RESUMO
BACKGROUND AND OBJECTIVE: Lupus nephritis (LN) is a major complication in patients with systemic lupus erythematosus (SLE). Tubulointerstitial injury is an inflammatory process that, if not attenuated, can promote renal damage. Despite this, the current 2003 ISN/RPS "glomerulocentric" classification does not include a score for tubulointerstitial injury. We sought to establish predictors for tubulointerstitial injury and to determine their influence on renal outcomes. METHODS: This is a retrospective study of a cohort of 166 patients with biopsy-proven LN diagnosed in a Spanish referral center, with a median follow-up of 86 months. Chronic tubulointerstitial lesions were defined as interstitial fibrosis and tubular atrophy (IF/TA), whereas tubulointerstitial inflammation (TII) was defined as an acute interstitial lesion. Activity (0-24) and chronicity (0-12) indices were assigned. OUTCOME: Composite outcome, defined as advanced CKD or development of kidney failure. RESULTS: The prevalence of tubulointerstitial lesions was 69.3%. Eighty-one of the biopsies had features of tubulointerstitial inflammation and only 6 of these 81 (7%) patients had moderate/severe tubulointerstitial inflammation. The incidence of interstitial fibrosis and tubular atrophy was 56.6%. Renal survival was shorter in patients with moderate/severe as compared with absent/mild interstitial fibrosis and tubular atrophy (median: 15-19 years, p = 0.009). In the Cox regression model, the grade of interstitial fibrosis and tubular atrophy was independently associated with shorter renal survival (hazard ratio: 3.9, 95% CI 1.4-10.5; p = 0.008) after adjusting for degree of IF/TA and hypertension or diabetes. CONCLUSIONS: The extent of tubulointerstitial inflammation emerged as an independent predictor of renal survival after adjusting for the grade of interstitial fibrosis and tubular atrophy and co-morbid conditions including hypertension or diabetes. Regarding disease duration at the time of renal biopsy, no significant association was found between the interstitial fibrosis and tubular atrophy groups. The results reported herein need to be validated in future studies to include also groups of patients who usually have a worse prognosis. Consensus on histological classification is needed to aid in defining prognosis.