Intra-tubular amyloidosis

Mono/polyclonal free light chains as challenging biomarkers for immunological abnormalities

Free light chain (FLC) kappa (k) and lambda (λ) consist of low molecular weight proteins produced in excess during immunoglobulin synthesis and secreted into the circulation. In patients with normal renal function, over 99% of FLCs are filtered and reabsorbed. Thus, the presence of FLCs in the serum is directly related to plasma cell activity and the balance between production and renal clearance. FLCs are bioactive molecules that may exist as monoclonal (m) and polyclonal (p) FLCs. These have been detected in several body fluids and may be key indicators of ongoing damage and/or illness. International guidelines now recommend mFLC for screening, diagnosis and monitoring multiple myeloma and other plasma cell dyscrasias. In current clinical practice, FLCs in urine indicate cast nephropathy and other renal injury, whereas their presence in cerebrospinal fluid is important for identifying central nervous system inflammatory diseases such as multiple sclerosis. Increased pFLCs have also been detected in various conditions characterized by B cell activation, i.e., chronic inflammation, autoimmune disease and HCV infection. Monitoring the coronavirus (COVID-19) pandemic by analysis of salivary FLCs presents a significant opportunity in clinical immunology worthy of scientific pursuit.

Renal amyloidosis: Pathogenesis

For many years amyloidosis was considered an extremely rare, somewhat mysterious disease. However, in the last 2-3 decades its pathogenesis, particularly that of renal amyloidosis has been carefully dissected in the research laboratory using in-vitro and, to a lesser extent, in-vivo models. These have provided a molecular understanding of sequential events that take place in the renal mesangium leading to the formation of amyloid fibrils and eventual extrusion into the mesangial matrix, which itself becomes seriously damaged and, in due time, replaced by the fibrillary material. Amyloid, once considered to be an "inert" substance, has been proven to be involved in crucial biological processes that result in the destruction and eventual replacement of normal renal constituents. This review centers on mechanisms involved in the renal glomerular amyloidosis to understand its pathogenesis.

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.

Renal amyloidosis with emphasis on the diagnostic role of electron microscopy

Our understanding of renal diseases with structured deposits has improved in the last two decades with the development of new diagnostic techniques that also changed the role of ultrastructural pathology in diagnostic decision-making. This review article addresses the current role of electron microscopy in the evaluation of structured deposits and discusses the impact of new developments. The diagnosis in a subset of structured deposits, amyloidosis, relies on morphologic and tinctorial characteristics at the light microscopic level. Congo red staining of tissue with demonstrable birefringence upon polarization has been regarded as the mainstay during tissue evaluation; however, there are pitfalls that must be considered, and electron microscopy remains a crucial adjunct investigative tool. Ultrastructurally the amyloid fibrils are unique with their characteristic appearance. They are randomly arranged, rigid, criss-crossing, non-branching, 7-15 nm (0.07-0.15 um) in diameter and of variable length. The morphology of fibrils is very similar in the different types of amyloidosis. By scanning electron microscopy amyloid fibrils appear artfully displayed. Immunofluorescence and immunohistochemical stains can be used to characterize the type of amyloidosis while mass spectroscopy is extremely useful in cases where typing of the amyloid using the above-mentioned techniques is difficult or equivocal.

An autopsy case of amyloid tubulopathy exhibiting characteristic spheroid-type deposition

An 84-year-old woman with a history of haemodialysis for renal failure from approximately 1 year before death. Autopsy revealed numerous spheroid-type amyloid deposits in the kidney that were observed mainly in the interstitium but not the glomeruli and vessels. In addition, intracytoplasmic small globular amyloid deposits in the proximal tubules in addition to amyloid casts were identified. Immunohistochemistry and proteomic analyses indicated these deposits were composed of λ light chains. Amyloid deposition was also found in the lung and heart. λ-type monoclonal protein was detected in her serum and increased numbers of CD138-positive cells with λ-restriction was observed in the bone marrow. The case was diagnosed as amyloid tubulopathy (AT) associated with systemic ALλ amyloidosis related to plasma cell neoplasm. This case indicates that AT is associated with ALλ amyloidosis, which developed systemically with characteristic amyloid deposition forms. These pathological features may be associated with her rapid progressive renal failure.

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.

Amyloid Proximal Tubulopathy and Amyloid Casts: An Unusual Finding in Multiple Myeloma

Patients with multiple myeloma (MM) often develop renal manifestations. The majority of cases present as cast nephropathy, amyloid light-chain (AL) amyloidosis, and monoclonal immunoglobulin deposition disease. AL amyloidosis usually involves the glomeruli, blood vessels, and interstitium. It is extremely uncommon to find isolated intratubular deposition of AL amyloid. Our patient presented with rapid worsening of renal function due to isolated intratubular deposition of AL amyloid, where the biopsy revealed amyloid proximal tubulopathy and amyloid cast nephropathy. Our case provides new insights into the complicated pathophysiology of the abnormal light chains in MM. This case is, to our knowledge, the second case of amyloid proximal tubulopathy reported in literature.

[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.

Amyloid nephropathy

Amyloidosis is an uncommon disease that is characterized by abnormal extracellular deposition of misfolded protein fibrils leading to organ dysfunction. The deposited proteins display common chemical and histologic properties but can vary dramatically in their origin. Kidney disease is a common manifestation in patients with systemic amyloidosis with a number of amyloidogenic proteins discovered in kidney biopsy specimens. The emergence of mass spectrometry-based proteomics has added to the diagnostic accuracy and overall understanding of amyloidosis. This in-depth review discusses the general histopathologic features of renal amyloidosis and includes an in-depth discussion of specific forms of amyloid affecting the kidney.

Amyloid proximal tubulopathy: a novel form of light chain proximal tubulopathy

Light chain proximal tubulopathy is a paraproteinemic-related kidney disease most commonly seen in patients with a plasma cell dyscrasia. The classic description is that of proximal tubules with kappa-restricted intracytoplasmic crystals in a patient with a clinical Fanconi’s syndrome. Recently, other variants of light chain proximal tubulopathy have been described including those without crystal formation. We expand the morphologic spectrum in this report of a patient who presented with acute renal failure, proteinuria and hematuria. Biopsy revealed proximal tubulopathy in which the proximal tubules show intracytoplasmic amyloid formation. This is the first description, to our knowledge, of amyloid proximal tubulopathy.

Telocytes in human isolated atrial amyloidosis: ultrastructural remodelling

The human heart can be frequently affected by an organ-limited amyloidosis called isolated atrial amyloidosis (IAA). IAA is a frequent histopathological finding in patients with long-standing atrial fibrillation (AF). The aim of this paper was to investigate the ultrastructure of cardiomyocytes and telocytes in patients with AF and IAA. Human atrial biopsies were obtained from 37 patients undergoing cardiac surgery, 23 having AF (62%). Small fragments were harvested from the left and right atrial appendages and from the atrial sleeves of pulmonary veins and processed for electron microscopy (EM). Additional fragments were paraffin embedded for Congo-red staining. The EM examination certified that 17 patients had IAA and 82% of them had AF. EM showed that amyloid deposits, composed of characteristic 10-nm-thick filaments were strictly extra-cellular. Although, under light microscope some amyloid deposits seemed to be located within the cardiomyocyte cytoplasm, EM showed that these deposits are actually located in interstitial recesses. Moreover, EM revealed that telopodes, the long and slender processes of telocytes, usually surround the amyloid deposits limiting their spreading into the interstitium. Our results come to endorse the presumptive association of AF and IAA, and show the exclusive, extracellular localization of amyloid fibrils. The particular connection of telopodes with amyloid deposits suggests their involvement in isolated atrial amyloidosis and AF pathogenesis.

Renal lesions associated with plasma cell dyscrasias: practical approach to diagnosis, new concepts, and challenges

CONTEXT

Patients with plasma cell dyscrasias (myeloma) may exhibit a variety of renal manifestations as a result of damage from circulating light- and heavy-chain immunoglobulin components produced by the neoplastic plasma cells. The renal alterations can occur in any of the renal compartments, and in a significant number of the cases more than one compartment is affected. Research in the laboratory has helped considerably in providing a solid conceptual understanding of how renal damage occurs.

OBJECTIVES

To detail advances that have been made in the diagnosis of these conditions and to provide an account of research accomplishments that have solidified diagnostic criteria. The new knowledge that has been acquired serves to provide a solid platform for the future design of new therapeutic interventions aimed at ameliorating or abolishing the progressive renal damage that typically takes place.

DATA SOURCES

Translational efforts have substantially contributed to elucidate mechanistically the molecular events responsible for the renal damage. The spectrum of renal manifestations associated with plasma cell dyscrasias has expanded significantly in the last 10 years. Diagnostic criteria have also been refined. This information has been summarized from work done at several institutions.

CONCLUSIONS

A number of significant challenges remain in the diagnosis of these conditions, some of which will be discussed in this article. Dealing with these challenges will require additional translational efforts and close cooperation between basic researchers, clinicians, and pathologists in order to improve the diagnostic tools available to renal pathologists and to acquire a more complete understanding of clinical and pathologic manifestations associated with these conditions.