**Core Concept**
The patient's condition is likely caused by a cutaneous manifestation of a systemic disorder, specifically a skin manifestation of a coagulation disorder. Warfarin, an oral anticoagulant, inhibits vitamin K-dependent clotting factors, leading to an increased risk of bleeding but also paradoxically inducing skin lesions in some patients.

**Why the Correct Answer is Right**
This patient's symptoms are consistent with warfarin-induced skin necrosis (WISN), a rare but serious complication of warfarin therapy. WISN often occurs within the first few days of starting warfarin, particularly in patients with underlying hypercoagulable states or those with high levels of protein C or S. The skin lesions are thought to be caused by the rapid depletion of protein C, which normally serves as an anticoagulant. The bulla formation and purpura observed in this patient are characteristic of WISN.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not account for the patient's recent switch to warfarin and the temporal relationship between the initiation of warfarin therapy and the onset of skin lesions.

**Option B:** This option is incorrect as it does not consider the patient's underlying medical history and the potential for warfarin-induced skin necrosis.

**Option C:** This option is incorrect as it does not explain the patient's recent change in anticoagulation therapy and the associated skin lesions.

**Option D:** This option is incorrect as it does not account for the patient's specific medical history and the potential for warfarin-induced skin necrosis.

**Clinical Pearl / High-Yield Fact**
WISN is a rare but serious complication of warfarin therapy, particularly in patients with underlying hypercoagulable states or those with high levels of protein C or S. Patients initiating warfarin therapy should be closely monitored for signs of skin necrosis, and alternative anticoagulants should be considered in high-risk patients.

**Correct Answer:** C. Warfarin-induced skin necrosis.