Dysproteinemia-related nephropathy associated with crystal-storing histiocytosis

Combined crystal-storing histiocytosis, light chain proximal tubulopathy, and light chain crystalline podocytopathy in a patient with multiple myeloma: a case report and literature review

BACKGROUND

Crystal-storing histiocytosis (CSH), light chain proximal tubulopathy (LCPT), and light chain crystalline podocytopathy (LCCP) are rare complications of multiple myeloma (MM) or monoclonal gammopathy of renal significance, and their diagnoses are challenging.

CASE PRESENTATION

In this case, a 69-year-old Chinese woman presented with suspicious Fanconi syndrome with renal insufficiency. Immunofixation electrophoresis of both serum and urine revealed elevated immunoglobulin G kappa (IgGkappa) and kappa light chain. Bone marrow aspirate revealed 15% plasma cells with considerable cytoplasmic granular inclusions and needle-shaped crystals. Renal biopsy confirmed the final pathologic diagnosis of kappa-restricted CSH, combined LCPT and LCCP by immunoelectron microscopy. A number of special casts were present which could easily be misdiagnosed as light chain cast nephropathy. Immunofluorescence on frozen tissue presented false negative for kappa light chain, as ultimately proven by paraffin-embedded tissue after pronase digestion. MM and CSH were diagnosed, and two cycles of chemotherapy were given. The patient subsequently refused further chemotherapy, and her renal function remained relatively stable during a 2.5-year follow-up period.

CONCLUSIONS

In conclusion, we report a rare case of generalized kappa-restricted CSH involving bone marrow and kidney, combined with LCPT and LCCP, provide a comprehensive summary of renal CSH, and propose a new nomenclature of monoclonal immunoglobulin-induced crystalline nephrology. The presentation of monoclonal immunoglobulin and Fanconi syndrome should suggest the presence of monoclonal immunoglobulin-induced crystalline nephrology. Use of paraffin-embedded tissue after pronase digestion and immunoelectron microscopy is beneficial to improve the sensitivity of diagnosis.

Crystal-Storing Histiocytosis: The Iceberg of More Serious Conditions

Crystal-storing histiocytosis is a rare condition that is histologically characterized by intracellular cytoplasmic crystalline inclusions. It usually presents monoclonal immunoglobulins that deposit within histiocytes, which accumulate and affect different organs of the human body and are commonly associated with lymphoproliferative conditions, especially those with plasmacytic differentiation. The prognosis of this condition is variable and related to the underlying clinical disease. In this review article, we aim to describe and discuss the clinical and pathological characteristics of crystal-storing histiocytosis based on the available literature and to provide a thorough differential diagnosis.

The Crystalline Nephropathies

Crystalline nephropathies are a unique form of kidney disease characterized by the histologic finding of intrarenal crystal deposition. The intrinsic nature of some molecules and ions combined with a favorable tubular fluid physiology leads to crystal precipitation and deposition within the tubular lumens. Crystal deposition promotes kidney injury through tubular obstruction and both direct and indirect cytotoxicities. Further kidney injury develops from inflammation triggered by these crystals. From a clinical standpoint, the crystalline nephropathies are associated with abnormal urinalysis and urinary sediment findings, tubulopathies, acute kidney injury (AKI), and/or chronic kidney disease (CKD). Urine sediment examination is often helpful in alerting clinicians to the possibility of crystal-related kidney injury. The identification of crystals within the kidneys on biopsy by pathologists prompts clinicians to evaluate patients for medication-related kidney injury, dysproteinemia-related malignancies, and certain inherited disorders. This review will focus on the clinical and pathologic aspects of these 3 categories of crystalline nephropathies.

Glucocorticoid-dependent Tubulointerstitial Nephritis with IgM-positive Plasma Cells Presenting with Intracellular Crystalline Inclusions within the Rough Endoplasmic Reticulum

Tubulointerstitial nephritis (TIN) with IgM-positive plasma cells (IgMPC-TIN) is an autoimmune kidney disease characterized by IgM/CD138-double-positive plasma cell infiltration in the tubulointerstitium. A 50-year-old man developed IgMPC-TIN and presented with crystalline inclusions in the rough endoplasmic reticulum. Intracellular crystal formation is a rare finding in paraprotein-related kidney diseases, but this case showed no pathogenic monoclonal immunoglobulin. Prednisolone (PSL, 30 mg) improved the TIN, but PSL tapering resulted in the recurrence of TIN. Combination therapy with 15 mg PSL and 150 mg mizoribine ultimately stabilized TIN. This case offers original evidence concerning the pathophysiology and treatment strategy of IgMPC-TIN.

Immunoglobulin-Storing Histiocytosis: A Case Based Systemic Review

Crystal-storing histiocytosis (CSH) is a rare event in disorders associated with monoclonal gammopathy and is mostly associated with the accumulation of immunoglobulins (Igs) in the cytoplasm of histiocytes. In this article, we present a case of a 75-year-old female with IgG kappa monoclonal gammopathy of undetermined significance (MGUS) and signs of a non-crystallized version of immunoglobulin-storing histiocytosis (IgSH) in a vertebra corpus. Furthermore, we performed a literature review based on all cases of storing histiocytosis identified by literature search between 1987 and 2020 and identified 140 cases in total. The median age at diagnosis was 60 years (range 18–91), with an equal sex distribution (51% men). The majority of the patients had an underlying neoplastic B-cell disorder, most often multiple myeloma (MM), MGUS, or lymphoplasmacytic lymphoma (LPL). The main affected organ systems or tissue sites were bone (n = 52), followed by head and neck (n = 31), kidney (n = 23), lung (n = 20), and gastrointestinal (GI)-tract (n = 18). IgG was the main immunoglobulin class involved, and most cases were associated with kappa light chain expression. We conclude that IgSH is a rare disease entity but should be considered with unusual findings in several organ systems associated with monoclonal gammopathy, especially with kappa light chain expression.

Combined light chain crystalline tubulopathy, podocytopathy, and histiocytosis associated with Bence-Jones κ protein diagnosed via immuno-electron microscopy

We herein report a case of a combined crystalline light chain tubulopathy, podocytopathy, histiocytosis, and cast nephropathy in a patient with monoclonal gammopathy of renal significance (MGRS). A 66-year-old female with impaired renal function was referred to our department. Despite intravenous fluid resuscitation, the kidney function worsened progressively; thus, a kidney biopsy was performed. The kidney biopsy revealed light chain proximal tubulopathy (LCPT) with crystals, light chain crystal podocytopathy (LCCP), crystal-storing histiocytosis (CSH), and light chain cast nephropathy (LCCN). Of note, LCCP and CSH were diagnosed via electron microscopy. Serum and urine immunoelectrophoresis (IEP) revealed the presence of monoclonal Bence-Jones protein and free κ light chains. Bone marrow aspiration showed < 10% plasma cell proliferation. Thus, we had encountered a rare case in which a variety of kidney lesions were combined with MGRS. Most of the LCPT, LCCP, and CSH cases show monoclonal IgG κ, while our case showed Bence-Jones protein κ.

Renal crystal-storing histiocytosis involving glomeruli - A comprehensive clinicopathologic analysis

Crystal-storing histiocytosis (CSH) is a rare manifestation of monoclonal gammopathy in which histiocytes containing monoclonal proteins in their cytoplasm are found in various organs of the body including the kidney. Within the kidney, these monoclonal crystal-laden histiocytes have been described to occur in the interstitium (most commonly) or in the glomerular mesangium. CSH within glomerular capillary loops has rarely been reported. We describe three cases of CSH primarily affecting the glomerular capillaries and review the literature of CSH in general. Twenty cases of CSH involving the kidney are present in the literature; three describe CSH in glomeruli, only one of which showed histiocytes predominantly in glomerular capillary loops, while 15 had predominantly or solely interstitial CSH. Most cases involve IgG kappa crystals with only one case involving lambda light chain. Patients with CSH predominantly involving the glomerular capillaries showed a trend toward lower serum creatinine and proteinuria at presentation, and several patients with CSH lacked a definitive diagnosis of a monoclonal gammopathy at the time of diagnosis, emphasizing the role that kidney biopsy and particularly electron microscopy play in diagnosis of this entity.

The Complexity and Heterogeneity of Monoclonal Immunoglobulin-Associated Renal Diseases

Monoclonal gammopathies are characterized by the overproduction of monoclonal Ig (MIg) detectable in the serum or urine resulting from a clonal proliferation of plasma cells or B lymphocytes. The underlying hematologic conditions range from malignant neoplasms of plasma cells or B lymphocytes, including multiple myeloma and B-cell lymphoproliferative disorders, to nonmalignant small clonal proliferations. The term MGUS implies presence of an MIg in the setting of a "benign" hematologic condition without renal or other end organ damage. The term MGRS was recently introduced to indicate monoclonal gammopathy with MIg-associated renal disease in the absence of hematologic malignancy. Most MIg-associated renal diseases result from the direct deposition of nephrotoxic MIg or its light- or heavy-chain fragments in various renal tissue compartments. Immunofluorescence microscopy is essential to identify the offending MIg and define its tissue distribution. Mass spectrometry is helpful in difficult cases. Conditions caused by direct tissue deposition of MIg include common disorders, such as cast nephropathy, amyloidosis, and MIg deposition diseases, as well as uncommon disorders, such as immunotactoid glomerulopathy, proliferative GN with MIg deposits, light-chain proximal tubulopathy, and the rare entities of crystal-storing histiocytosis and crystalglobulinemia. Indirect mechanisms of MIg-induced renal disease can cause C3 glomerulopathy or thrombotic microangiopathy without tissue MIg deposits. Treatment of MIg-associated renal disease is aimed at eliminating the clonal plasma cell or B-cell population as appropriate. Both the renal and the underlying hematologic disorders influence the management and prognosis of MIg-associated renal diseases.

Novel mesostructured inclusions in the epidermal lining of Artemia franciscana ovisacs show optical activity

Background

Biomineralization, e.g., in sea urchins or mollusks, includes the assembly of mesoscopic superstructures from inorganic crystalline components and biopolymers. The resulting mesocrystals inspire biophysicists and material scientists alike, because of their extraordinary physical properties. Current efforts to replicate mesocrystal synthesis in vitro require understanding the principles of their self-assembly in vivo. One question, not addressed so far, is whether intracellular crystals of proteins can assemble with biopolymers into functional mesocrystal-like structures. During our electron microscopy studies into Artemia franciscana (Crustacea: Branchiopoda), we found initial evidence of such proteinaceous mesostructures.

Results

EM preparations with high-pressure freezing and accelerated freeze substitution revealed an extraordinary intracellular source of mesostructured inclusions in both the cyto-and nucleoplasm of the epidermal lining of ovisacs of A. franciscana. Confocal reflection microscopy not only confirmed our finding; it also revealed reflective, light dispersing activity of these flake-like structures, their positioning and orientation with respect to the ovisac inside. Both the striation of alternating electron dense and electron-lucent components and the sharp edges of the flakes indicate self-assembly of material of yet unknown origin under supposed participation of crystallization. However, selected area electron diffraction could not verify the status of crystallization. Energy dispersive X-ray analysis measured a marked increase in nitrogen within the flake-like inclusion, and the almost complete absence of elements that are typically involved in inorganic crystallization. This rise in nitrogen could possibility be related to higher package density of proteins, achieved by mesostructure assembly.

Conclusions

The ovisac lining of A. franciscana is endowed with numerous mesostructured inclusions that have not been previously reported. We hypothesize that their self-assembly was from proteinaceous polycrystalline units and carbohydrates. These mesostructured flakes displayed active optical properties, as an umbrella-like, reflective cover of the ovisac, which suggests a functional role in the reproduction of A. franciscana. In turn, studies into ovisac mesostructured inclusions could help to optimizing rearing Artemia as feed for fish farming. We propose Artemia ovisacs as an in vivo model system for studying mesostructure formation.

Combined proximal tubulopathy, crystal-storing histiocytosis, and cast nephropathy in a patient with light chain multiple myeloma

Background

The diagnosis of myeloma, a plasma dyscrasia, often results from the workup of unexplained renal disease. Persistent renal failure in myeloma is commonly caused by tubular nephropathy due to circulating immunoglobulins and free light chains. Myeloma cast nephropathy is characterized by crystalline precipitates of monoclonal light chains within distal tubules. Immunoglobulin crystallization rarely occurs intracellularly, within proximal tubular cells (light chain proximal tubulopathy) and interstitial histiocytes (crystal-storing histiocytosis). We present a case report of a rare simultaneous occurrence of light chain proximal tubulopathy, crystal-storing histiocytosis, and myeloma cast nephropathy in a patient with κ light chain multiple myeloma.

Case presentation

A 48-years-old man presented with uremia and anemia. Laboratory examination revealed low levels of serum IgG, IgA, and IgM. Serum and urine immunofixation electrophoresis showed a free κ monoclonal band. Bone marrow aspiration and biopsy revealed hypercellularity with marked plasmacytosis. Light microscopy revealed eosinophilic cuboid- and rhomboid-shaped crystals in the cytoplasm of proximal tubular epithelial cells, diffuse large mononuclear and multinuclear cells in the interstitium, and obstructed distal tubules with cast and giant cell reaction. Immunohistochemical examination indicated intense staining for κ light chains within casts, histiocytes, and tubular epithelial cells. Electron microscopy revealed electro-dense cuboid-, rhomboid-, or needle-shaped crystalline inclusions in proximal tubular epithelial cells and interstitial histiocytes. According to these results, we confirmed that this patient with myeloma exhibited simultaneous light chain proximal tubulopathy, crystal-storing histiocytosis, and myeloma cast nephropathy, which were attributed to monoclonal κ light chains. In addition to dialysis, the patient received induction chemotherapy with a combination of bortezomib, cyclophosphamide, and dexamethasone, followed by maintenance therapy with thalidomide. However, the patient did not regain renal function even when less than 5% plasma cells were detected in the bone marrow.

Conclusion

To the best of our knowledge, this is the first report of simultaneous light chain proximal tubulopathy, crystal-storing histiocytosis, and myeloma cast nephropathy in κ light chain multiple myeloma.

Crystalline podocytopathy and tubulopathy without overt glomerular proteinuria in a patient with multiple myeloma

Crystalline nephropathy is a rare yet well-known condition associated with multiple myeloma and other light chain–secreting disorders. Paraproteins that are resistant to proteolysis crystallize within proximal tubular cells and cause light-chain proximal tubulopathy, which presents clinically as Fanconi syndrome. Podocytes are rarely affected, and the crystalline inclusions within podocytes are typically precipitated, yielding significant glomerular proteinuria. Here we report a case of extensive crystalline inclusions primarily within podocytes and proximal tubules that presented only with Fanconi syndrome and renal insufficiency. Despite the presence of extensive crystalline inclusions in podocytes and diffuse foot process effacement, the patient had no clinical evidence suggestive of podocyte injury.

Spectrum of manifestations of monoclonal gammopathy-associated renal lesions

PURPOSE OF REVIEW

Monoclonal gammopathies result from an overt malignant process, such as multiple myeloma, or a premalignant process, such as monoclonal gammopathy of undetermined significance. The kidney is often affected in the setting of a monoclonal gammopathy. The term 'monoclonal gammopathy of renal significance (MGRS)' was recently introduced to draw attention to renal diseases related to the monoclonal gammopathy. In this review, we define the pathology of these monoclonal gammopathy-associated kidney diseases.

RECENT FINDINGS

Renal disease can be caused by deposition of the monoclonal immunoglobulin (direct mechanism) or by activation of the alternative pathway of complement by the monoclonal immunoglobulin (indirect mechanism). The deposition of monoclonal immunoglobulin can affect the glomeruli, tubules, and the interstitium and vessels. The glomerular diseases include proliferative glomerulonephritis with monoclonal immunoglobulin deposits, immunotactoid glomerulopathy, and, less commonly, fibrillary glomerulonephritis. Tubular lesions associated with monoclonal immunoglobulin include cast nephropathy and light-chain proximal tubulopathy. Lesions involving the glomeruli, tubules, interstitium or vessels include amyloidosis and monoclonal immunoglobulin deposition diseases. Rarely, monoclonal immunoglobulin may also cause C3 glomerulopathy or atypical hemolytic uremic syndrome by interfering with the regulation of the alternative pathway of complement.

SUMMARY

Monoclonal gammopathy are associated with a variety of kidney diseases. The monoclonal gammopathy-associated renal diseases are distinct in their pathogenesis, kidney biopsy findings, clinical presentation, progression, prognosis, and treatment. The term monoclonal gammopathy of renal significance helps highlight patients who have renal disease secondary to monoclonal immunoglobulin secreted by a premalignant or malignant clone, but is not a disease or diagnosis in itself.

Current anti-myeloma therapies in renal manifestations of monoclonal light chain-associated Fanconi syndrome: a retrospective series of 49 patients

We retrospectively reviewed 49 patients with light chain (LC) Fanconi syndrome (FS). Patients presented with chronic kidney disease (median estimated glomerular filtration rate (eGFR) of 33 ml/min/1.73 m²) and tubular proteinuria. All patients tested had elevated fractional excretion of phosphate, uric acid, generalized aminoaciduria and/or normoglycemic glycosuria. Thirty-eight patients had monoclonal gammopathy of renal significance and eleven patients had an overt hematological malignancy. The monoclonal LC isotype was kappa in 46/49 cases. Kidney biopsy in 39 patients showed various proximal tubular lesions and characteristic LC intracytoplasmic crystalline inclusions in 24 patients. Forty-two patients received chemotherapy. Patients with plasma cell proliferation (n=38) received bortezomib-based regimens (n=11), immunomodulatory agents (n=7) or alkylating agents (n=6). High-dose melphalan (HDM) followed by autologous stem cell transplantation was performed in 14 patients. Hematological response was obtained in 90% of evaluable patients, assessed on serum free light chains (FLC). GFR remained stable as long as hematological response was maintained and declined when serum FLC level rebounded. Improvement in proximal tubule function occurred in 13 patients. In patients with LC-associated FS, chemotherapy using HDM and/or new generation anti-myeloma agents can stabilize renal function and improve proximal tubule function. Serum FLC should be used to assess the hematological response, related to renal outcome.

Unique Renal Manifestation of Type I Cryoglobulinemia, With Massive Crystalloid Deposits in Glomerular Histiocytes, Podocytes, and Endothelial Cells

OBJECTIVES

We describe a 62-year-old woman with a 15-year history of a plasma cell dyscrasia (monoclonal IgGκ), manifested by type I cryoglobulinemia and dermal vasculitis.

METHODS

In addition to the clinical examinations, light microscopy with immunohistochemistry, sequential multicolor immunohistochemistry, and electron microscopy were used to characterize the crystalline deposits.

RESULTS

At initial presentation and for a later flare, she was treated with cyclophosphamide and prednisolone with good clinical response. She had renal function decline, microscopic hematuria, and proteinuria. A renal biopsy specimen revealed the presence of glomerular macrophages and duplication of the capillary walls with cellular interposition. Glomerular cells contained abundant needle-shaped eosinophilic crystalline inclusions positive for κ light chain. Electron microscopy confirmed the presence of intracytoplasmatic crystalline structures in endothelial cells, podocytes, and macrophages but not in the tubular epithelium. Rituximab treatment was started. At follow-up (now up to 6 months), renal function remained stable.

CONCLUSIONS

This patient displays a unique renal manifestation of type I cryoglobulinemia related to a plasma cell dyscrasia.

Histiocytic and Nonhistiocytic Glomerular Lesions: Foam Cells and Their Mimickers

Numerous histiocytes are sometimes noted in glomeruli, giving rise to a foamy-appearing glomerulus. Foamy-appearing glomeruli may also be noted in conditions that do not contain numerous histiocytes. These disease entities are rare, have different underlying causes and pathophysiology, and can cause a diagnostic dilemma. We have observed this histiocytic/foamy glomerular change on the kidney biopsy specimen in 5 different disease entities: crystal-storing histiocytosis, histiocytic glomerulopathy associated with macrophage-activating syndrome, thrombotic microangiopathy, lecithin-cholesterol acyltransferase deficiency, and lipoprotein glomerulopathy. We describe and compare the kidney biopsy findings of these histiocytic and foamy-appearing entities. It is important to recognize the kidney biopsy findings of these rare conditions to correctly evaluate and identify the cause and manage these patients.

Light Chain Proximal Tubulopathy: Clinical and Pathologic Characteristics in the Modern Treatment Era

Light chain proximal tubulopathy (LCPT) is characterized by cytoplasmic inclusions of monoclonal LC within proximal tubular cells. The significance of crystalline versus noncrystalline LCPT and the effect of modern therapies are unknown. We reported the clinical-pathologic features of 40 crystalline and six noncrystalline LCPT patients diagnosed between 2000 and 2014. All crystalline LCPTs were κ-restricted and displayed acute tubular injury. One-third of noncrystalline LCPT patients displayed λ-restriction or acute tubular injury. Only crystalline LCPT frequently required antigen retrieval to demonstrate monoclonal LC by immunofluorescence. In five of 38 patients, crystals were not detectable by light microscopy, but they were visible by electron microscopy. Hematolymphoid neoplasms, known before biopsy in only 15% of patients, included 21 monoclonal gammopathies of renal significance; 15 multiple myelomas; seven smoldering multiple myelomas; and three other neoplasms. Biopsy indications included Fanconi syndrome (38%; all with crystalline LCPT), renal insufficiency (83%), and proteinuria (98%). Follow-up was available for 30 (75%) patients with crystalline LCPT and all six patients with noncrystalline LCPT, of whom 11 underwent stem cell transplant, 16 received chemotherapy only, and nine were untreated. Complete or very good partial hematologic remissions occurred in six of 22 treated crystalline LCPT patients. By multivariable analysis, the only independent predictor of final eGFR was initial eGFR, highlighting the importance of early detection. All patients with crystalline LCPT treated with stem cell transplant had stable or improved kidney function, indicating the effectiveness of aggressive therapy in selected patients.

Pseudo-Peritoneal Carcinomatosis Presentation of a Crystal-Storing Histiocytosis With an Unmutated Monoclonal κ Light Chain

Crystal-storing histiocytosis (CSH) is a rare complication of monoclonal gammopathies caused by accumulation of crystalline material inside macrophages, and it may result in a variety of clinical manifestations depending on the involved organs. Although immunoglobulin κ light chains (LCs) seem to be the most frequent pathogenic component, very few molecular data are currently available.A 69-year-old man presented with a very poor performance status. Remarkable features were mesenteric lymph node enlargement and proteinuria, including a monoclonal κ LC. Light and electron microscopy studies revealed the presence of crystals within macrophages in the lymph nodes, bone marrow, and kidney, leading to the diagnosis of CSH. The pathogenic κ LC variable domain sequence was identical to the germline Vk3-2001/Jk201 gene segments, without any somatic mutation, suggesting an extra-follicular B cell proliferation.The patient was successfully treated with 4 cycles of bortezomib and dexamethasone. After a 12-month follow-up, he remains in hematological and renal remission.CSH may present as pseudo-peritoneal carcinomatosis and relate to a monoclonal κ LC encoded by an unmutated gene. Bortezomib-based therapy proved efficacious in this case.

The reduced expression of proximal tubular transporters in acquired Fanconi syndrome with κ light chain deposition

In a case of acquired Fanconi syndrome associated with smoldering myeloma, we confirmed the deposition of protease-resistant κ light chain proteins in a proximal tubular injury and found the decreased expression of apical tubular transporters including sodium glucose co-transporter, sodium phosphate co-transporter, uric acid transporter 1, and a decrease of Na(+)/K(+)-ATPase in the basolateral membrane. The protease-resistant kappa light chain has a pathological role in the expression of tubular transporters in the proximal tubule and causes Fanconi syndrome associated with smoldering myeloma.

Diagnosis of monoclonal gammopathy of renal significance

Monoclonal gammopathy of renal significance (MGRS) regroups all renal disorders caused by a monoclonal immunoglobulin (MIg) secreted by a nonmalignant B-cell clone. By definition, patients with MGRS do not meet the criteria for overt multiple myeloma/B-cell proliferation, and the hematologic disorder is generally consistent with monoclonal gammopathy of undetermined significance (MGUS). However, MGRS is associated with high morbidity due to the severity of renal and sometimes systemic lesions induced by the MIg. Early recognition is crucial, as suppression of MIg secretion by chemotherapy often improves outcomes. The spectrum of renal diseases in MGRS is wide, including old entities such as AL amyloidosis and newly described lesions, particularly proliferative glomerulonephritis with monoclonal Ig deposits and C3 glomerulopathy with monoclonal gammopathy. Kidney biopsy is indicated in most cases to determine the exact lesion associated with MGRS and evaluate its severity. Diagnosis requires integration of morphologic alterations by light microscopy, immunofluorescence (IF), electron microscopy, and in some cases by IF staining for Ig isotypes, immunoelectron microscopy, and proteomic analysis. Complete hematologic workup with serum and urine protein electrophoresis, immunofixation, and serum-free light-chain assay is required. This review addresses the pathologic and clinical features of MGRS lesions, indications of renal biopsy, and a proposed algorithm for the hematologic workup.

Crystalglobulin-induced nephropathy

Crystalline nephropathy refers to renal parenchymal deposition of crystals leading to kidney damage. The most common forms of crystalline nephropathy encountered in renal pathology are nephrocalcinosis and oxalate nephropathy. Less frequent types include urate nephropathy, cystinosis, dihydroxyadeninuria, and drug-induced crystalline nephropathy (e.g., caused by indinavir or triamterene). Monoclonal proteins can also deposit in the kidney as crystals and cause tissue damage. This occurs in conditions such as light chain proximal tubulopathy, crystal-storing histiocytosis, and crystalglobulinemia. The latter is a rare complication of multiple myeloma that results from crystallization of monoclonal proteins in the systemic vasculature, leading to vascular injury, thrombosis, and occlusion. In this report, we describe a case of crystalglobulin-induced nephropathy and discuss its pathophysiology and the differential diagnosis of paraprotein-induced crystalline nephropathy.

Crystalline nephropathies

CONTEXT

The kidney is a favored site for crystal deposition because of the high concentration of ions and molecules reached at the level of the renal tubules in the course of filtration. This review focuses on crystalline nephropathies in 4 broad categories: (1) dysproteinemia- associated, (2) drug-induced, (3) calcium-containing, and (4) metabolic or genetic.

OBJECTIVE

To provide a framework for accurate identification of the diverse types of crystals encountered in the kidney in order to formulate an appropriate differential diagnosis and guide additional testing and treatment.

DATA SOURCES

Review of pertinent published literature along with practical experience gained in a high-volume renal pathology laboratory.

CONCLUSIONS

Accurate identification of crystals encountered in the kidney is essential in detecting conditions ranging from hematologic malignancy to drug toxicity to metabolic disorders. Detailed clinical-pathologic correlation is needed to accurately diagnose the underlying cause of most crystalline nephropathies.

Crystal-storing histiocytosis: report of a case, review of the literature (80 cases) and a proposed classification

We report a case of crystal storing histiocytosis (CSH) of the upper lip and cheek in a 51-year-old woman and review the clinicopathologic features of 80 cases in the literature. These occurred in 41 men and 39 women with a respective mean age of 59 and 61 years (range 17-81 years). Forty-six patients (58%) had localized CSH, and, of these, 16 (35%) occurred in the head and neck, with the most common site being the eye/orbit. The remaining 34 patients (42%) had generalized CSH primarily involving bone marrow, liver, lymph nodes, spleen and/or kidney. Regardless of whether the CSH was localized or generalized, the vast majority of patients (90%) had an underlying lymphoproliferative or plasma cell disorder, especially multiple myeloma, lymphoplasmacytic lymphoma, or monoclonal gammopathy of undetermined significance. In 7 cases (8.8%), the CSH was associated with a variety of benign disorders, often with an inflammatory background, and no evidence of a clonal lymphoproliferative or plasma cell disorder. Treatment and prognosis varied according to the underlying disease. A classification of CSH based on etiology and/or associated disease and chemical composition of the crystal is proposed, rare non-immunoglobulin variants of CSH are discussed, and a differential diagnosis of other potentially confusing lesions is provided.

The morphologic spectrum and clinical significance of light chain proximal tubulopathy with and without crystal formation

The renal diseases most frequently associated with myeloma include amyloidosis, monoclonal immunoglobulin deposition disease, and cast nephropathy. Less frequently reported is light chain proximal tubulopathy, a disease characterized by κ-restricted crystal deposits in the proximal tubule cytoplasm. Light chain proximal tubulopathy without crystal deposition is only loosely related to the typical light chain proximal tubulopathy, and little is known about this entity. A search was performed of the 10 081 native kidney biopsy samples processed by our laboratory over the past 2 years for cases that had light chain restriction limited to the proximal tubule cytoplasm. A total of 10 cases of light chain proximal tubulopathy without crystal deposition were found representing 3.1% of light chain-related diseases. Nine of these 10 showed λ-light chain restriction. Only three cases of light chain proximal tubulopathy with crystals were found accounting for 0.9% of light chain-related diseases. Two of these three were κ subtype. Plasma cell dyscrasia was unsuspected in seven of the 10 patients with light chain proximal tubulopathy without crystals at the time of renal biopsy. After the biopsy was reported, follow-up was available on 9/10 patients with 9/9 showing a plasma cell dyscrasia including 8/9 with multiple myeloma. We found that light chain proximal tubulopathy without crystal formation, despite being rarely described in the literature, is over three times more common than light chain proximal tubulopathy with crystal formation in our series. And given that it is often associated with previously unrecognized myeloma, it is a critically important diagnosis.

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.