Case two was, as so many of you rightly identified, a case of warfarin induced skin necrosis.
This is a rare condition but is clearly potentially devastating and is the reason that all patients starting on loading doses of warfarin should receive five days of LMWH.
The mechanism of injury is as follows:
- Warfarin prevents the synthesis of Vitamin K dependent clotting factors – II, VII, IX, X, i.e. 1972.
- However it also impairs synthesis of protein C: a natural anti-coagulant that inhibits factors V and VIII and keeps us from forming clots in an uncontrolled fashion.
- Protein C levels fall more rapidly than the 1972, so there is a brief window where warfarin actually makes you prothrombotic.
- In susceptible patients, e.g. those who are already congenitally protein C or S deficient, or who are very prothrombotic, such as patients with Antiphospholipid syndrome, this window of procoaguability is sufficient for microvascular thrombi to form, leading to tissue damage.
A few pertinent facts for you:
- Uncommon serious complication of oral anticoagulation therapy affecting 0.01-0.1% of patients.
- 85% of reported patients are women and affects typically breasts, buttocks, thighs, and abdomen
- There is initially altered sensation then typical lesion development.
- Well-demarcated erythematous lesion that progresses to bullae formation and full-thickness skin necrosis.
- Areas of erythematous flush may become oedematous and have a dimpled peaud’orange effect.
- The eschar may eventually slough or require extensive surgical debridement.
- Patients at risk are those receiving large, rapidly administered loading doses of warfarin; previous episode; protein C or protein S deficiency; or anti-phospholipid syndrome.
- Vitamin K should be administered in the early stages of lesion development can prevent warfarin-induced skin necrosis. Theoretically FFP, which contains protein C, may help.
- The eschar may eventually slough or require extensive surgical debridement; but despite treatment, approximately 50% of patients ultimately require skin grafting.
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