Clinical features of kidney involvement in microscopic microscopic polyangiitis

To evaluate clinical features and outcomes of renal involvement in patients with microscopic polyangiitis (MPA).

We enrolled 99 patients with MPA, diagnosed in accordance with the algorithm of the European Medicines Evaluation Agency (EMEA) and the Chapel Hill consensus conference definition (2012). Serum creatinine (sCr), estimated glomerular filtration rate (eGFR), hematuria and proteinuria were estimated. Frequency of rapidly progressive renal failure (a twofold increase in the sCr level in ≤3 months) was regarded as the clinical equivalent of rapidly progressive glomerulonephritis (RPGN).

Renal involvement was present in 92 (92.9%) patients. RPGN developed in 51 (55,4%) patients. The most common features of kidney involvement were hematuria and subnephrotic proteinuria. Arterial hypertension was revealed in 32 (34.7%) patients and was associated with RPGN (p<0.004). End-stage renal disease (ESRD) developed in 11 (11.9%) patients. Despite effective induction therapy disease relapses occurred in 20 (21.1%) patients during the 1st year, including renal relapses in 12 (13.3%) cases. During 5-year follow up 34 (37.1%) patients developed disease relapses, including renal relapses in 22 (24.4%) patients.

Renal involvement is one of the most common manifestations of MPA with a high frequency of RPGN. More than one third of patients develop disease relapses despite adequate therapy.