Striped pattern of medullary ray fibrosis in allograft biopsies from kidney transplant recipients maintained on tacrolimus

Background. A striped pattern of fibrosis has been described in the kidneys of patients undergoing longterm cyclosporine or tacrolimus therapy. This lesion is frequently misconstrued as being specific for drug toxicity. Methods. We performed clinicopathologic correlation on 18 patients with striped fibrosis identified by reviewing 61 biopsies from kidney transplant recipients maintained with tacrolimus. Results. Acute rejection was identified in 14 of 18 patients, chronic rejection in 9 of 18 patients, potential diabetic microvascular injury in 8 of 18, and pre-existing donor disease in 2 of 18. In only one patient could striped fibrosis be ascribed primarily to tacrolimus. Striped fibrosis could also be demonstrated in 6 of 10 late allograft biopsy specimens from patients maintained with only azathioprine, and 8 of 10 native biopsies from patients with advanced diabetes mellitus. Conclusion. Multiple insults contribute to the pathogenesis of striped fibrosis in the kidney. This lesion can be attributed entirely to chronic drug toxicity in only a minority of allografts.