A Case of AL Amyloidosis: A Common Cause of Nephrotic Syndrome without the Damage

Introduction: AL amyloidosis, the most common subtype of systemic amyloidosis, is characterized by the overproliferation of immunoglobulin-associated proteins by plasma cells. These unstable proteins misfold into amyloid fibrils and deposit into various tissues. Approximately two-thirds of patients will develop nephrotic syndrome from amyloid deposition in the glomeruli, leading to progressive renal dysfunction and failure. We present a unique case of AL amyloidosis with nephrotic syndrome in the absence of renal impairment. Case Description: A 79-year old male, with a history of dyslipidemia and paroxysmal atrial fibrillation, presents for worsening edema and dyspnea on exertion non-responsive to loop diuretics. On outpatient echocardiogram, he had new aortic regurgitation, pleural effusion, and spot urinalysis with albuminuria 3000mg. Metabolic panel showed BUN 20, creatinine 1.0, and eGFR 77. Urine studies revealed a protein/creatinine ratio 13.6. An echocardiogram revealed left ventricular hypertrophy with speckling suspicious for amyloidosis infiltration. A renal ultrasound showed a simple cyst but otherwise unremarkable. His renal biopsy was Congo red positive AL amyloidosis associated with lambda-light changes and acute tubular injury. A bone marrow biopsy confirmed increased abnormal plasma cells and amyloid deposition within vessels. He was discharged home with diuretics and angiotensin-converting enzyme inhibitors for his nephrotic syndrome and plans to enroll in a clinical trial for his AL amyloidosis. Discussion: The kidney glomeruli are the most frequent site of AL amyloid accumulation, leading to proteinuria. Notably, >5g/day and reduced eGFR <50 are closely associated with the development of end-stage renal disease. Existing criteria measure the severity of the nephrotic syndrome with progression to ESRD as an inverse correlation of proteinuria to eGFR. In this patient, his protein/creatinine ratio can be approximated as proteinuria around 13.6g/day but with a normal eGFR. There is no evidence of that relationship, nor did his acute tubular injury seen on the renal biopsy manifest on labs. While an unusual case without renal damage, it solidifies the use of proteinuria not only for the detection of AL amyloidosis and its organ involvement but also reaffirms the ongoing significance as a biomarker of damage or response to therapy further down the line.