Follow-up of steroid-resistant nephrotic syndrome: tubular proteinuria and enzymuria

PATRICIA G. VALLES; MIRTA PERALTA; LILIANA CARRIZO; LAURA MARTÍN; ILIANA PRINCIPI; ADRIANA GONZALEZ; WALTER MANUCHA

PEDIATRIC NEPHROLOGY

Springer International

Lugar: Berlín; Año: 2000 vol. 15 p. 252 - 258

0931-041X

The aim of this study was to examine the compromise of proximal tubule cells in steroid-resistant nephrotic syndrome patients with a histologic diagnosis of focal segmental glomerulosclerosis (FSGS) through assessment of the urinary levels of B2-microglobulin (B2M) and N-acetyl-B-D-glocosaminidase (NAG) during active disease and remission over a follow-up period of 3 year. We studied 34 children with nephrotic syndrome: 12 with steroid-resistant nephrotic syndrome (SRNS) and massive proteinuria, 7 with steroid-dependent nephrotic syndrome (SDNS) and 15 with steroid-sensitive nephrotic syndrome (SSNS). Of the SSNS patients, 8 children were in remission (RM) and 7 were in relapse (RL). Seven heathy children were included as controls. Urinary B2M, measure by enzyme-linked immunosorbent assay, was significantly increased in the SRNS group as compared to the SDNS group (p<0.01), SSNS in remission (p<0.01), and controls (p<0.01). There were no differences between the SRNS group and SSNS in relapse. Analysis of urinary N-acetyl-B-D-glucosaminidase (U-NAG) by colorimetric assay showed significantly higher values in the SRNS group of patients than in SDNS, SSNS, and control group. A positive correlation between U-NAG and proteinuria was demonstrated (r=0.73, p<0.01). The SRNS group of patients (n=12, 11 with a histologic diagnosis od FSGS and one with diffuse mesangial proliferation) was treated with the same protocol of i.v. methylprednisone and oral cyclophosphamide. Log-term follow-up showed a progressive decrease in U-B2M and U-NAG excretion to control values in the 3rd year, except in one patient who did not respond to the treatment. In the FSGS patient, evaluation of the contribution of structural interstitial histological abnormalities, including each of the histological parameters considered in interstitial scarring to the functional tubule abnormalities assessed by B2M and NAG excretion, was performed by multiple regression analysis. The r values for B2M and NAG were 53.99%, p=0.19, and 57,90%, p=0.14, respectively; neither was significant. We conclude that: (1) proximal tubule cell dysfubction, partially affected by massive albuminuria, may account for the higher values of B2M and NAG excretion in the SRNS patients and (2) urine B2M and NAG levels are not helpful in identifying histological evidence of structural tubulointerstitial damage in children with steroid-resistant nephrotic syndrome.