Differential Diagnosis (3): Sjögren Syndrome

Abstract

The major renal manifestation of Sjogren syndrome (SjS) is tubulointerstitial nephritis similar to that seen in IgG4-related kidney disease (IgG4-RKD). However, the two diseases can be differentiated by their clinical and histological characteristics. Serum IgG4 is more likely to be elevated and to achieve extremely high concentrations in IgG4-RKD than in SjS. In contrast, SjS patients are far more likely to have anti SS-A (70 %) and anti SS-B (30 %) antibodies than are patients with IgG4-RKD, who are typically seronegative. In the histological aspect, a combination of storiform fibrosis and IgG4 positive plasmacyte infiltration – referred to as a “bird’s eye” pattern – is highly characteristic of IgG4-RKD. On the other hand, tubulitis in SjS is sometimes so severe as to be associated with tubular dysfunction characterized by renal tubular acidosis and hyperkalemia, findings that are unusual in IgG4-RKD. There also appear to be important differences in the pathophysiology of these two conditions, even though there remains much to be learned about the mechanisms of both.