MO114: Incidence and Spectrum of Biopsy-Proven Dysproteinemic Kidney Diseases: A Single-Centre Experience

Abstract BACKGROUND AND AIMS We aimed to evaluate the incidence and clinical features of patients with biopsy-proven dysproteinemic kidney diseases (group 1), as well as spectrum of biopsy-proven kidney diseases of patients with monoclonal gammopathy (MG) or abnormal free light chain (FLC) ratio (group 2) at our institution. METHOD This was a single-centre retrospective study of all patients who had native kidney biopsies at the Singapore General Hospital between October 2015 and December 2021. Demographic, clinical, laboratory and histological data were retrieved from electronic medical records to identify patients with biopsy-proven dysproteinemic kidney diseases (group 1) and patients with positive MG and/or abnormal FLC (κ to λ) ratio who underwent kidney biopsy (group 2). Patients were considered to have MG if they tested positive on any of the following tests: serum protein electrophoresis, serum immunofixation, urine protein electrophoresis or urine immunofixation. Abnormal FLC ratio is defined as a ratio outside the range of 0.27–1.65 in patients with eGFR ≥60 mL/min/m2 or 0.37–3.10 in patients with eGFR <60 mL/min/m2. RESULTS Out of 1066 patients who underwent kidney biopsy between October 2015 and December 2021, 25 (2.3%) patients were diagnosed with dysproteinemic kidney diseases (group 1). The median age of the patients at diagnosis was 65.6 years (IQR 58.6, 68.2), and majority was male (17/25; 68.0%). Haematological diagnoses present in this cohort include multiple myeloma (5/25; 20.0%), chronic lymphocytic leukaemia (2/25; 8.0%), Waldenstrom's macroglobulinaemia (2/25; 8.0%) and mantle cell lymphoma (1/25; 4.0%). Two-thirds of the patients had acute kidney injury (AKI) at time of biopsy (17/25; 68.0%). All patients presented with proteinuria, and nephrotic syndrome was noted in approximately half of the patients (15/25; 60.0%). Hypocomplementemia was present in a third (7/21; 33.3%) of the patients who had complement levels performed prior to biopsy, with low C3 and low C3/C4 observed in 5 and 2 patients, respectively. The most common histological lesion is immunoglobulin-related amyloidosis (8/25; 32.0%), followed by proliferative glomerulonephritis with monoclonal immune deposits (PGNMID) (6/25; 24.0%) and light-chain cast nephropathy (4/25; 16.0%). Sixteen (64%) patients fulfilled criteria for monoclonal gammopathy of renal significance (MGRS). All patients with PGNMID had undetectable MG and normal FLC ratio at diagnosis. Among these 1066 patients who underwent kidney biopsy, 396 patients had serum/urine electrophoresis, serum/urine immunofixation and/or FLC performed prior to biopsy. A total of 44 (11.1%) patients with detectable MG and/or abnormal FLC ratio were identified (group 2), 5 of whom had previously known haematological conditions. Dysproteinemic kidney diseases were diagnosed in 14 (31.8%) patients. Amongst patients with non-dysproteinemic diagnosis, diabetic/hypertensive nephropathy was the most frequent (15/30; 50.0%). Majority of the remaining patients had a variety of glomerulonephritides and renal vasculitides (10/30; 33.3%), or tubulointerstitial diseases (2/30; 6.7%). In univariate analysis, non-diabetic status (P < .001), presence of AKI (P = .032) and abnormal FLC ratio (P = .005) increased the likelihood of diagnosing dysproteinemic kidney disease in this group of patients. CONCLUSION AKI and proteinuria are common in dysproteinemia kidney diseases. Non-diabetic status, presence of AKI and abnormal FLC ratio increased the likelihood of diagnosing dysproteinemic kidney disease.