_history_thrombophilia_or_warfarin_skin_necrosis, prior_vte_or_thrombophilia_workup
    advance: context complete
  4. 4RED_FLAGS
    Extensive skin necrosis requiring debridement / amputation; hemorrhagic shock from bullae rupture; concurrent VTE progression off-warfarin; protein C activity confirmed severely deficient (<30%) suggesting homozygous deficiency or acquired severe depletion
    inputs: inr_at_presentation, cbc
    actions: le_edema
    advance: extent of necrosis quantified and bridge AC initiated
  5. 5INITIAL_WORKUP
    STAT skin lesion photo with demarcation, INR, CBC, BMP, type and crossmatch; consider skin biopsy (small-vessel thrombosis confirms WISN); start IV vitamin K 5-10 mg + FFP 2-4 units OR 4F-PCC 25-50 IU/kg per protocol; surgical / dermatology consult emergent
    inputs: inr_at_presentation, cbc, creatinine, skin_lesion_photo_with_demarcation_marker
    actions: panel.cardiac, panel.renal, panel.coag, panel.cbc
    advance: reversal initiated and consults activated
  6. 6BRANCHING_WORKUP
    Thrombophilia workup AFTER warfarin washout (≥2 weeks): protein C activity, protein S activity (free antigen + activity), factor V Leiden genotype, antithrombin activity, APS panel (anticardiolipin + lupus anticoagulant + β2-glycoprotein-1), homocysteine; skin biopsy with histopathology if not already done
    inputs: protein_c_activity_off_warfarin, protein_s_activity_off_warfarin, factor_v_leiden_genotype, antithrombin_activity, aps_workup
    advance: thrombophilia diagnosis confirmed and lifetime AC strategy documented
  7. 7RISK_STRATIFICATION
    HAS-BLED for AC bleed risk during DOAC long-term; assess extent of established necrosis (small lesion vs limb-threatening); decision: lifetime DOAC for protein C / S deficiency vs warfarin re-challenge with rigorous bridging (rare, only if DOAC contraindicated)
    inputs: cbc, creatinine
    actions: calc.has_bled, calc.ckd_epi_2021
    advance: AC duration + agent + lifetime warfarin avoidance plan documented
  8. 8TREATMENT
    STOP warfarin immediately; vitamin K 5-10 mg IV (acts in 6-24h via new protein C synthesis); FFP 2-4 units OR 4F-PCC 25-50 IU/kg for immediate protein C replacement; bridge AC with therapeutic-dose UFH or LMWH (if no HIT), or fondaparinux; transition to DOAC (apixaban or rivaroxaban — preferred long-term to AVOID warfarin re-challenge); surgical debridement for established necrosis; skin grafting for large lesions; protein C concentrate (rare, severe cases at hemophilia centers)
    inputs: inr_at_presentation, creatinine
    advance: reversal complete and bridge AC running with definitive long-term plan documented
  9. 9DISPOSITION
    ICU if extensive necrosis or hemorrhagic shock; surgical floor for debridement; hematology consult for thrombophilia workup and lifetime AC plan; dermatology for wound care; document EHR allergy / intolerance for WARFARIN
    advance: unit + consults assigned + EHR allergy banner active
  10. 10MONITORING
    Serial skin photos with demarcation q4-12h until stable; daily CBC + BMP; weekly INR if any warfarin remaining (should be off); PTT if on UFH bridge; bleed surveillance; infection surveillance for necrotic wound; pain control
    inputs: cbc, creatinine
    actions: panel.cardiac, panel.cbc
    advance: necrosis demarcated and not extending
  11. 11FOLLOWUP
    Hematology long-term follow-up; thrombophilia results review at 4 weeks; ≥3 mo AC for VTE indication (longer if ongoing risk); LIFELONG warfarin avoidance education with medical alert bracelet and EHR allergy banner; cascade family screening for protein C / S deficiency; pregnancy planning if applicable (DOAC contraindicated in pregnancy → LMWH for VTE in pregnancy with protein C / S deficiency)
    advance: lifelong avoidance education + family screening + AC plan finalised