Background The prognostic importance of renal involvement in Systemic Lupus Erythematosus (SLE) is well known. Predominant interstitial nephritis is a rare manifestation of SLE. The prognostic importance of histopathological tubulointerstitial (TIC) changes in renal tissue in patients with lupus nephritis (LN) is very little known.

Objectives Our objectives were to more precisely determine TIC in the renal tissue and correlate these data with clinical features, daily proteinuria and 24-hour creatinine clearance in pts with LN. Our long-term goal is to identify pts during clinical quiescence who may be at high risk of developing progression to renal failure from LN.

Methods Renal biopsies from 26 pts were analysed with emphasis on TIC. At the time of biopsy all pts had defined clinical evidence of active LN. Presence and intensity of oedema, inflammatory mononuclear infiltrate, fibrosis, hyaline casts and tubular atrophy were determined. TIC were graded from 0 to 3 (absent, mild, moderate and severe). We correlated these results with clinical data of 24-hour creatinine clearance (CC) and 24-hour urine total protein excretion (TP) at pre-treatment and post-treatment period.

Results Patients were divided into 4 group: first group with absent TIC (0 score) 6 pts with TP mean 2.17 gr/24 h, CC mean 1.32 ml/s; second group with mild TIC (1–5 score), 12 pts with TP mean 2.61 gr/24 h, CC mean 0.76 ml/s; third group with moderate TIC (6 do 10 score) 5 pts with TP mean 2.67 gr/24 h, CC 0.95 ml/s; forth group with severe TIC (11 to 15 score) 3 pts with TP mean 1.52, CC mean 0.37 ml/s. These analyses we repeated after treatment with corticosteroids and citotoxyc drugs at period of 3 to 6 months and correlated with previous data. Significant results occurred for TP in first group (p < 0.05) and in second group (p < 0.01), as well as in second group for CC (p < 0.05).

Significant improvement for both parameters occurred in group of 12 pts with mild TIC. (TP p < 0.01; CC p < 0.05). In group of pts with severe TIC, TP has decreased as well as CC.

Conclusion TP decrease as well as increase of CC correlated well with mild degree of TIC. TIC could be prognostic predictors in LN. This has to be proved with a greater number of pts.