Amyloid casts within renal tubules: a singular finding in myelomatosis

Two kinds of rare light chain cast nephropathy caused by multiple myeloma: case reports and literature review

BACKGROUND

Light chain cast nephropathy (LCCN) is the most common renal disease caused by multiple myeloma (MM). In addition to ordinary light chain protein casts, there are a few rare casts with unique shapes, including light chain amyloid casts (LCAC) and light chain crystal casts (LCCC).

CASE PRESENTATIONS

Here, we report two patients. Patient 1 is a 72-year-old man who was clinically diagnosed with MM and acute kidney injury (AKI). Pathological examination of a renal biopsy revealed that there were many amyloid casts in the distal tubules that had a lightly-stained central area and a deeply-stained burr-like edge. The marginal zone of the cast was positive for Congo red staining and contained numerous amyloid fibers, as observed by electron microscopy. No systemic amyloidosis was found. The patient received 4 courses of bortezomib-based chemotherapy, and then, his MM achieved partial remission. Patient 2 is a 57-year-old man who was also clinically diagnosed with MM and AKI. Pathological examination of a renal biopsy showed that there were many crystalline casts in the distal tubules that were fully or partially composed of crystals with different shapes, including rhomboid, needle, triangle, rectangle and other geometric shapes. Congo red staining was negative. Crystals were also detected in the urine of this patient. After 9 courses of treatment with a bortezomib-based regimen, his MM obtained complete remission and his renal function returned to normal.

CONCLUSIONS

LCAC and LCCC nephropathy caused by MM are two rare types of LCCN, and both have their own unique morphological manifestations. LCAC nephropathy may not be accompanied by systemic amyloidosis. The diagnosis of these two unique LCCNs must rely on renal biopsy pathology, and the discovery of urine crystals is of great significance for indicating LCCC nephropathy.

Myeloma cast nephropathy with diffuse amyloid casts without systemic amyloidosis: two cases report

Background

Multiple myeloma (MM) is a plasma-cell derived hematologic malignant disease. The malignant proliferating plasma cells secrete massive monoclonal immunoglobulins which lead to various pathologic types of renal injury. Myeloma cast nephropathy (MCN) is the most common histopathologic lesion with the worst renal prognosis. Rarely, the free light chains in the protein casts can form amyloid fibrils. Here, we reported two rare cases of MCN with diffuse amyloid casts.

Case presentation

Case 1: A 54-year-old Chinese man presented with a 4-year history of multiple myeloma, proteinuria and hematuria. He had monoclonal IgAλ plus free λ spike in both serum and urine. He had been on chemotherapy for 4 years and maintained normal serum creatinine until 11 months ago. Then, his renal function deteriorated and he went on hemodialysis 4 months before admission. Renal biopsy showed diffuse amyloid casts in the tubular lumens, without any obvious amyloid deposits in other kidney compartments or signs of extra-renal amyloidosis. The amyloid fibrils formed around mononuclear cells which were CD68 negative. According to the morphology and location, these mononuclear cells were considered as tubular epithelial cells. The patient was maintained on chemotherapy and hemodialysis. He died 8 months after renal biopsy.

Case 2: A 58-year-old Chinese man presented with a one-and-a-half-year history of proteinuria and slowly rising serum creatinine. He had monoclonal IgDλ spike in both serum and urine. Amyloid casts were observed in the tubular lumens and mononuclear cells could be identified in the center of some casts. There were no amyloid deposits in other kidney compartments and no sign of systemic amyloidosis. The patient also had fine granular deposits along the tubular basement membrane with λ linear staining along tubular basement membrane suggesting light chain deposition disease. He was treated with bortezomib-based chemotherapy followed by lenalidomide-based chemotherapy and achieved very good partial remission (VGPR). After 27 months of follow-up, the patient still showed no signs of systemic amyloidosis.

Conclusions

These 2 cases of MCN with diffuse amyloid casts have different histopathologic characteristics from the usual myeloma casts and tubular epithelial cells might play important roles in the pathogenesis.

Intratubular amyloid in light chain cast nephropathy is a risk factor for systemic light chain amyloidosis

Light chain cast nephropathy is the most common form of kidney disease in patients with multiple myeloma. Light chain casts may occasionally show amyloid staining properties, that is, green birefringence after Congo red staining. The frequency and clinical significance of this intratubular amyloid are poorly understood. Here, we retrospectively assessed the clinicopathological features of 60 patients with histologically proven light chain cast nephropathy with a specific emphasis on intratubular amyloid, especially, its association with extrarenal systemic light chain amyloidosis. We found intratubular amyloid in 17 cases (17/60, 28%) and it was more frequent in patients with λ light chain gammopathy (13/17 in the 'intratubular amyloid' group vs 19/43 in the 'no intratubular amyloid' group, P=0.02). Pathological examination of extrarenal specimens showed that intratubular amyloid was significantly associated with the occurrence of systemic light chain amyloidosis (5/13 in the 'intratubular amyloid' group vs 0/30 in the 'no intratubular amyloid' group, P=0.001). Our results indicate that first, intratubular amyloid is not a rare finding in kidney biopsies of patients with light chain cast nephropathy, and, second, it reflects an amyloidogenic capacity of light chains that can manifest as systemic light chain amyloidosis. Thus, intratubular amyloid should be systematically screened for in kidney biopsies from patients with light chain cast nephropathy and, if detected, should prompt a work-up for associated systemic light chain amyloidosis.

[The concurrence of light-chain deposition disease, AL-amyloidosis, and cast nephropathy in a patient with multiple myeloma]

Despite of the fact that their clinical manifestations are similar, AL-amyloidosis (AL-A) and light chain deposition disease (LCDD) are individual nosological entities in view of considerable differences in their pathogenesis and pathomorphology. The paper describes a rare case of the concurrence of LCDD and AL-A in a patient with multiple myeloma. Clinically, there was dialysis-dependent renal failure, flail leg syndrome, myocardiopathy, and rhabdomyolysis. At the disease onset, his nephrobiopsy specimen could diagnose LCDD and myeloma or cast nephropathy. The disease was characterized by an aggressive course. Despite the administration of innovative agents, the patient had a short-term remission and died from disease progression. Autopsy additionally revealed amyloid deposition in the heart and kidney. The development of AL-A in the presence of prior LCDD may reflect the progression of the tumor and the appearance of an additional subclone of plasma cells that produce amyloidogenic light chains. The uncommonness of this case is that renal amyloid was found in the tubular casts and absent in the glomeruli, which may be considered as a special form--tubular AL-amyloidosis.

The clinical spectrum of pure Bence Jones proteinuria. A study of 66 patients

Sixty-six consecutive patients exhibiting isolated urinary excretion of monoclonal free light chains, i.e. Bence Jones protein (BJP), on screening investigation for serum and urine monoclonal immunoglobulins were studied in order to better define the spectrum of immunoproliferative disorders associated with such a protein abnormality. The typical plasma cell neoplasms accounted for only one third of the cases, multiple myeloma (MM) and systemic amyloidosis (AL) being diagnosed in 18% and 15% of the patients, respectively. Eighteen (27%) of the patients were recognized as having malignant nonHodgkin's lymphomas (NHL), 21 (32%) had chronic lymphocytic leukemia (CLL), and 2 (3%) had hairy cell leukemia (HCL). Three patients (5%) without apparent evidence of any malignant immunoproliferative disease were classified as having a monoclonal gammopathy of undetermined significance (MGUS). The greatest urinary concentrations of BJP were found in plasmacytic neoplasms, the daily excretion of MM patients being significantly higher than that of AL patients. Considerably lower BJP outputs were recorded in the other diseases, the lowest ones being associated with MGUS. NHL patients had a daily excretion four times higher as compared with that of CLL patients. The distribution of NHL by histologic type was: follicular center cell lymphomas (FCCL) 39%, small lymphocytic lymphoma (SLL) 33%, immunoblastic lymphoma (IBL) 17%, and plasmacytoid lymphocytic lymphoma (PLL) 11%. The highest BJP levels were found in PLL, and the lowest ones in FCCL. In CLL patients the amount of urinary BJP correlated significantly with the tumor load, as estimated by the number of enlarged lymphoid areas. The study suggests that detection and measurement of isolated urinary BJP may provide useful data for the clinical evaluation of a wide spectrum of immunoproliferative disorders.