A 64-year-old man with past medical history of pre-diabetes, hypertension, benign prostate hyperplasia (BPH), elevated PSA, gastroesophageal reflux disease (GERD), and degenerative joint disease affecting T11 to L1 after extensive back surgery 1 year previously presented with diffuse joint and bone pain the past few months as well as fatigue. He had a rising serum creatinine level and was referred to nephrology. His serum creatinine level was 1.1 mg/dL 1 year ago, 2.2 mg/dL 1 month ago, and 3.9 mg/dL at the current visit. He noticed foamy urine, but denied flank pain, dysuria or hematuria. Medications included amlodipine, famotidine, finasteride and tamsulosin. The physical examination was notable for trace edema in the lower extremities, but is otherwise unremarkable. Laboratory test values showed:
Serum sodium 136 mmol/L, potassium 4.7 mmol/L, chloride 104 mmol/L, bicarbonate 19 mmol/L, BUN 60 mg/dL, creatinine 3.9 mg/dL, calcium 10.5 mg/dL; white blood cell count 10.5×103/MCL, hemoglobin 9.9 g/dL, platelet count 360×103/MCL. Urinalysis was positive for blood and negative for protein. His 24-hour urine protein was 4.5 grams. All serology including ANA, ANCA, hepatitis B, hepatitis C, HIV, and syphilis were negative. Complement C3 and C4 are normal. Serum protein immunofixation detected a monoclonal spike in the IgA lambda regional. Serum lambda light chain is 5250 mg/L and kappa light chain is 3.4 mg/L. Urine sediment revealed muddy brown granular cell casts consistent with acute tubular necrosis (ATN).
A renal biopsy showed lambda light chain cast nephropathy with ATN and interstitial inflammation.