A 30-year-old female patient presents with low-grade fever, weight loss, and polyarthralgia over the past 3 months. Physical examination reveals mild pitting edema in both lower limbs. Urinalysis (UA) shows urinary protein (++), and 10-20 red blood cells (RBC)/HP. p-ANCA is positive, while other autoantibodies are negative. Renal biopsy pathology demonstrates necrotizing inflammatory changes in small arteries without immune complex deposition. Renal angiography shows no vascular stenosis. The most likely diagnosis is: