Glomerular Diseases USMLE Step 1 Practice Question

A 45-year-old woman with a 10-year history of hepatitis C infection presents to the emergency department with a 2-week history of lower extremity palpable purpura, polyarthralgia, and gross hematuria. She reports malaise and weight loss over the past month. Physical examination reveals BP 146/92 mmHg, palpable purpura on both shins and calves, and mild knee joint swelling bilaterally. Laboratory findings show: serum creatinine 1.8 mg/dL (baseline 0.8), urinalysis with 3+ proteinuria, dysmorphic RBCs, and RBC casts; serum C3 normal at 98 mg/dL, serum C4 markedly depressed at 6 mg/dL (normal 15-45); serum albumin 3.2 g/dL; positive rheumatoid factor and low-titer ANA. Renal biopsy shows membranoproliferative glomerulonephritis with immune complex deposition positive for immunoglobulin and complement, consistent with cryoglobulin deposition. Which of the following is the most likely diagnosis?