Questions 2 and 3 refer to the following case:
A 58-year-old Caucasian man presents to the emergency department with a 1-week history of hematuria and epistaxis. For the past 3 months he has noticed fatigue and progressive swelling of his legs. Physical examination demonstrates a normotensive male with generalized purpura and ecchymoses, nondistended jugular veins, clear chest to auscultation, regular heart rhythm, mild hepatosplenomegaly, and 3+ pitting edema in both lower extremities extending up to the knees. The stool guaiac test is positive for occult blood. Having read a recent article on amyloidosis, you suspect the diagnosis and order the appropriate workup. The workup demonstrates mild anemia, serum creatinine of 1.3 mg/dL, severe hypoalbuminemia, and elevated lambda free light chains with abnormal kappa-lambda ratio. Protein electrophoresis and immunofixation of serum identifies a small IgG lambda and lambda light chain clonal gammopathy, and 24-hour urine studies demonstrate 6 g of proteinuria, with 85% of urinary protein being albumin. The coagulation profile demonstrates prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT), and mixing studies show immediate correction of both PT and aPTT. You order a fat pad aspiration and biopsy that confirms the presence of amyloidosis.
What is the most likely cause of this patientís bleeding diathesis?