Large variability of the activity and chronicity indexes within and between histological classes of lupus nephritis

Systemic lupus erythematosus (SLE) is characterized by a multifaceted pathogenesis and a heterogeneous clinical expression. The kidney involvement is almost unavoidable in all forms of SLE with chronic evolution, 75% of patients developing renal lesions defined as lupus nephritis (LN) - a glomerulonephritis with an extremely diverse lesion spectrum. The present study aimed to reevaluate a series of cases diagnosed as LN, focusing on the histological features in correlation with the level of activity and chronicity. The study group comprised 46 patients. The specimens obtained through percutaneous needle biopsies were processed for light microscopy and immunofluorescence exams. The reevaluation process focused on the major morphological parameters ensuring: (i) a detailed description of the lesions, (ii) the class diagnosis in accordance with the International Society of Nephrology÷Renal Pathology Society (ISN÷RPS) classification, (iii) the activity and chronicity indexes. In 39 out of the total of 46 (84.78%) cases, the class of LN established at the time of the renal biopsy was confirmed in the reevaluation process. The differences in diagnosis were present in seven cases, initially considered as pure membranous glomerulonephritis - class V. The values of indexes indicated a great variability of LN within the same class. The interobserver agreement for the scoring of activity and chronicity indexes was 0.8 and 0.95, respectively. Our study emphasizes the complex lesion character, which requires an individual and accurate identification, followed by integration in the classification algorithm used to define the classes and subclasses of LN diagnosis. The degree of activity and chronicity in SLE must be refined through a much more precise correspondence between the score value and the limitation or extension of corpuscular and interstitial lesions.