Multiple myeloma presenting as acute tubulointerstitial nephritis

Area of Science:

• Nephrology
• Oncology
• Pathology

Background:

• Acute tubulointerstitial nephritis (ATIN) is a rare paraneoplastic manifestation in multiple myeloma (MM).
• Renal involvement in MM typically presents differently than ATIN.

Observation:

• An 82-year-old male presented with acute kidney injury without typical MM symptoms.
• Renal biopsy revealed light chain-associated ATIN with interstitial inflammation and tubulitis.
• Immunoassays confirmed a significant lambda light chain burden and Bence Jones protein.

Findings:

• Immunofluorescence showed lambda light chain deposition along tubular basement membranes.
• Electron microscopy indicated interstitial edema and inflammation.
• The findings supported a diagnosis of MM presenting as ATIN.

Implications:

• Light chain-associated ATIN should be considered in the differential diagnosis of acute interstitial nephritis.
• Serum free light chains and protein electrophoresis are crucial for diagnosing MM-associated ATIN.
• This case highlights the importance of comprehensive renal workup in suspected paraneoplastic syndromes.