Renal involvement in primary Sjögren's syndrome: natural history and treatment outcome

Overt renal disease in primary Sjögren's syndrome (pSS) manifests as interstitial nephritis and glomerulonephritis. This single centre study aims to describe the natural history and treatment outcome of renal disease in pSS. pSS patients with renal disease were identified, and clinical features, renal biopsy findings, treatment details and renal outcome were recorded. Of the 20 pSS patients with renal disease, 14 had interstitial nephritis (IN), 3 had glomerulonephritis (GN) and 3 had both entities. In the IN group, 3 patients presented with chronic kidney disease (CKD), 4 with renal tubular acidosis (RTA), 2 with symptomatic hypokalaemia, 4 with renal colic and 1 with haematuria/proteinuria. Eight of 14 patients with IN received systemic immunosuppression (IS) during renal disease course and in 6 patients no beneficial effect was observed on renal function, hypokalaemia and RTA. Six of 14 IN patients developed CKD while 5 of them preserved normal renal function during follow-up. In the GN group, 2 patients presented with CKD, 3 with proteinuria/haematuria and 1 with nephrotic proteinuria. GN renal biopsy findings revealed membranoproliferative (MPGN) (n=3), focal segmental glomerulosclerosis (n=1) and fibrillary glomerulopathy (n=1). All 3 MPGN patients had cryoglobulinaemia and in 1 patient cryoglobulinaemic MPGN was clinically diagnosed. All GN patients were treated with immunosuppressive therapy, with stabilisation or improvement of renal function in the 4 cryoglobulinaemia-associated GN patients only. Interstitial nephritis follows a slow course and does not improve with systemic immunosuppression while GN has a favourable treatment response in those with MPGN pathology.