Bence Jones proteinuria is found on a urinalysis specimen from a 63 year old woman. She is developing chronic renal failure and has a high serum urea nitrogen and creatinine. A radiograph of the veebral column demonstrates multiple 1 to 2 cm rounded areas of decreased bone density. The pathological examination from a renal biopsy is likely to show which of the following complication?

**Core Concept**
Bence Jones proteinuria is a characteristic finding in multiple myeloma, a type of plasma cell dyscrasia. This condition is associated with the production of abnormal immunoglobulins, which can lead to various systemic complications, including renal impairment and bone lesions.

**Why the Correct Answer is Right**
The presence of Bence Jones proteins (light chains of immunoglobulins) in the urine is a hallmark of multiple myeloma. These light chains can accumulate in the kidneys, leading to cast formation and renal damage. In this case, the patient's renal failure, as indicated by high serum urea nitrogen and creatinine levels, is likely due to the effects of multiple myeloma on the kidneys. The bone lesions observed on the radiograph are also consistent with multiple myeloma, which can cause lytic bone lesions due to the proliferation of malignant plasma cells.

**Why Each Wrong Option is Incorrect**
* **Option A:** While amyloidosis can also cause renal failure and proteinuria, it is not directly associated with Bence Jones proteinuria or the characteristic bone lesions of multiple myeloma.
* **Option B:** Focal segmental glomerulosclerosis (FSGS) is a cause of nephrotic syndrome and renal failure, but it is not typically associated with Bence Jones proteinuria or the bone lesions of multiple myeloma.
* **Option C:** Chronic pyelonephritis can cause renal failure and proteinuria, but it is not typically associated with Bence Jones proteinuria or the characteristic bone lesions of multiple myeloma.

**Clinical Pearl / High-Yield Fact**
Multiple myeloma should be considered in the differential diagnosis of patients with unexplained renal failure, bone pain, or proteinuria, especially in the context of a characteristic radiographic appearance of "punched-out" lytic bone lesions.

**Correct Answer:** D.

✓ Correct Answer: D. Amyloidosis