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Diagnosis: Chronic active T-cell-mediated rejection with superimposed acute rejection and presence of crescents

It is difficult to know with certainty whether we are dealing with a proliferative GN (with crescents) superimposed upon an chronic rejection or with severe glomerular changes due to rejection. Crescents can be seen in virtually any severe renal disease. Thus the question as to whether this is a severe form of immune response against the allograft, or an underlying superimposed glomerulonephritis. The total lack of immune complexes would certainly be against a GN, and there was no clinical evidence for any underlying condition which would like to immune complex deposition. ANCAs were negative. Thus we are left with the notion that crescents are consecuence of severe acute cellular rejection superimposed to chronic rejection.

Although everyone understands what a well-formed crescent is and how to diagnosis it, it is likely that occasionally renal pathologist will disagree whether a crescent is present in a specific biopsy or glomerulus. The definition of a "crescent" is "extracapillary (glomerular) hypercellularity other than the epithelial hyperplasia of collapsing variant of focal segmental glomerulosclerosis" (Jennette C. et al. Heptinstall's Pathology of the Kidney, 6th edition, 2007). We interpreted that these glomerular changes represent crescent formation.

The "concordance" (agreement) between experienced renal pathologists as to what is indeed "crescentic GN" and what is not, is over 95% (Silva F, Dalton RR. Renal Pathology case. 2006 USCAP 2006 annual meeting. http://www.uscap.org/).

In the past the percentage of glomeruli harboring crescents to be able to give the diagnosis of diffuse extracapillary (crescentic) glomerulonephritis was a bit arbitrary, with some authors calling it a crescentic GN with as few as 20-30% of glomeruli, whereas others did not think the percentage of glomeruli harboring crescents was clinically meaningful (in terms of prognosis) until 80% of them had crescents. Although still somewhat arbitrary, most authors now require approximately 50% of the glomeruli to harbor crescents in order to diagnose "crescentic GN". Certainly, if one has less than 50% crescents, there is still room for bad prognosis, and the diagnostic report should indicate what percentage of glomeruli have crescents (Silva F, Dalton RR. Renal Pathology case. 2006 USCAP 2006 annual meeting. http://www.uscap.org/).

Thus, in this patient, the changes were not called "crescentic GN", but the phrase "with crescent formation" was added to the end of the diagnosis (with the percentage of glomeruli involved stated).

For the best of our knowledge, there are not studies determining frequency and/or characteristics of crescents in rejection. Then, it is not possible to know pathogenic mechanisms neither clinical implications. Antibody mediated rejection (AMR) frequently produces glomerulitis, sometimes severe; it is possible that this humoral response against glomeruli in the allograft produces epithelial damage and crescents formation, however, in the present case we do not found histologic or immunopathologic signs suggesting AMR, then, we think that T-cell-mediated mechanisms could be implicated in its develop.

See the chapter Crescentic Glomerulonephritis in our Tutorial.

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Bibliography

• Jennette C. et al. Heptinstall's Pathology of the Kidney, 6th edition, 2007.
• Silva F, Dalton RR. Renal Pathology case. 2006 USCAP 2006 annual meeting. http://www.uscap.org/

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