Amyloid light chain amyloidosis involving the kidneys is not uncommon in patients with monoclonal gammopathy. The mainstay of treatment of amyloid light chain amyloidosis is autologous hematopoietic stem cell transplantation. Evidence that the autologous hematopoietic stem cell transplantation has been successful is the absence of free monoclonal light chains in serum and urine. Herein, we report 2 cases of progressive renal amyloid light chain amyloidosis after autologous hematopoietic stem cell transplantation, documented by kidney biopsy, despite the absence of monoclonal protein in the serum and urine. Kidney function declined progressively in both patients. During that time, numerous immunofixation and protein electrophoresis test results were negative for monoclonal protein, both in serum and urine, concealing the progression of the amyloidosis. We conclude that close monitoring of kidney function is warranted following autologous hematopoietic stem cell transplantation in patients with amyloid light chain amyloidosis, even with negative results from monoclonal protein testing. Unexplained, worsening renal function warrants a kidney biopsy to assess whether retreatment of the monoclonal gammopathy is indicated.
Systemic amyloid light chain (AL) amyloidosis is a condition in which the amyloid protein (amyloidogenic light chain) is abnormally deposited in the extracellular matrix of multiple organs. Approximately two-thirds of patients with AL amyloidosis are male. Most patients are older than 40 years.1,2 The prognosis is generally poor; cardiac or renal failure are the main causes of death.3 The treatment options for AL amyloidosis include chemotherapy, bone marrow transplantation, or autologous hematopoietic stem cell transplantation (AHSCT).1,3 High-dose melphalan therapy, combined with either peripheral blood or bone marrow stem cell transplantation, is effective in most patients, with amyloid deposition remaining stable or decreasing over time.4,5 Remission of AL amyloidosis is defined as a complete hematologic response (ie, no evidence of serum monoclonal free light chains).2 Remission rates with these treatment modalities vary but have been reported6 as high as 40%. Here, we describe 2 patients cared for at our institution who, after AHSCT, experienced slowly declining renal function because of massive glomerular AL deposits, as determined by kidney biopsy. Remarkably, results from repeated testing of blood and urine for free monoclonal light chains were negative. Failure of amyloidosis to regress after AHSCT, even though free monoclonal light chains were no longer detectable, has been previously reported.7,8 However, to our knowledge, this is the first report to show that severe, progressive glomerular amyloidosis can occur after AHSCT, even though both patients met the criteria for successful AHSCT, which include negative testing for free monoclonal light chains by serum protein electrophoresis; serum immunofixation; urine immunofixation; a ratio of free monoclonal light chains in the serum within reference range; and a bone marrow biopsy showing less than 5% plasma cells.9,10
REPORT OF CASES
Patient 1 was an 80-year-old white man, who presented in 2002 with proteinuria of 12.6 g/24 h and serum creatinine of 1.4 mg/dL. A kidney biopsy was performed at that time. Light microscopy showed as many as 33 glomeruli. Up to 10 or 11 glomeruli were globally sclerotic, those with open capillary loops were mildly enlarged, and they had mild mesangial expansion. Small deposits of homogenous, amorphous, gray-pink material, which was negative for periodic acid–Schiff and silver staining, were seen in the mesangium. These deposits stained positive for Congo red, and they showed apple-green birefringence under polarized light. No amyloid deposits were seen in the interstitium, and only focal and small amyloid deposits were noted in the arterial wall. The degree of chronic kidney injury was moderate, with approximately 30% interstitial fibrosis and tubular atrophy. No relevant interstitial inflammation was seen. Amyloid deposits had diameter of 9.85 nm. Immunofluorescence was unremarkable. A bone marrow biopsy performed at the same time showed mild plasmacytosis (5%). In situ hybridization for κ and λ messenger RNA (mRNA) demonstrated a mild λ predominance, but the κ:λ ratio was insufficiently skewed for definitive determination of clonality. Congo red stain results were negative in the bone marrow biopsy. Serum and urine immunofixation showed free λ light chain in the serum and 507 mg/24 h of free λ light chain in the urine. This represented 4% of the total urine protein.
The patient received AHSCT in October 2002. Proteinuria decreased to 2.5–2.8 g/24 h and remained stable until 2011. No free light chains were detected in the urine during that time. For that reason, testing for monoclonal proteins was stopped in 2008. Serum creatinine level was stable in the range of 2.5 to 3.0 mg/dL (reference range, 0.6–1.2 mg/dL; to convert to micromoles per liter, multiply by 88.4) until April 2011, when the patient presented with increased proteinuria (3.0 g/24 h) and an elevated serum creatinine (3.5 mg/dL) (Figure 1, A and B). A renal biopsy performed in July 2011 showed progressive renal amyloidosis with prominent amyloid deposits obliterating all the glomeruli (Figure 3). Amyloid deposits were also seen in the surrounding fibroadipose tissue, which indicated extrarenal involvement. Significantly increased amyloid deposits were seen in the arterial wall, whereas only mild and focal vascular deposits were noted in the first biopsy. The degree of chronic kidney injury was advanced, with more than 80% interstitial fibrosis and tubular atrophy (only 30% in the biopsy performed 9 years earlier). Immunofluorescence indicated predominant λ light chain staining in the amyloid deposits. Mass spectrometry confirmed that patient 1 had AL λ light chain amyloidosis involving the kidney. A bone marrow biopsy performed at that time showed few plasma cells (3% on the aspirate smear; 0.1% by flow cytometry). A small subset of plasma cells expressed CD56, but clonality of those cells could not be determined because of low numbers. Clinical workup in September 2011 indicated the reappearance of free λ light chains in the urine by immunofixation. Remarkably, the amount of free λ light chain was less than that measured in 2002. Serum protein immunofixation results were negative for monoclonal protein. However, a serum free light chain assay demonstrated increases in both κ (28.9 mg/L; reference range, 3.3–19.4 mg/L) and λ (108 mg/L; reference range, 5.71–26.30 mg/L) light chains with a κ:λ free light chain ratio of 0.27 (reference range, 0.26–1.65), which was still within the reference range. By September 2011, the proteinuria had increased to 4.7 g/24 h, with 90 mg/24 hours (1.9%) of monoclonal free λ light chain (Figure 1, B). Unfortunately, the patient expired in December 2011 from severe gastrointestinal bleeding secondary to a duodenal ulcer. No autopsy was performed.
Patient 2 was a 58-year-old white woman, who was first diagnosed with amyloidosis in the liver on a biopsy performed in December 2005. The liver biopsy showed sinusoidal and arterial amyloid deposits. Immunohistochemistry indicated positive staining for λ light chain and negative staining for κ light chain. A bone marrow biopsy performed at that time showed hypocellular bone marrow, with a λ clonal plasma cell population (6%) shown by immunohistochemistry, and focal amyloid deposition in the vascular wall. Urine immunofixation electrophoresis results at that time were positive for monoclonal λ light chains, and the patient had proteinuria of 1.352 g/24 hours (Figure 1, D). No quantitative data for free light chain urinary excretion were available. A bone marrow biopsy identified λ-restricted plasma cell neoplasm with very focal Congo red-positive amyloid deposits in the blood vessels. Her serum creatinine was 2 mg/dL in December 2005.
The patient underwent AHSCT in February 2006. Shortly after the AHSCT, the patient experienced an episode of acute kidney injury, which was attributed to the engraftment syndrome. Serum creatinine returned to baseline levels after resolution of the acute kidney injury and was in the range of 1.4 to 1.9 mg/dL until October 2007, when she presented with a serum creatinine of 2.8 mg/dL (Figure 1, C). A kidney biopsy was performed. Glomeruli contained moderate mesangial amyloid deposits. Amyloid deposits were not seen in the vasculature. The degree of chronic kidney injury was mild to moderate with approximately 10% to 20% interstitial fibrosis and tubular atrophy. Immunofluorescence showed a predominance of λ light chain staining in the amyloid deposits, which had a mean diameter of 9 nm by electron microscopy. A bone marrow biopsy performed at that time showed normocellular bone marrow with small clusters of plasma cells (2%). Flow cytometry did not reveal an abnormal cell population.
Serum creatinine levels continued to increase. When serum creatinine reached 4.7 mg/dL (August 2009), the patient underwent a second kidney biopsy (Figure 1, C). All glomeruli were obliterated by prominent amyloid deposits. Amyloid deposits were also present in the renal vessels, including arteries and arterioles, and in the interstitium. The degree of chronic kidney injury was advanced, with more than 80% interstitial fibrosis and tubular atrophy. Immunofluorescence indicated that the amyloid deposits were stained predominantly with λ light chain, and they had the mean diameter of 9.6 nm by electron microscopy. These morphologic findings indicated significantly increased amyloid deposits and progressive chronic kidney injury, as compared with the kidney biopsy performed 2 years earlier. Mass spectrometry confirmed that the amyloid deposits were the AL λ type. A bone marrow biopsy performed at that time showed normocellular bone marrow with a small amount of amyloid deposits and no increase in plasma cells. Polyclonal plasma cells accounted for less than 2% of the cell population. Although the amyloid deposits were described as a small amount, they were found in the periosteal fibroconnective tissue and in a blood vessel. Because of the continuing decline in renal function, the patient was placed on dialysis in December 2009.
Repeated urine and serum protein electrophoresis and immunofixation test results had been negative until that point. Serum free light chain assays performed after AHSCT showed normal free κ and λ light chain levels until March 2009, when free κ light chain levels first become elevated. After January 2010, both serum free κ and λ light chains were elevated, but the serum κ:λ free light chain ratio was within reference limits (Figure 3).
DISCUSSION AND REVIEW OF THE LITERATURE
To our knowledge, this is the first report describing significant progression of renal AL amyloidosis in patients with “successful” autologous stem-cell transplant based on the absence of detectable monoclonal protein in the serum and urine.
Amyloid is an aberrant form of a normal protein in the body, produced when fragments of the protein join to create β-pleated sheets. Amyloid deposition can occur in any organ in the body. The kidney is one of the most common organs involved by amyloidosis, especially by AL amyloidosis, which contains immunoglobulin light chains produced by abnormal clonal plasma cells.1 The incidence rate of AL amyloidosis in the United States is approximately 12 cases per 1 million per year.2,11
Treatment of AL amyloidosis with high-dose melphalan and stem cell transplantation has proven effective, with a sustained clinical response and reversal of amyloid-related organ dysfunction.12 This treatment modality has higher response rates and improved overall survival than does standard chemotherapy. The best outcomes have been reported in patients who achieve complete response to high-dose primary chemotherapy, including improvement of organ-related disease.11 Clinical remission or recurrence is monitored by testing for increased free light chain in the serum or urine. Protein electrophoresis or immunofixation are the standard methods used.9,10 Free light chain assay is a more sensitive methodology, and it is also performed to monitor patients with multiple myeloma (MM) or monoclonal gammopathy of undetermined significance.9
In our institution, serum free, light chain levels are tracked as a response biomarker in patients with light chain amyloidosis. The sensitivity of this biomarker can be reduced in the setting of renal insufficiency. Therefore, in patients with kidney disease, the κ:λ ratio becomes important, as opposed to the involved free light chain levels, per se, because uninvolved free light chain levels can be elevated in patients with kidney disease as well (as we had seen in our patients). Criteria for a “successful” stem cell transplant include (1) the patient surviving the transplant (stem cell transplantation has approximately 10% treatment-related mortality); (2) the involved, free light chain (typically λ) being in the reference range; and (3) the κ:λ ratio being normal or preferably being more than 1.0. Patients typically are monitored monthly for a few months after stem cell transplant, then they are monitored every 3 months, if no abnormal laboratory data are found.
Based on the National Comprehensive Cancer Network clinical practice guidelines in oncology criteria, a complete hematologic response includes negative serum and urine immunofixation, κ:λ free light chain ratio within reference range, and normal bone marrow biopsy findings. Serum electrophoresis alone may be an inadequate determinant, because 50% of cases do not show a monoclonal spike.9 A complete renal response includes a 50% decrease in 24-hour urinary protein excretion in the absence of worsening creatinine clearance by 25% or more or an increase in serum creatinine by 0.5 g/dL or more.13 The absence of monoclonal protein by different assays in some patients with monoclonal gammopathies has been reported. Katzmann et al14 found that approximately 1.5% of patients with diagnosed monoclonal gammopathy had negative results on different assays, including serum and urine protein electrophoresis, serum and urine immunofixation, and quantitative serum free light chain assays, similar to the patients reported herein.
The progression of amyloid deposition following stem cell transplantation could suggest a sort of failure in the treatment modality. Subsequent renal biopsies are not usually recommended for follow-up in patients after AHSCT. However, both of our patients showed worsening renal function with increasing serum creatinine without any indication of new or worsening serum or urinary monoclonal protein. Our case report shows the importance of continued serum creatinine and 24-hour urinary excretion testing in patients with light chain amyloidosis after AHSCT. If these tests show increasing serum creatinine or urinary excretion of protein, then a follow-up renal biopsy is warranted to assess renal injury and the possible progression of renal amyloid.
There is a previous report7 of stable renal AL amyloid deposits 3 years after autologous blood stem cell transplant that caused the monoclonal proteins to become undetectable in the serum and urine. The authors describe 2 patients with biopsy-proven AL amyloidosis involving the kidney, secondary to IgA λ monoclonal gammopathy. The patients received high-dose melphalan treatment and autologous blood stem-cell transplantation. At the time of second kidney biopsies, performed 3 years later, both patients were in clinical remission with no detectable monoclonal protein in the serum or urine and a percentage of plasma cells in the bone marrow within the reference range. Proteinuria was decreased in both patients. However, second kidney biopsies showed persistent amyloid deposits in both patients.7 A case report by Yamazaki et al8 describes a patient with primary systemic AL amyloidosis who was in clinical remission after autologous peripheral blood stem-cell transplantation. Despite disappearance of proteinuria, the patient still had approximately the same number of amyloid deposits in a repeat kidney biopsy performed 2 years later.8 There has also been a report of resorption of amyloid deposits in the kidney following treatment of MM.15 Thus, a patient, who was placed on dialysis because of severe renal AL amyloidosis, became dialysis-free 2 years later after several courses of chemotherapy. Repeat kidney biopsy performed 3 years later showed markedly decreased amyloid deposition in the kidney.15 Our report, however, is the first, to our knowledge, to document severe progression of renal amyloidosis following therapy for AL amyloidosis, even though monoclonal proteins were not detectable in either serum or urine.
The pathogenesis of the progressive amyloidosis reported here is not clear. Nevertheless, we suggest the following: perhaps, the amount of paraprotein in the serum or urine was pathologic, but less than the limits of detection. It also is possible that the circulating monoclonal light chains in these patients were extremely amyloidogenic, leading to renal amyloidosis, even in very small, undetectable quantities in the serum and their absence in the urine. The absence of monoclonal free light chains in the urine can be explained by the trapping of the monoclonal light chain in the glomerulus without their being released in the urine. Alternatively, the levels of paraprotein may have been in flux and, unfortunately, they were tested only when the fluctuations were at low ebb. To test this hypothesis would require more frequent testing for monoclonal proteins after AHSCT for AL amyloid. In light of our experience, this may be a hypothesis worth testing. Yet another consideration could be that the stem cell transplantation, for some reason, might have failed to eliminate the neoplastic plasma cell clones in our 2 cases, causing continued and progressive amyloid deposition.
Typically, patients are evaluated and screened for free light chains monthly after AHSCT, then every 3 months, if they are clinically stable or improving.9 Similar guidelines were followed in both patients described herein. We believe that renal function is crucial for assessment of amyloidosis progression in the kidney in patients with monoclonal gammopathy, regardless of the presence of monoclonal protein in the serum or urine. The guidelines dictating follow-up and screening for serum or urine free light chains should include renal biopsy for certain patients who show signs of renal dysfunction, even in the absence of free light chain deposition.
This study was supported, in part, by the start-up funding provided to Dr Brodsky by the Department of Pathology, The Ohio State University.
The authors have no relevant financial interest in the products or companies described in this article.