Atlas of Nontumor Pathology: Non-Neoplastic Kidney Diseases

D'Agati VD et al. (2005) Atlas of Nontumor Pathology: Non-Neoplastic Kidney Diseases. Maryland: ARP Press

This book is a visual feast for renal histopathologists. Its creation has been made possible by improvements in digital image acquisition and reductions in the cost of color reproduction. For the first time ever, I am left wondering whether this book actually has too many photomicrographs. The illustrations accompanying the section on acute tubular necrosis alone run to 25 high-quality images, and that is just the slides stained with hematoxylin and eosin. Is this excessive? It is an unfamiliar question. The accompanying descriptions do not disappoint. They comply firmly with the tradition of the Armed Forces Institute of Pathology atlases; they are comprehensive, detailed and authoritative. So could a renal histopathologist have any complaint about this book?

Well actually, yes. For a diagnostician attempting to classify the morphological appearance of a renal biopsy specimen, the book is splendid. There is, however (probably by deliberate choice: it describes itself as an atlas), relatively little information on pathogenesis or clinical significance. Consequently, this is an ideal book for a renal histopathologist who works in isolation from nephrologists—but that is not how renal histopathologists ought to work.

The limited consideration of pathogenesis perhaps explains some other peculiarities of the book. Classifying renal disease is difficult. The structured categorization familiar to tumor pathologists is not possible in renal pathology because many inflammatory or immunological renal diseases could fit into several possible disease groupings. I suspect that if 10 renal histopathologists were asked to draw up a classification of renal disease, the result would be at least 15 different classifications; so perhaps complaints about the organization of the book are unfair. But it does have some rather inexplicable features; for example, the classification of focal segmental glomerulosclerosis (FSGS). The term FSGS is notorious for causing confusion, because it can be used simply as a description of segmental glomerular scarring from any cause, or to denote a nephrotic renal disease that has a tendency to progress inexorably to renal failure and to recur in transplanted kidneys. The situation has recently been clarified by the development of a new classification of FSGS, in which two of the authors of this book were heavily involved.¹ Why then does the classification of FSGS offered here add C1q nephropathy to the list of FSGS variants? As the authors clearly explain, C1q nephropathy is unequivocally an immune-complex-mediated disorder. It can cause segmental scarring but, in pathogenetic terms, it is completely distinct from 'primary' FSGS. One could just as logically describe IgA nephropathy or systemic lupus erythematosus as forms of FSGS.

The authors encourage fine subdivisions of classification, but they neglect to explain the clinical relevance of these divisions. For example, a variation on Ehrenreich and Churg's “stages” of membranous nephropathy² is offered. The potential reproducibility of a classification based on vague descriptions of the glomerular basement membrane such as “slightly thickened”, “moderately thickened”, and “markedly thickened” is not discussed, nor is the fact that in almost 40 years since its description, this classification has not been proven useful in clinical practice. Similarly, the classification of membranoproliferative glomerulonephritis (MPGN) describes types I, II and III, ignoring the fact that many investigators question whether identifying type III is useful. Indeed, the authors go further and place considerable stress on subclassifying type III into two different patterns. There is no attempt to justify this. Furthermore, one could read the text without realizing that separate identification of MPGN type II really does matter, because this type has been shown to have a different cause (dysregulation of complement activation), a different pattern of presentation (younger age, no association with viral infection) and a higher rate of recurrence in transplanted kidneys than types I and III. Subclassification of diseases without reference to clinical relevance is fine as a research activity, but rather questionable in clinical practice.

Perhaps the most striking difficulty of classification arises in the chapter entitled “Hereditary Nephropathies”. The apparently comprehensive title of the chapter is misleading; preceding chapters include “Congenital Abnormalities including Cystic Diseases” and “Congenital Nephrotic Syndrome”. Fibronectin nephropathy is described elsewhere, under “Glomerular Diseases with Paraproteinemia or Organized Deposits”. So “Hereditary Nephropathies” deals with Alport syndrome (which is referred to as “hereditary nephritis” in the text and figure legends), thin basement membrane disease and a few other rare conditions that do not fit elsewhere. There are good illustrations of the diagnostic appearance of nail-patella syndrome, but the description of this condition is found only in the context of the differential diagnosis of Alport syndrome. This chapter should be entitled “Other Hereditary Nephropathies” and come at the end of the book, but it is actually near the beginning.

Rereading these criticisms, I suspect I am being harsh. The book is intended purely for diagnostic histopathologists who have a responsibility for reporting renal biopsy findings. In that respect, it fulfils its aim admirably. I just have a slightly uneasy feeling that morphologic classification has taken an unjustified precedence over actually trying to understand what is happening in the kidney.

Of recent publications, the most significant competition for this book is probably Fogo and Kashgarian's Diagnostic Atlas of Renal Pathology.³ When I opened that book, I thought the illustrations were the best I had ever seen; but D'Agati et al. have beaten it. Their descriptions are more comprehensive than Fogo and Kashgarian's—the book is almost twice the length—but the approach to classification, pathogenesis and clinical relevance is, in my view, better in Fogo and Kashgarian, despite that book setting out to be a pathologist's addition to Brenner and Rector's huge nephrological tome. Affluent pathology departments will undoubtedly want to possess a copy of both Non-Neoplastic Kidney Diseases and the Diagnostic Atlas of Renal Pathology. Less affluent ones will have to decide on the basis of personal preference; they cost almost the same amount. It is not an easy decision.