Review Question - QID 104235

This patient is presenting with leg pain and a necrotic patch on their leg after starting warfarin (without heparin being given) and is most likely experiencing warfarin-induced skin necrosis. This condition often occurs in patients who have protein C deficiency (a hereditary disorder).

Warfarin-induced skin necrosis presents with pain, bulla formation, and skin necrosis following initiation of warfarin. The major risk factor is protein C deficiency. Warfarin inhibits the production of proteins C/S (anticoagulants) as well as clotting factors IX, X, VII, and II. It depletes proteins C and S first, thus patients may experience a transient hypercoagulable state when starting warfarin (which is why heparin is given until the patient has a therapeutic INR). Patients with protein C/S deficiency are even at greater risk for warfarin skin necrosis given they already have low protein C/S levels. Heparin is used for anticoagulation in these patients.

Figure A displays an example of warfarin-induced skin necrosis of the lower limb with the classic necrotic skin lesion.

Incorrect Answers:
Answer 1: Allergic medication reaction may present with urticaria or edema of the upper airway. Warfarin skin necrosis is not an allergic reaction.

Answer 3: Neisseria meningitidis may cause a purpuric rash when disseminated as well as would present with a fever, hypotension, tachycardia, and adrenal failure.

Answer 4: Septic emboli may be seen in bacterial endocarditis and could present with septic pulmonary emboli in the lungs (cough and fever) or the lower extremities (severe pain).

Answer 5: Superficial vein thrombosis may present with a tender and palpable vein over the lower extremity. This pathology could possibly cause a pulmonary embolism (though it is less likely when compared to a DVT).

Bullet Summary:
Protein C/S deficiency can predispose patients to warfarin skin necrosis.