Acute Renal Colic Due to Immunoglobulin Free Light Chain Kidney Stones: A Case Report of an Unusual Complication of Multiple Myeloma.

Kidney failure is common in patients with a monoclonal gammopathy, most frequently due to hypercalcemia or myeloma cast nephropathy. Immunoglobulin crystallization is an uncommon phenomenon that also results in kidney injury. We report the case of a 74-year-old man with recurrent renal colic and acute kidney injury. He presented with κ light chain Bence-Jones proteinuria, hypogammaglobulinemia, anemia, and high plasma κ light chain level, leading to the diagnosis of κ light chain multiple myeloma. One calculus was collected and its analysis revealed a unique protein structure consisting of κ immunoglobulin free light chain. Genetic sequencing of the κ light chain identified a subgroup of variable domain previously identified as prone to crystallization. Eight cycles of cyclophosphamide-bortezomib-dexamethasone chemotherapy resulted in a partial hematologic response and kidney recovery without recurrence of renal colic. This rare case of urinary light chain nephrolithiasis highlights the importance of genetic and molecular analysis of the immunoglobulin variable domain to better understand the wide spectrum of monoclonal gammopathies.