CORRESPONDENCE
IMMUNOTACTOID GLOMERULOPATHY
is learned of its origin. Until then , in our opinion, the "splitters" among taxonomists do not offer any advantage over the "Iumpers," as there is no practical value to a proliferation of diagnostic terms based on ultrastructural variances of no known significance. In the meantime, while we learn more of this unusual glomerular deposit, the cause of glomerular taxonomy is not served by those who misuse an othelWise useful term in an effort to apply their own. The literature about this lesion is now growing in an informative manner. This alone provides a barometer for the value of the recognition and labeling of the lesion known as immunotactoid g1omerulopathy. Edmund J. Lewis, MD Stephen M. Korbel, MD Melvin M . Schwartz, MD Rush Medical College Chicago,IL
To the Editor: It is true that in nephrology, as in all scientific endeavors, it is the burden of the taxonomist to develop useful systems of classification. These systems serve to clarify the similarity or identity of certain characteristics among individuals or groups of individuals. Hence the categorization of renal pathology according to established morphological criteria plays an important role in our perceptions about disease processes and ways in which they may be studied and treated. The purpose of taxonomy is therefore one of clarification. It is unfortunate that we occasionally fail and an erroneous classification may only serve to confuse the situation. The article by Alpers l entitled "Immunotactoid (Microtubular) glomerulopathy: An entity distinct from fibrillary glomerulonephritis?" is a regrettable example of the latter. The term "immunotactoid g1omerulopathy (ITG)" was coined in order to introduce the lesion to the nephrology community in unambiguous terms.2 Other descriptions such as " congo-red negative amyloid"3 and " fibrillary glomerulonephritis,'" which emphasize the ultrastructural appearance of the deposits while ignoring their immunoglobulin content, seemed less able to communicate the unique nature of this clinicopathological entity. Hence, nephrologists and pathologists were alerted to (I) the existence of this unusual glomerulopathy; (2) the need for a thorough evaluation to rule out other systemic diseases associated with organized deposits composed of immunoglobulin, such as cryoglobulinemia (which is illustrated in the case presented by Dr Alpers), paraproteinemias (demonstrated in much of the literature selected by Dr Alpers to support his argument), and systemic lupus erythematosus; (3) distinguish this lesion from amyloid, a lesion for which it had previously been mistaken, and (4) the clinical course experienced by patients with this clinicopathological entity before and after renal transplantation. 5• 7 Because subtle differences in the morphology and size of the organized material in ITG are of unknown clinical significance, we must reserve judgement until something more
I. Alpers CE: Immunotactoid (microtubular) g1omerulopathy: An entity distinct from fibrillary glomerulonephritis? Am J Kidney Dis 19:185-191 , 1992 2. Schwartz MM, Lewis EJ: The quarterly case: Nephrotic syndrome in a middle-aged man. Ultrastruct Pathol 1:575582, 1980 3. Rosenmann E, Eliakim M: Nephrotic syndrome associated with amyloid-like glomerular deposits. Nephron 18: 301-308, 1977 4. Duffy JL, Khurana E, Susin M, et al: Fibrillary renal deposits and nephritis. Am J Pathol 113:279-290, 1983 5. Korbet SM, Schwartz MM, Rosenberg BF, et al: Immunotactoid giomerulopathy. Medicine (Baltimore) 64:228243, 1985 6. Korbet SM, Rosenberg BF, Schwartz MM, et al: Course of renal transplantation in immunotactoid glomerulopathy. Am J Med 89:91-95, 1990 7. Korbet SM, Schwartz MM, Lewis EJ: Immunotactoid glomerulopathy. Am J Kidney Dis 17:247-257, 1991
Reply: In their letter, Drs. Lewis, Korbet, and Schwartz present a viewpoint expounded in their previous considerations of this topiC,I.2 that immunotactoid g1omerulopathy (IT) is a unifying diagnosis for patients whose renal biopsies show deposition of nonamyloidotic fibrillar or microtubular deposits. In their view, this term encompasses cases that exhibit only " subtle differences in morphology and size." The article 3 that elicited their letter suggested othelWise, and identified morphological features characteristic of what has been called fibrillary nephritis or fibrillary g1omerulonephritis··5 that are distinct from the lesion of IT as first illustrated by Lewis and Schwartz6
before the term, as used by them. evolved to include a broader spectrum of patients. Whether the differences identified are su btle or not will not be settled by argument. Instead, I invite readers to examine Figs II through 13 from different cases in the series of patients reported by Korbet et al. 1 and decide if the lesions illustrated are subtle variations on a theme or easily distinguishable patterns of deposits. In my view, the dissimilarities of these lesions are striking. Further, as demonstrated in Table I of my article, it is apparent that fibril/microtubule size is an objective discriminant that provides a nearly complete separation of the two entities. Finally, the cases themselves exhibit no overlap-
198
REFERENCES
American Journal of Kidney Diseases, Vol XX, No 2 (August), 1992: pp 198-201
IMMUNOTACTOID GLOMERULOPATHY
is learned of its origin. Until then , in our opinion, the "splitters" among taxonomists do not offer any advantage over the "Iumpers," as there is no practical value to a proliferation of diagnostic terms based on ultrastructural variances of no known significance. In the meantime, while we learn more of this unusual glomerular deposit, the cause of glomerular taxonomy is not served by those who misuse an othelWise useful term in an effort to apply their own. The literature about this lesion is now growing in an informative manner. This alone provides a barometer for the value of the recognition and labeling of the lesion known as immunotactoid g1omerulopathy. Edmund J. Lewis, MD Stephen M. Korbel, MD Melvin M . Schwartz, MD Rush Medical College Chicago,IL
To the Editor: It is true that in nephrology, as in all scientific endeavors, it is the burden of the taxonomist to develop useful systems of classification. These systems serve to clarify the similarity or identity of certain characteristics among individuals or groups of individuals. Hence the categorization of renal pathology according to established morphological criteria plays an important role in our perceptions about disease processes and ways in which they may be studied and treated. The purpose of taxonomy is therefore one of clarification. It is unfortunate that we occasionally fail and an erroneous classification may only serve to confuse the situation. The article by Alpers l entitled "Immunotactoid (Microtubular) glomerulopathy: An entity distinct from fibrillary glomerulonephritis?" is a regrettable example of the latter. The term "immunotactoid g1omerulopathy (ITG)" was coined in order to introduce the lesion to the nephrology community in unambiguous terms.2 Other descriptions such as " congo-red negative amyloid"3 and " fibrillary glomerulonephritis,'" which emphasize the ultrastructural appearance of the deposits while ignoring their immunoglobulin content, seemed less able to communicate the unique nature of this clinicopathological entity. Hence, nephrologists and pathologists were alerted to (I) the existence of this unusual glomerulopathy; (2) the need for a thorough evaluation to rule out other systemic diseases associated with organized deposits composed of immunoglobulin, such as cryoglobulinemia (which is illustrated in the case presented by Dr Alpers), paraproteinemias (demonstrated in much of the literature selected by Dr Alpers to support his argument), and systemic lupus erythematosus; (3) distinguish this lesion from amyloid, a lesion for which it had previously been mistaken, and (4) the clinical course experienced by patients with this clinicopathological entity before and after renal transplantation. 5• 7 Because subtle differences in the morphology and size of the organized material in ITG are of unknown clinical significance, we must reserve judgement until something more
I. Alpers CE: Immunotactoid (microtubular) g1omerulopathy: An entity distinct from fibrillary glomerulonephritis? Am J Kidney Dis 19:185-191 , 1992 2. Schwartz MM, Lewis EJ: The quarterly case: Nephrotic syndrome in a middle-aged man. Ultrastruct Pathol 1:575582, 1980 3. Rosenmann E, Eliakim M: Nephrotic syndrome associated with amyloid-like glomerular deposits. Nephron 18: 301-308, 1977 4. Duffy JL, Khurana E, Susin M, et al: Fibrillary renal deposits and nephritis. Am J Pathol 113:279-290, 1983 5. Korbet SM, Schwartz MM, Rosenberg BF, et al: Immunotactoid giomerulopathy. Medicine (Baltimore) 64:228243, 1985 6. Korbet SM, Rosenberg BF, Schwartz MM, et al: Course of renal transplantation in immunotactoid glomerulopathy. Am J Med 89:91-95, 1990 7. Korbet SM, Schwartz MM, Lewis EJ: Immunotactoid glomerulopathy. Am J Kidney Dis 17:247-257, 1991
Reply: In their letter, Drs. Lewis, Korbet, and Schwartz present a viewpoint expounded in their previous considerations of this topiC,I.2 that immunotactoid g1omerulopathy (IT) is a unifying diagnosis for patients whose renal biopsies show deposition of nonamyloidotic fibrillar or microtubular deposits. In their view, this term encompasses cases that exhibit only " subtle differences in morphology and size." The article 3 that elicited their letter suggested othelWise, and identified morphological features characteristic of what has been called fibrillary nephritis or fibrillary g1omerulonephritis··5 that are distinct from the lesion of IT as first illustrated by Lewis and Schwartz6
before the term, as used by them. evolved to include a broader spectrum of patients. Whether the differences identified are su btle or not will not be settled by argument. Instead, I invite readers to examine Figs II through 13 from different cases in the series of patients reported by Korbet et al. 1 and decide if the lesions illustrated are subtle variations on a theme or easily distinguishable patterns of deposits. In my view, the dissimilarities of these lesions are striking. Further, as demonstrated in Table I of my article, it is apparent that fibril/microtubule size is an objective discriminant that provides a nearly complete separation of the two entities. Finally, the cases themselves exhibit no overlap-
198
REFERENCES
American Journal of Kidney Diseases, Vol XX, No 2 (August), 1992: pp 198-201
