Discussion

DR. ROBERT B. COLVIN (Chief Department of Pathology, Mas-sachusetts General Hospital, and Benjamin Castleman Professor of Pathology, Harvard Medical School, Boston, Massachusetts, USA): Let me begin with a brief comment on this case. The first allograft biopsy showed donor vascular disease but no evidence of rejection. The lack of tubular and vascular changes was consistent with mild CsA toxicity. Accordingly, the CsA dose was reduced with beneficial results. The second biopsy also showed no evidence of active rejection. The vascular lesions had progressed and can be attributed to a combination of donor nephrosclerosis plus recurrent diabetic arteriopathy. The hyaline deposits were not diagnos-tic of chronic CsA toxicity, in which the hyaline replaces individual smooth muscles. The glomerular lesions are distinctive and typical of the collapsing variant of focal sclerosis, a process not known to be part of chronic rejection. I will return to the significance of this process later. In this Forum, I will update the current status of the renal biopsy in assessing renal allograft dysfunction, based on my prior review [1]. I will review classification, pathogenesis, diagnos-tic criteria, and differential diagnosis of allograft rejection and CsA toxicity.

As I stated previously, the renal biopsy remains the most definitive and reliable diagnostic test for graft rejection [11. The biopsy is more sensitive and more specific than radionuclide scintigraphy, fine-needle aspiration, or ultrasound [2]. Studies show that results of allograft biopsy can change the clinical diagnosis and/or treatment in approximately 40% of patients and spare these patients the risk and expense of unnecessary immu-nosuppression [3—51. Fortunately, percutaneous allograft biopsy is