Violaceous and ulcerated plaque following a cesarean section-quiz case.

A 27-year-old woman with a painful, reddish-blue (livedoid) skin area showing small ulcerations on the lower abdomen (Figure 1) was examined. The lesion appeared a few centimeters above the inconspicuous, vertically oriented scar 4 weeks after a cesarean section. A regimen of systemic antibiotics had not been successful. Her medical records revealed a problem with excess weight (body mass index 40 [calculated as weight in kilograms divided by height in meters squared]) and a smoking habit. Laboratory test findings were unrevealing, except for increased antinuclear antibody level (1:160) and a slightly elevated parathyroid hormone level (calcium, phosphate, and vitamin D were within normal levels), which both returned to normal within 6 months. Prothrombotic factors (cryoglobulins and anticardiolipin antibodies) were negative. A biopsy was obtained from a central, nonulcerated region and analyzed with hematoxylin-eosin and CD31 staining (Figure 2 and Figure 3). What is your diagnosis?