A case of immunofluorescence-negative light chain deposition disease diagnosed by mass spectrometry.
Mayu Iwata, Mineaki Kitamura, Tomohisa Tsuyuki et al.
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Case in brief
A 53-year-old man with kidney dysfunction and edema had nodular glomerular lesions on biopsy, but immunofluorescence did not show immunoglobulin or light-chain deposits. Serum and urine testing detected κ-type Bence Jones protein, and bone marrow examination diagnosed multiple myeloma. Electron microscopy showed powdery deposits along glomerular and tubular basement membranes, although further tissue staining also failed to demonstrate light chains. Laser microdissection with liquid chromatography–tandem mass spectrometry identified κ light chain in the deposits, establishing light chain deposition disease and linking the renal lesion to the plasma cell disorder. After plasma cell-directed therapy, kidney function improved and dialysis was avoided.
What made this case unusual
Despite suggestive electron-microscopic findings and a concurrent plasma cell disorder, light-chain deposition was undetectable by conventional and additional immunostaining; mass spectrometry established the renal diagnosis.
Diagnostic / clinical pearl
When biopsy morphology and clinical findings suggest monoclonal light-chain deposition disease but tissue immunostaining is negative, mass spectrometry of microdissected deposits can help establish their composition.