Renal involvement in primary Sjogren's syndrome: a prospective cohort study

The objective of the study is to prospectively evaluate the spectrum of clinical and subclinical renal involvement in patients with primary Sjogren's syndrome (pSS). Of the 174 patients screened, seventy patients with pSS underwent renal function tests, urine examination, renal ultrasound, arterial blood gases, urine pH followed by urine acidification test and renal biopsy (if indicated). Renal tubular acidosis (RTA) was treated with alkali replacement and moderate-severe tubulointerstitial nephritis (TIN) was treated with oral prednisolone. Sixty-two patients completed 1-year follow-up. A comparison was made between patients with and without renal involvement. Thirty-five (50%) patients had renal involvement. They had a lower baseline eGFR (71.85 +/- 18.04 vs. 83.8 +/- 17, p=0.005). Twenty-nine patients had RTA (25 complete and 4 incomplete). Eleven patients had urinary abnormalities. Patients with RTA (n=29) were younger (34.9 +/- 9 vs. 42 +/- 11.3, p=0.006), had fewer articular (34% vs. 78%, p=0.001) and ocular sicca (62% vs. 88%, P=0.01) than those without RTA (n=41) and commonly presented with hypokalemic paralysis. On biopsy, TIN (9/17) and IgA nephropathy (3/17) were most common. On follow-up, there was no clinically significant change in eGFR; however, one patient with renal calculi and incomplete distal renal tubular acidosis (dRTA) progressed to complete dRTA. Two patients treated with steroids had marginal improvement in eGFR. Renal involvement in pSS is under-recognized with the most common manifestation being RTA presenting with hypokalemic paralysis. These patients are younger with less articular and sicca symptoms. Subclinical RTA may progress to complete RTA. Renal biopsy should be considered in all patients with renal involvement.