Renal disease in primary Sjögren's syndrome

Sammanfattning: Primary Sjögren's syndrome (SS) is characterised by inflammation in the lacrimal and salivary glands. The kidneys may be involved, e.g. tubulointerstitial nephritis (TIN) and distal renal tubular acidosis (dRTA). dRTA is often associated with hypocitraturia, and both represent risk factors for the development of urolithiasis. The present investigations were undertaken to evaluate renal tubular function (including -dRTA), glomerular filtration rate (GFR), renal histopathology and mechanisms of stone formation, as well as the serum IgG subclass pattern in patients with SS. Furthermore, patients presenting with urolithiasis and dRTA in absence of sicca symptoms, as well as patients with urolithiasis andhypocitraturia, were studied with respect to autoantibodies and clinical features of SS.Renal tubular dysfunction, such as dRTA; impaired urine concentrating ability; hypocitraturia; and decreased tubular reabsorption of phosphate (1RP%), was conunonly detected in the SS-patients. Tubular proteinuria (al-microglobulin) and tubular enzymuria (NAG) were primarily associated with decreased GFR.GFR, investigated with 5Icr-EDTA plasma clearance, was below the reference limit in 33% of SS-patients. An inverse correlation was found between GFR and the extent of tubulointerstitial nephritis (adjusted CTIN score). Decreased GFR was mostly due to TIN, although urolithiasis and upper urinary tract infections may have contributed in some patients.TIN was demonstrated in most biopsied patients with SS, and the histopathological picture was characterised by mainly focal interstitial inflanunation, tubular atrophy, interstitial fibrosis and a varying extent of glomerular sclerosis.Fourty-one percent of the SS-patients had formed at least one stone, and calcium phosphate was the main constituent in most stones. All stone formers had dRTA, and most of them had hypocitraturia. Urinary calcium and urate excretion was also significantly higher than in non-stone formers.The SS-patients often had low serum levels of IgG2, despite high levels of total IgG. Low levels of IgG2 were sometimes associated with infections. A high IgG lngG2 ratio indicated autoimmune disease.Of 10 patients presenting with urolithiasis and dRTA, anti-SS-A antibodies were detected in eight. Subjective sicca symptoms subsequently developed l-48 years after the presentation of urolithiasis, and objective signs of SS were found in 7 patients.In a large population of hypocitraturic stone formers, ANA and anti-SS-A antibodies were commonly detected in the women but not in the men. Four of 14 evaluated hypocitraturic women with anti-SS-A antibodies or ANA, fulfilled the criteria for SS.In conclusion, the present investigations show that 24-hour urinary excretion of citrate is a valuable tool for detection of renal disease in SS, slightly-moderately decreased GFR is not unusual in SS-patients with. renal disease, the "adjusted CTIN score" can be a useful tool for quantifying the extent of tu'bulointerstitial nephritis, and the urine composition in stone formers with SS is similar to that of other dRT A-patients.The possibility of a Sjögren-related renal disease charcterised by urolithiasis and/or dRTA and antibodies to SS-A, regardless of whether subjective sicca symptoms are present or not, is hypothesised.