Systemic AL Amyloidosis With an Undetectable Plasma Cell Dyscrasia: A Rare Entity

ABSTRACT

Introduction: AL Amyloidosis is characterized by a plasma cell dyscrasia that can be detected in 99% by monoclonal protein on abnormal serum free light chain (sFLC) concentrations or immunofixation electrophoresis (IFE). Case Description A 47-year-old man was admitted to the emergency department and afterward to the intensive care unit due to severe COVID-19-associated pneumonia. Initial laboratory studies showed hemoglobin 12.1 g/dL, creatinine 2 mg/dL, albumin 1.69 g/ dL, AST 20 U/L, ALT 19 UI, urine analysis with no erythrocytes, urine protein/creatinine ratio 4.9 g/g, HbA1c 5.5%, C3 150 mg/dL, C4 35 mg/dL. Serological testing for hepatitis B, C, HIV, ANA, and anti-PLA2R were negative. After three months of hospitalization, the patient was discharged home and lost his outpatient follow-up. He returned five months later with a nephrotic syndrome. Laboratory studies showed creatinine 1.47 mg/dL, urine proteins 5.7g/day, sFLC lambda 90.1 mg/L (8.3-27), sFLC kappa 43 mg/L (6.7-22.4), sFLC ratio 0.48 (0.31-1.56), urine and serum protein electrophoresis negative, urine and serum IFE negative. We performed a renal biopsy, consistent with amyloidosis with positivity for Congo red staining. Immunofluorescence reported light chain restriction +++ for lambda (figure 1) and was negative for IgG, IgM, IgA, C1q, C3c, kappa, and albumin. A bone biopsy reported no evidence of plasmatic cell neoplasia and was negative for Congo red staining. An echocardiogram showed no evidence of amyloid affection. Hematology stratified the patient as low risk, so they started protocol for autologous stem cell transplantation as definitive treatment but decided to consider CyBorD as induction therapy. Discussion(s) This case illustrates a patient with systemic AL amyloidosis without evidence of plasma cell dyscrasia by conventional techniques. It could be explained because the hematologic disease is so subtle that it goes undetected. The parameter for response in his follow-up will be the improvement of proteinuria, as we cannot measure classic criteria of hematologic response. Figure 1.