A 50-year-old man with muscle pain and fever for a month now notes darker colored urine for the past 2 weeks. On physical examination, he has palpable purpuric lesions of his skin. Urinalysis shows hematuria and proteinuria. Serum laboratory findings include mixed cryoglobulinemia with a polyclonal increase in IgG, as well as a high titer of anti-neutrophil cytoplasmic autoantibodies, mainly antimyeloperoxidase (MPO-ANCA, or P-ANCA. A skin biopsy is performed. What pathologic finding is most likely to be observed in this biopsy?