The occurrence of renal involvement in primary Sjögren's syndrome: a study of 78 patients.

OBJECTIVE: To ascertain the occurrence of renal involvement in patients with primary Sjögren's syndrome (pSS).
METHODS: Urinary total protein excretion from 24 h urine collection, as well as urinary excretion rates of albumin, alpha-1 microglobulin (alpha1m) and IgG from overnight 8 h collections, were determined from 78 pSS patients (75 females, three males). Urine acidification capacity after oral ammonium chloride load was tested in 55 of these patients.
RESULTS: Mild proteinuria (0.15-0.42 g/24 h) was observed in 34 patients (44%). Increased urinary excretion rates of albumin (>/=20 microgram/min), alpha1m (>/=7.0 microgram/min) or IgG (>/=5.0 microgram/min) were detected in nine (12%), nine (12%) and 11 patients (14%), respectively. Latent or overt distal renal tubular acidosis (dRTA) was observed in 18 out of 55 patients with pSS (33%). These patients had a longer duration of the disease (10+/-4 vs 8+/-4 yr; P</=0.05); they also had proteinuria (67 vs 27%; P</=0.025) and hypertension (44 vs 14%; P</=0.05) more frequently, and significantly higher serum creatinine (92+/-39 vs 78+/-13 micromol/l; P</=0.025) and serum beta-2 microglobulin (beta2m) levels (3.3+/-1.6 g/l vs 2.6+/-0. 6 g/l; P</=0.025) as compared to patients with normal urine acidification capacity.
CONCLUSIONS: Inadequate renal acidification capacity, as well as mild proteinuria, were frequently found in patients with pSS. Those with dRTA had longer disease duration, a higher level of serum beta2m, and they had proteinuria and hypertension more frequently than those with normal renal acidification capacity.