Two cases of reversible Fanconi syndrome induced by lenalidomide

Kidney disease in multiple myeloma

Renal disease is a frequent complication of symptomatic multiple myeloma, that increases morbidity and reduces quality of life and overall survival. It may result from various lesions, the most frequent being light chain cast nephropathy (LCCN), related to precipitation of monoclonal free light chains (FLC) with uromodulin in distal tubules. Rapid identification of the type of kidney disease with appropriate management is key. LCCN typically reveals the underlying myeloma and manifests with severe acute kidney injury, high serum FLC level (>500 mg/l) and predominant light chain proteinuria (urine albumin/creatinine ratio <10 %). Urgent therapy is required, based on vigorous fluid expansion, correction of precipitating factors and introduction of efficient anti-myeloma therapy which choice should consider renal elimination of each agent and patient frailty. Early and deep reduction in serum FLC level conditions renal recovery, warranting assessment of efficacy by serial serum FLC level monitoring. In newly diagnosed patients, the combination of bortezomib, high-dose dexamethasone and an anti-CD38 monoclonal antibody is commonly used. The benefit to risk balance of quadruplets incorporating cyclophosphamide or an immunodulatory agent requires to be evaluated in prospective studies. In patients with severe acute kidney injury, reinforcing chemotherapy with FLC removal through plasma exchange or high-cutoff hemodialysis may increase the probability of renal response, despite controversial data from randomized trials. Histological assessment of the extent of cast formation and interstitial fibrosis/tubular atrophy may help evaluating renal prognosis and refining therapy. Thanks to improved overall survival, renal transplantation may be considered in selected candidates with end-stage kidney disease.

Pathological characteristics of light chain crystalline podocytopathy

Monoclonal immunoglobulin light chain (LC) crystalline inclusions within podocytes are rare, poorly characterized entities. To provide more insight, we now present the first clinicopathologic series of LC crystalline podocytopathy (LCCP) encompassing 25 patients (68% male, median age 56 years). Most (80%) patients presented with proteinuria and chronic kidney disease, with nephrotic syndrome in 28%. Crystalline keratopathy and Fanconi syndrome were present in 22% and 10%, respectively. The hematologic condition was monoclonal gammopathy of renal significance (MGRS) in 55% and multiple myeloma in 45%. The serum monoclonal immunoglobulin was IgG κappa in 86%. Histologically, 60% exhibited focal segmental glomerulosclerosis (FSGS), often collapsing. Ultrastructurally, podocyte LC crystals were numerous with variable effacement of foot processes. Crystals were also present in proximal tubular cells as light chain proximal tubulopathy (LCPT) in 80% and in interstitial histiocytes in 36%. Significantly, frozen-section immunofluorescence failed to reveal the LC composition of crystals in 88%, requiring paraffin-immunofluorescence or immunohistochemistry, with identification of kappa LC in 87%. The LC variable region gene segment, determined by mass spectrometry of glomeruli or bone marrow plasma cell sequencing, was IGKV1-33 in four and IGKV3-20 in one. Among 21 patients who received anti-plasma cell-directed chemotherapy, 50% achieved a kidney response, which depended on a deep hematologic response. After a median follow-up of 36 months, 26% progressed to kidney failure and 17% died. The mean kidney failure-free survival was 57.6 months and was worse in those with FSGS. In sum, LCCP is rare, mostly associates with IgG κappa MGRS, and frequently has concurrent LCPT, although Fanconi syndrome is uncommon. Paraffin-immunofluorescence and electron microscopy are essential to prevent misdiagnosis as primary FSGS since kidney survival depends on early diagnosis and subsequent clone-directed therapy.

Management of acute kidney injury in symptomatic multiple myeloma

Symptomatic multiple myeloma is commonly complicated by acute kidney injury through various mechanisms. The most frequent is the precipitation of monoclonal free light chains with uromodulin in the distal tubules, defining light chain cast nephropathy. Early diagnosis and identification of the cause of acute kidney injury are required for optimizing management and avoiding chronic kidney injury that strongly affects quality of life and patient survival. In light chain cast nephropathy, often manifesting with severe acute kidney injury, renal recovery requires urgent intervention based on vigorous rehydration, correction of precipitating factors, and efficient anti-plasma cell chemotherapy to rapidly reduce the secretion of nephrotoxic free light chains. Currently, the association of the proteasome inhibitor bortezomib with high-dose dexamethasone is the standard regimen in newly diagnosed patients. The addition of another drug such as cyclophosphamide or an immunodulatory agent may improve free light chain response but raises tolerance concerns in frail patients. Further studies are warranted to confirm the role of anti-CD38 monoclonal antibodies, whose efficacy and tolerance have been documented in patients without renal impairment. Despite controversial results from randomized studies, recent data suggest that in patients with light chain cast nephropathy and acute kidney injury requiring dialysis, the combination of chemotherapy with free light chain removal through high-cutoff hemodialysis may increase renal response recovery rates. Kidney biopsy may be helpful in guiding management and assessing renal prognosis that appears to depend on the extent of cast formation and interstitial fibrosis/tubular atrophy. Because of continuous improvement in life expectancy of patients with multiple myeloma, renal transplantation is likely to be increasingly considered in selected candidates.