Clinical and pathological characterization of patients with microscopic polyangiitis with medium artery involvement.

Objective: To study the clinical and pathological characteristics of patients with microscopic polyangiitis (MPA) with medium artery involvement.

Methods: Hospitalized patients with MPA in recent two years were retrospectively studied. Their clinical and pathological features were compared between patients with and without renal medium artery involvement.

Results: Thirty-nine patients had renal pathology confirmed MPA. Nine cases were with medium artery involvement. For the 30 patients without medium artery involvement, 24/30 had crescentic glomerulonephritis and 11/30 also had focal segmental glomerular fibrinoid necrosis; clinically, 21/30 patients were pANCA/MPO-ANCA positive, 26/30 had acute renal failure with an average duration of 14 weeks before MPA was diagnosed, eight cases achieved complete remission after intensive immunosuppressive therapy. Nine MPA patients had medium artery involvement, manifested as segmental fibrinoid necrosis of major branch of arcuate artery, glomerulus ischemia was predominant, but crescentic lesions were mild, none of them reached crescentic glomerulonephritis. Five of the nine were pANCA/MPO-ANCA positive, eight out of the nine patients had acute renal failure with an average duration of eight weeks before diagnosed, seven of the nine achieved complete remission after intensive immunosuppressive therapy. In comparison, MPA with medium artery involvement had a shorter duration (p < 0.05), less crescentic glomerulonephritis in patients with acute renal failure (p < 0.01) and more patients achieved complete remission after treatment (p < 0.05).

Conclusion: In present study, about 23% MPA patients had medium artery involvement and their impaired renal function is mainly due to extensive glomerular ischemia. These patients progressed to acute renal failure quicker and responded to therapy better.