Section 5 -

Contributions of Electron Microscopy to the Diagnosis of Plasma Cell Dyscrasia-Associated Renal Lesions Guillermo A. Herrera Saint Louis University School of Medicine St. Louis, Missouri

Electron microscopy (EM) plays a unique role in the diagnosis of plasma cell dyscrasia (PCD)-associated renal pathology. Much of the morphologic knowledge that has been acquired in these diseases predominantly in the last three decades has been possible because of the key role that EM has played. Not only for diagnostic purposes but also in research applications, EM has been a fundamental technique that has provided an added dimension to the understanding to these disorders. Although light (LM) and immunofluorescence (IF) microscopy have been very useful in helping to characterize the morphological spectrum of renal manifestations associated with PCDs, a significant percentage of the cases require EM evaluation for substantiating the diagnosis, and in a smaller number of the cases ultrastructural evaluation is absolutely essential to make the diagnosis. The role that immunoelectron microscopy (IEM) has played in the evaluation of these disorders is also noteworthy. The unusual, early and subtle manifestations may be entirely missed using LM, IF and routine EM, or the findings may not be definitive enough to establish an unequivocal diagnosis. It is in these instances that IEM can be crucial. Unfortunately, IEM is not widely used and only a few laboratories utilize it and are proficient at it. IEM is rather simple and requires no special expertise. As is the case with all techniques, initial instruction and practice are necessary for accurate and reproducible results to be obtained. Throughout the years, EM has been recognized as an important technique to identify amyloid and light and heavy chain deposits in all renal compartments, to the point where it is arguably the most useful diagnostic technique in those cases where questions arise as to the correct diagnosis, as it provides clear and distinct morphologic findings that permit unequivocal diagnoses. Not only EM and IEM are important in the assessment of glomerular pathology in PCD-related disorders but also they are also crucial techniques in the characterization of interstitial and vascular manifestations which unfortunately are often completely ignored. While the specific role of EM in the diagnosis of light chain (myeloma) cast nephropathy is still being defined, EM is of much more documented value in the evaluation of other types of tubular interstitial and vascular pathology associated with PCDs. The casts in light chain cast nephropathy can be quite varied in their ultrastructural appearance and usually, but not always, found in the distal nephrons. In some instances, they are composed of non-descript proteinaceous material and in a minority of the cases they may exhibit crystallized light chains. These casts may also be fibrillary or may contain markedly electron dense material with well defined fracture planes easily identifiable ultrastructurally. EIM may define monoclonality when IF is unable to do so. The lesions seen in the proximal tubules are also heterogeneous. Acute tubular damage associated with an activated lysosomal system with atypical lysosomes is the most common pattern of proximal tubular damage that can be seen in these cases. Another very characteristic lesion that can be seen in proximal tubules is characterized by the presence of intracytoplasmic kappa-positive crystalline-like or fibrillary inclusions. This pattern is typically noted in renal Fanconi syndrome with the patients exhibiting glycosuria, aminoaciduria and phosphaturia. An important fact that has not been well publicized is that not all light/heavy chain deposits are recognized by the antibodies to kappa and lambda light or heavy chains used in the diagnostic IF battery of stains applied routinely to renal specimens. The light and heavy chains can be so structurally abnormal that certain epitopes may be missing, resulting in lack of detection by IF. In other cases, non specific staining may result in the inability to establish monoclonality and thus confirming or determining a precise diagnosis. In these cases, EM and/or IEM become absolutely essential to establish a final diagnosis or rule out the presence of a PCD-associated disorder. As a result of the recognition of the value of EM in the diagnosis of these lesions, renal manifestations of PCDs are now depicted more often and earlier in renal biopsies. This presentation will address the immuno-morphologic correlates of the various renal lesions seen in PCD and will emphasize the importance of EM in the accurate diagnosis of these conditions. The use of EM in the diagnosis of PCD-related renal lesions permits more accurate characterization of these lesions and in some cases it is essential to be able to make the diagnosis. In selected cases, there is a need to go to the next diagnostic level-IEM- to obtain an accurate and undisputable diagnosis. At the end of the presentation the audience will have a clear understanding of the role that EM plays in the evaluation of PCD-related renal lesions. It is imperative to recognize that morphologic expressions in these disorders are very heterogeneous and that LM and IF may not provide definitive diagnostic information. These facts underscore the importance of correlating data obtained from all diagnostic techniques and the use of advanced diagnostic techniques (such as IEM) at least in selected cases when the data obtained from clinical and laboratory sources as well as from all routine diagnostic techniques remains unclear or controversial. References: Herrera, GA: The contributions of electron microscopy to the understanding and diagnosis of plasma cell dyscrasia-related renal lesions. Med. Electron Microsc. 34:1-18, 2001. Sanders, PW, Herrera, GA, Lott, RL, Galla, JH: Morphologic alterations of the proximal tubules in light chain-related renal diseases. Kidney Int. 33: 881-889, 1988. Truong, LD, Mawad, J, Cagle, P et al: Cytoplasmic crystals in multiple myeloma-associated Fanconi's syndrome. Arch. Pathol. Lab. Med. 113: 781-785,1989. Sanders, PW, Herrera, GA: Monoclonal immunoglobulin light chain-related renal diseases. Semin. Nephrol. 13:324-341, 1993. Herrera, GA: Renal manifestations of plasma cell dyscrasias: an appraisal from the patients' bedside to the research laboratory. Ann. Diagn. Pathol. 4:174-200, 2000. Kambham, N, Markowitz, GS, Appel, GB et al: Heavy chain deposition disease: the disease spectrum. Am. J. Kidney Dis. 33:954-963, 1999. Lajoie, G, Leung, R, Bargman, JM: Clinical, biochemical and pathological features in a patient with plasma cell dyscrasia and Fanconi syndrome. Ultrastruct. Pathol. 24:221-226, 2000. Isaac, J, Herrera, GA: Renal biopsy as a primary diagnostic tool in plasma cell dyscrasias. Pathol. Case Rev. 3:183-189, 1998. Novak, L, Cook, WJ, Herrera, GA, Sanders, PW: AL-amyloidosis is underdiagnosed in renal biopsies. Nephrol. Dial. Transplant. 19: 3050-3053, 2004. Uribe-Uribe N, Herrera, GA: Ultrastructure of tubular casts. Ultrastruct. Pathol. 30:159-166, 2006. Lin, J, Markowitz, GS, Valeri, AM et al: Renal monoclonal immunoglobulin deposition disease: the disease spectrum. J. Am. Soc. Nephrol. 12:1482-1492, 2001. Markowitz, GS: Dysproteinemias and the kidney. Adv. Anat. Pathol. 11:49-63, 2004. Herrera, GA, Sanders, PW, Reddy, V et al: Ultrastructural immunolabeling: A unique diagnostic tool in monoclonal light chain related renal disorders. Ultrastruct. Pathol. 17:93-113, 1993. Kapadia, SB: Multiple myeloma: a clinicopathologic study of 62 consecutive autopsied cases. Medicine (Baltim) 39: 380-392, 1080. Kyle, RA: Multiple myeloma. Review of 869 cases. Mayo Clin. Proc. 50: 29-40, 1975. Sanders, PW, Booker, BB: Pathophysiology of cast nephropathy from human Bence Jones proteins. J. Clin. Invest. 89: 630-639, 1992.