C3 Glomerulopathy is a rare form of kidney disease due to dysregulation of the alternative complement pathway. We report a case of a college-aged woman with C3 glomerulonephritis (C3GN), presenting with the unexpected extrarenal manifestation of pulmonary hemorrhage. The patient presented with a nephritic urinary sediment and acute kidney injury after a recent infection. Kidney biopsy demonstrated focal endocapillary proliferative, crescentic, and necrotizing glomerulonephritis with bright glomerular C3 staining only. Electron microscopy revealed mesangial, intramembranous, and subendothelial deposits. After 2 doses of intravenous methylprednisolone, the patient developed spontaneous hemoptysis and respiratory compromise requiring emergent intubation. Bronchoscopy and computed tomography findings were consistent with diffuse alveolar hemorrhage. Notable laboratory results included C3, 40 (reference range, 75-175) mg/dL, and negative antinuclear antibody, antineutrophil cytoplasmic antibody, and anti-glomerular basement membrane serology results. As an outpatient, genetic testing revealed the presence of C3 glomerulopathy risk alleles. A diagnosis of C3GN complicated by pulmonary hemorrhage was made. There was initial response to treatment with steroids and mycophenolate mofetil; however, after repeated relapses of proteinuria and hematuria, treatment with eculizumab showed an initial response, but the patient subsequently became hemodialysis dependent. Our case highlights that C3GN can present with crescents and have other extrarenal manifestations such as pulmonary hemorrhage and should also be considered part of the differential diagnosis in patients presenting with pulmonary renal syndrome. (C) 2019 The Author(s). Published by Elsevier Ina on behalf of National Kidney Foundation, Inc.

Introduction: Fibrillary glomerulonephritis (FGN) is a rare disease with unknown pathogenesis and a poor prognosis. Until now, the diagnosis of this disease has required demonstration of glomerular deposition of randomly oriented fibrils by electron microscopy that are Congo red negative and stain with antisera to Igs. We recently discovered a novel proteomic tissue biomarker for FGN, namely, DNAJB9. Methods: In this work, we developed DNAJB9 immunohistochemistry and tested its sensitivity and specificity for the diagnosis of FGN. This testing was performed on renal biopsy samples from patients with FGN (n = 84), amyloidosis (n = 21), a wide variety of non- FGN glomerular diseases (n = 98), and healthy subjects (n = 11). We also performed immunoelectron microscopy to determine whether DNAJB9 is localized to FGN fibrils. Results: Strong, homogeneous, smudgy DNAJB9 staining of glomerular deposits was seen in all but 2 cases of FGN. The 2 cases that did not stain for DNAJB9 were unique, as they had glomerular staining for IgG only (without kappa or lambda) on immunofluorescence. DNAJB9 staining was not observed in cases of amyloidosis, in healthy subjects, or in non-FGN glomerular diseases (with the exception of very focal staining in 1 case of smoking- related glomerulopathy), indicating 98% sensitivity and > 99% specificity. Immunoelectron microscopy showed localization of DNAJB9 to FGN fibrils but not to amyloid fibrils or immunotactoid glomerulopathy microtubules. Conclusion: DNAJB9 immunohistochemistry is sensitive and specific for FGN. Incorporation of this novel immunohistochemical biomarker into clinical practice will now allow more rapid and accurate diagnosis of this disease.

BACKGROUND AND OBJECTIVES:Kidney involvement in Waldenström macroglobulinemia is less well described compared with kidney manifestations in multiple myeloma. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS:Of the 1363 patients seen with Waldenström macroglobulinemia and other IgM-secreting B cell lymphoproliferative disorders seen at the Mayo Clinic between 1996 and 2015, 57 kidney biopsies were retrospectively studied. The biopsy findings were correlated with clinical, kidney, and hematologic characteristics. Criteria for inclusion were evidence of a monoclonal IgM protein and availability of a kidney and a bone marrow biopsy for review. Glomerular and tubulointerstitial pathologies were categorized according to whether they were related to the monoclonal IgM. RESULTS:Of the 57 patients identified, monoclonal gammopathy-related kidney lesions were identified in 82% (47 of 57 biopsies), whereas nonmonoclonal gammopathy-related kidney lesions were seen in 18% (ten of 57). Monoclonal gammopathy-related kidney lesions included monoclonal Ig-related amyloidosis (n=19; 33%), nonamyloid glomerulopathy (n=20, 35%), and tubulointerstitial nephropathies (n=8; 14%). The most common monoclonal gammopathy-related kidney lesion was monoclonal Ig-related amyloidosis (n=19; 33%) followed by cryoglobulinemic GN (n=13; 28%). Lymphoma infiltration was the most common tubulointerstitial lesion (n=4; 9%). The hematologic diagnosis was Waldenström macroglobulinemia in 74% (n=42), monoclonal gammopathy of renal significance in 16% (n=9), and marginal zone lymphoma (n=2), chronic lymphocytic leukemia (n=2), and low-grade B cell lymphoma (n=2) in 4% each. CONCLUSIONS:Our study confirms a diverse variety of kidney lesions in patients with monoclonal IgM gammopathy.

BACKGROUND:Complement activation plays an important role in the pathophysiology of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), although it remains unclear which pathway is activated. Whether pauci-immune necrotizing crescentic glomerulonephritis (pauci-immune GN) with negative ANCA serology is part of the spectrum of AAV or a different disease entity is essentially unknown.METHODS:We used proteomic analysis to delineate the complement profile in a series of 13 kidney biopsies of patients with pauci-immune GN, with either proteinase 3 (PR3) (five patients) or myeloperoxidase (MPO) antibodies (four patients) or with consistently negative ANCA serology (four patients). Immunofluorescence staining of glomeruli was essentially negative in the PR3-ANCA and MPO-ANCA groups, while a mild staining for C3 was seen in the ANCA-negative cases. No electron-dense deposits were found in the PR3-ANCA and MPO-ANCA groups, but mesangial and few subepithelial deposits were clearly present in the ANCA-negative specimens.RESULTS:Mass spectrometry revealed low spectra numbers for C3 and immunoglobulins in both PR3-positive and MPO-positive patients with minimal or no C4 and C9. In contrast, larger spectra numbers for C3, moderate spectra numbers for C9, complement factor H-related protein-1 and low spectra numbers for C4, C5 and immunoglobulins were found in the ANCA-negative cases.CONCLUSION:While complement activation is noted in AAV, the complement activation appears to be more prominent in the ANCA-negative glomerulonephritis. The larger amount of C3 and moderate amount of C9 in the ANCA-negative glomerulonephritis implies activation of the alternate and terminal pathway of complement, suggesting that this entity may be caused or promoted by a genetic or acquired defect in the alternative pathway.

Objectives: To describe the change in the incidence rates of primary and secondary focal segmental glomerulosclerosis (FSGS) from 1994 through 2013 in Olmsted County, Minnesota, and to identify the clinical and biopsy characteristics that distinguish primary from secondary FSGS. Patients and Methods: Olmsted County adult residents with native kidney biopsy from January 1, 1994, through December 31, 2013, and FSGS as the only glomerulopathy were identified. The clinical and pathologic characterstics of primary and secondary FSGS were described and compared, and incidence rates were calculated. Results: Of 370 adults biopsied, 281 had glomerular diseases, of which 46 (16%) had FSGS. From 19942003 to 2004-2013, there were significant increases in kidney biopsy rates (14.7 [95% CI, 12.1-17.3] vs 22.9 [95% CI, 20.0-25.7] per 100,000 person-years, 17% increase per 5 years; P<.001) and total FSGS rates (1.4 [95% CI, 0.6-2.2] vs 3.2 [95% CI, 2.1-4.3] per 100,000 person-years, 41% increase per 5 years; P = .02). Compared with patients with limited foot process effacement (<80%), patients with diffuse effacement (>= 80%) without an identifiable cause had lower serum albumin levels (P<.001), had higher proteinuria (P<.001), and were more likely to have nephrotic syndrome (100% vs 4%; P<.001). Patients with diffuse effacement without an identifiable cause were classified as primary FSGS, which accounted for 3 of 12 patients (25%) during 1994-2003 and 9 of 34 (26%) during 2004-2013. Conclusion: Although the incidence of FSGS has increased, the proportions of primary and secondary FSGS have remained stable. (C) 2017 Mayo Foundation for Medical Education and Research

Background: C3 glomerulopathy (C3G) is caused by overactivity of the alternative pathway of complement that results in bright glomerular C3 staining with minimal or no deposition of immunoglobulins on immunofluorescence microscopy. Laser microdissection and mass spectrometry of the two subtypes, C3 glomerulonephritis (C3GN) and dense deposit disease (DDD), have identified C3 as the predominant glomerular complement protein, although lesser amounts of C9, C5, C6, C7 and C8 are detectable. C3 plays a central role in complement activity, with its proteolytic cleavage first generating C3a and C3b, followed by inactivation of C3b generating iC3b (which includes C3&agr; and C3&bgr;), which undergoes further breakdown yielding C3c and terminal breakdown fragment C3dg. The composition of C3 breakdown products in C3G is not known. Methods: In this study, we chose six cases each of C3GN and DDD to analyze the composition of C3 deposits. We analyzed the amino acid sequence of C3 spectra detected by mass spectrometry to determine the relative abundance of C3 fragments in C3G. Thus we were able to determine the amino acid sequences mapping to the various C3 activation products including C3dg, C3&agr; (C3&agr;1 and &agr;2), and C3&bgr; that are part of C3b/iC3b/C3c. Results: C3dg is the predominant cleavage product detected with the highest amino acid coverage. The remaining amino acids map to C3&agr; (C3&agr;1 and &agr;2) and C3&bgr;. Amino acids mapping to C3a and C3f are absent. Taken together, the C3&agr; and C3&bgr; amino acids represent iC3b prior to or after C3c cleavage of C3dg. The C3 spectra for both C3GN and DDD are surprisingly similar. Conclusion: The finding of large amounts of C3dg suggests that C3b deposition in the glomerulus is an active process triggered by thioester binding of C3b to the glycocalyx overlying the glomerular endothelial cells and glomerular basement membrane. Regulatory protein‐mediated inactivation of C3b results in the generation of iC3b. After additional cleavages, mostly C3dg remains.

Introduction: Steroid-resistant focal segmental glomerulosclerosis (SR-FSGS) is a common glomerulopathy associated with nephrotic range proteinuria. Treatment goals are reduction in proteinuria, which can delay end-stage renal disease.Methods: Patients with SR-FSGS were enrolled in a randomized, double-blind placebo-controlled trial of fresolimumab, a monoclonal anti-transforming growth factor-beta antibody, at 1 mg/kg or 4 mg/kg for 112 days, followed double-blind for 252 days (NCT01665391). The primary efficacy endpoint was the percentage of patients achieving partial (50% reduction) or complete (<300 mg/g Cr) remission of proteinuria.Results: Of 36 enrolled patients, 10, 14, and 12 patients received placebo, fresolimumab 1 mg/kg, and fresolimumab 4 mg/kg, respectively. The baseline estimated glomerular filtration rate (eGFR) and urinary protein/creatinine ratio were 63 ml/min/1.73 m(2) and 6190 mg/g, respectively. The study was closed before reaching its target of 88 randomized patients. None of the prespecified efficacy endpoints for proteinuria reduction were achieved; however, at day 112, the mean percent change in urinary protein/creatinine ratio (a secondary efficacy endpoint) was -18.5% (P = 0.008), +10.5% (P = 0.52), and +9.0% (P = 0.91) in patients treated with fresolimumab 1 mg/kg, fresolimumab 4 mg/kg, and placebo, respectively. There was a nonsignificant trend toward greater estimated glomerular filtration rate decline in the placebo group compared to either of the fresolimumab-treated arms up to day 252.Discussion: The study was underpowered and did not meet the primary or secondary endpoints. However, fresolimumab was well tolerated and is appropriate for continued evaluation in larger studies with adequate power.

There is currently no standard treatment for monoclonal immunoglobulin (MIg)-associated C3 glomerulopathy, and treatment is often dictated by the extent of the monoclonal gammopathy. Although chemotherapy treatment for MIg-associated C3 glomerulopathy may stabilize renal function, the overall renal prognosis of MIg-associated C3 glomerulopathy is still poor with frequent progression to end-stage renal disease. We present a case of a 55-year-old man with IgG-κ gammopathy-associated C3 glomerulonephritis (C3GN) with bone marrow biopsy demonstrating 5 - 10 κ-restricted plasma cells. Following chemotherapy treatment unfortunately, the patient encountered relapsing courses of the disease. The patient subsequently received high-dose melphalan treatment followed by autologous hematopoietic stem cell transplant (ASCT). At 8 months follow-up, the patient remained hematologic response with stable kidney function. Since ASCT can offer durable hematologic remission, ASCT can potentially be a curative treatment option for patients with MIg-associated C3GN.
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In both atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G) complement plays a primary role in disease pathogenesis. Herein we report the outcome of a 2015 Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference where key issues in the management of these 2 diseases were considered by a global panel of experts. Areas addressed included renal pathology, clinical phenotype and assessment, genetic drivers of disease, acquired drivers of disease, and treatment strategies. In order to help guide clinicians who are caring for such patients, recommendations for best treatment strategies were discussed at length, providing the evidence base underpinning current treatment options. Knowledge gaps were identified and a prioritized research agenda was proposed to resolve outstanding controversial issues.

Focal segmental glomerulosclerosis (FSGS) is a lesion and not a disease. This conundrum is the crux of controversies regarding interventions to alter its natural history. In the broadest sense, the lesion can be primary (idiopathic), or secondary to a process originating outside the kidneys or to a genetic mutation. The organ-based target is the podocyte, and the mechanisms re-sponsible for the podocytopathy are numerous and diverse. Recurrence of primary FSGS in renal allografts provides the best evidence for the existence of a circulating factor or factors, the nature of which remains uncertain. The separation of primary from secondary FSGS clinically and pathologically is challen-ging, but full-blown nephrotic syndrome and diffuse (univer-sal) foot process effacement are strong signals for a primary form of FSGS. It is imperative that clinical trials designed to in-vestigate therapeutic strategies for patients with a lesion of FSGS pay careful attention to the separation of primary from secondary forms of FSGS. This critical review provides a rationale and a process for helping to ensure that this is accomplished, such that clinical trials provide useful information and treatment re-sponsiveness applicable to the primary forms of FSGS.

Rituximab is an anti-CD20 monoclonal antibody frequently used for the treatment of non-Hodgkin's lymphoma, chronic lymphocytic leukemia (CLL), rheumatoid arthritis (RA), and anti-neutrophilic cytoplasmic antibody (ANCA)-associated vasculitis. In addition, rituximab has recently been increasingly used as an off-label treatment in a number of inflammatory and systemic autoimmune diseases. It is advised that rituximab infusion may cause infusion reactions and adverse cardiac effects including arrhythmia and angina, especially in patients with prior history of cardiovascular diseases. However, its detailed cardiotoxicity profile and effects on cardiac function were not well described. We report a 51-year-old man who developed non-ischemic cardiomyopathy after rituximab treatment for membranous nephropathy. The patient experienced reduced cardiac functions within 48 hours after the initial infusion, which remained markedly reduced at 9-month follow-up. As the utility of rituximab expands, physicians must be aware of this serious cardiovascular adverse effect.

ObjectiveS100A8/A9 (calprotectin) has shown promise as a biomarker for predicting relapse in antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis (AAV). This study was undertaken to investigate serum S100A8/A9 level as a biomarker for predicting future relapse in a large cohort of patients with severe AAV.MethodsSerum levels of S100A8/A9 were measured at baseline and months 1, 2, and 6 following treatment initiation in 144 patients in the Rituximab in ANCA‐Associated Vasculitis trial (cyclophosphamide/azathioprine versus rituximab [RTX] for induction of remission) in whom complete remission was attained.ResultsPatients were divided into 4 groups: proteinase 3 (PR3)–ANCA with relapse (n = 37), PR3‐ANCA without relapse (n = 56), myeloperoxidase (MPO)–ANCA with relapse (n = 6), and MPO‐ANCA without relapse (n = 45). Serum S100A8/A9 level decreased in all groups during the first 6 months of treatment. The percentage reduction from baseline to month 2 was significantly different between patients who experienced a relapse and those who did not in the PR3‐ANCA group (P = 0.046). A significantly higher risk of relapse was associated with an increase in S100A8/A9 level between baseline and month 2 (P = 0.0043) and baseline and month 6 (P = 0.0029). Subgroup analysis demonstrated that patients treated with RTX who had increased levels of S100A8/A9 were at greatest risk of future relapse (P = 0.028).ConclusionAn increase in serum S100A8/A9 level by month 2 or 6 compared to baseline identifies a subgroup of PR3‐ANCA patients treated with RTX who are at higher risk of relapse by 18 months. Since RTX is increasingly used for remission induction in PR3‐ANCA–positive patients experiencing a relapse, S100A8/A9 level may assist in identifying those patients requiring more intensive or prolonged treatment.

Background Membranous nephropathy (MN) can recur in kidney allografts leading to graft dysfunction and failure. The aims of these analyses were to assess MN recurrence, clinical and histologic progression, and response to anti-CD20 therapy. Methods Included were 63 kidney allograft recipients with biopsy proven primary MN followed up for 77.0 (39-113) months (median, interquartile range). Disease recurrence was diagnosed by biopsy (protocol or clinical), and follow-up was monitored by laboratory parameters and protocol biopsies. Results Thirty of 63 patients (48%) had histologic recurrence often during the first year. In 53% of the cases, recurrence was diagnosed by protocol biopsy. Recurrence risk was higher in patients with higher proteinuria pretransplant [hazard ratio = 1.869 (95% confidence interval, 1.164-3.001) per gram, P = 0.010] and those with anti-phospholipase A2 receptor antibodies [hazard ratio = 3.761 (1.635-8.652), P = 0.002]. Thirteen patients with recurrence had no clinical progression, and in 2, MN resolved histologically. Seventeen of 63 patients (27%) had progressive proteinuria and were treated with anti-CD20 antibodies, resulting in complete response in 9 (53%), partial response in 5 (29%), and no response in 3 (18%). Posttreatment biopsies were obtained in 15 patients and showed histologic resolution in 6 (40%). Disease recurrence did not correlate with graft survival. However, 5 of 11 (45.4%) graft losses were due to recurrent MN. Death-censored graft survival in MN did not differ from that of 273 control recipients with autosomal dominant polycystic kidney disease. Conclusions Membranous nephropathy recurs in 48% of cases threatening the allograft. Treatment of early but progressive recurrence with anti-CD20 antibodies is quite effective achieving clinical remission and histologic resolution of MN.

Thrombotic microangiopathies (TMAs) comprise a heterogeneous set of conditions linked by a common histopathologic finding of endothelial damage resulting in microvascular thromboses and potentially serious complications. The typical clinical presentation is microangiopathic hemolytic anemia accompanied by thrombocytopenia with varying degrees of organ ischemia. The differential diagnoses are generally broad, while the workup is frequently complex and can be confusing. This statement represents the joint recommendations from a multidisciplinary team of Mayo Clinic physicians specializing in the management of TMA. It comprises a series of evidence- and consensus-based clinical pathways developed to allow a uniform approach to the spectrum of care including when to suspect TMA, what differential diagnoses to consider, which diagnostic tests to order, and how to provide initial empiric therapy, as well as some guidance on subsequent management.

Kidney diseases resulting from abnormal control of the complement alternative pathway include atypical hemolytic uremic syndrome, C3 glomerulonephritis, and dense-deposit disease, as well as atypical postinfectious glomerulonephritis. Although clinically diverse, they all result from loss of surface or fluid-phase complement control, caused by acquired or genetic defects in the complement alternative pathway. As such, the diagnostic approach is similar and includes a comprehensive biochemical, genetic, and pathologic analysis of the complement pathway. The biochemical test battery includes functional activity measurements of the entire complement pathway, functional and quantitative analysis of individual components and regulators, and quantification of activation products. In patients with a thrombotic microangiopathy, ADAMTS-13 activity should be determined to exclude a thrombotic thrombocytopenic purpura. The spectrum of genes currently known to be involved in the pathogenesis of alternative pathway disorders is rapidly expanding. Pathologic analysis of a kidney biopsy specimen is sophisticated with ad hoc immunofluorescence studies and laser microdissection with mass spectrometry. The identification of the underlying defect in the alternative pathway based on this comprehensive analysis will allow treatment to be directed to the site of dysregulation.

Recent reports suggest that deep hematologic responses to chemotherapy are associated with improved renal outcomes in monoclonal immunoglobulin deposition disease (MIDD). Here we describe the long term outcomes and identify prognostic factors after first line treatment of the largest reported series of patients with MIDD. Between March 1992 and December 2014, 88 patients with MIDD were seen at Mayo Clinic, MN. Renal responses were defined using criteria used for light chain amyloidosis (AL) or those used by the IMWG. Sixty-one (69%) patients had a GFR < 30 mL/min/1.73 m2 and 16 (18%) were on renal replacement therapy at diagnosis. The interval between albuminuria or elevation in creatinine and MIDD diagnosis was 12 months suggesting a delay in diagnosis. Thirty-seven patients (42%) had at least a hematologic CR/VGPR. Fifty-three (60%) received an autologous stem cell transplant (ASCT) or proteasome inhibitor (PI)-based treatments. Patients receiving ASCT or PI-based therapies were more likely to achieve at least a hematologic CR/VGPR compared to those receiving other therapies: 66% vs 2%, p < 0.0001. Patients that achieved a hematologic CR were more likely to achieve a renal response (53% vs 24%, p = 0.001). Five year overall and renal survival for the entire cohort was 67% and 57%, respectively. In multivariate analyses, a baseline GFR < 20 mL/min/1.73 m2 and a renal response (using AL or IMWG criteria) were independently predictive of progression to dialysis. This study confirms that deep hematologic responses, best achieved with ASCT or PI-based therapies, are a prerequisite to achieving renal responses. Am. J. Hematol. 91:1123-1128, 2016. © 2016 Wiley Periodicals, Inc.

We describe a rare case of light chain proximal tubulopathy developing in a kidney transplant 12 months following transplantation. The patient was known to have a monoclonal gammopathy of undetermined significance (MGUS) for more than 15 years. A kidney biopsy done to determine the cause of decline in kidney transplant function showed light chain proximal tubulopathy characterized by numerous eosinophilic and fuchsinophilic granules in proximal tubular epithelial cells, which stained for κ light chains on pronase-based immunofluorescence studies. Electron microscopy confirmed the diagnosis and showed numerous amorphous and geometrically shaped inclusions in proximal tubular epithelial cells. Evaluation of free light chains revealed markedly elevated κ light chains and bone marrow biopsy showed 5% to 10% κ light chain-restricted plasma cells. Retrospective evaluation of the native kidney biopsy performed 15 years earlier also showed numerous fuchsinophilic granules in proximal tubules that stained brightly for κ light chains on pronase-based immunofluorescence studies. The patient was treated with a regimen of bortezomib and dexamethasone with good partial hematologic response and improvement of kidney function. To summarize, we describe a case of recurrent light chain proximal tubulopathy in the transplant, which is an unusual but important cause of decreased kidney function in the setting of a monoclonal gammopathy.

Apolipoprotein A-IV associated amyloidosis (AApoAIV amyloidosis) is a rare cause of amyloidosis with only a single reported case. Here we describe the clinical, biopsy, and mass spectrometry characteristics of 11 cases of renal AApoAIV amyloidosis encompassing 9 men and 2 women with a mean age at diagnosis of 63.5 years. Progressive chronic kidney disease (mean serum creatinine 2.9 mg/dl) was the most common cause for biopsy with proteinuria absent or minimal in all except one. Hematological and serological evaluation was negative in 9 patients, while 2 had a monoclonal gammopathy. The renal biopsy findings were striking and showed large amounts of eosinophilic Congo-red positive amyloid deposits restricted to the renal medulla with sparing of the renal cortex. In 6 cases, peritubular amyloid was noted in addition to the interstitial involvement. Immunofluorescence studies were negative for immunoglobulins. Electron microscopy showed nonbranching fibrils measuring 7 to 10 nm in diameter. Laser microdissection of the amyloid deposits followed by mass spectrometry showed large spectra number (a semiquantitative measure of abundance) for AApoAIV protein ranging from 49 to 169 (average 85), serum amyloid protein (average 19), and apolipoprotein E (average 48). Importantly, no peptides were detected for any other forms of known amyloidogenic precursor proteins. Thus, renal AApoAIV amyloidosis typically presents with progressive chronic kidney disease and histologically exhibits extensive medullary involvement with sparing of the cortex. The diagnosis is best established by mass spectrometry. Hence, a high degree of suspicion and examination of the renal medulla is required to make the diagnosis.