Tubulointerstitial lesions in lupus nephritis: International multicentre study in a large cohort of patients with repeat biopsy

Background The glomerulocentric International Society of Nephrology/Renal Pathology Society (ISN/RPS) classification is the gold standard for the evaluation of lupus nephritis, while tubulointerstitial (TIN) parameters are often under-recognized in pathological reports. Methods Renal biopsies from 142 patients who underwent repeat biopsy (RB) were evaluated for the following histological parameters: (i) inflammatory interstitial infiltrates; (ii) interstitial fibrosis; (iii) tubulitis; and (iv) tubular atrophy. The inter-relationships between the four TIN variables were explored by multivariate analysis. A linear mixed model was used to investigate the potential impact of TIN variables on EGFR and proteinuria at the two biopsy occasions. Results The study showed that moderate-severe lesions were not so frequent at the reference biopsy, but more extensively represented upon RB. A strong association was found between the two inflammatory indices and between those related to chronic damage, while the relationship with the ISN/RPS classification was present at RB. If class IV-G was the most related with TIN (especially at RB), the existence of primary TIN in class II patients was also confirmed. Finally, our results support the hypothesis that tubulitis is an independent predictive factor for EGFR. Conclusions We recommend that the standard histological evaluation of SLE nephritis also includes TIN features.