Acute antibody-mediated rejection limited to medullary lesions in following ABO-incompatible living donor kidney transplantation.

Anatomical differences between the renal cortex and medulla may influence inflammatory responses. Owing to the difficulty in diagnosing rejections from the medulla, rejection is usually diagnosed through the cortex. However, previous studies have shown that there are no significant differences in renal cortical and medullary lesions in acute allograft rejection. A 60-year-old man with a history of diabetic nephropathy underwent kidney transplant from a living unrelated donor at our hospital in August 2019. Three days after surgery, his urine output suddenly decreased, whereas the serum creatinine levels increased. A kidney biopsy showed only medullary lesions with positive C4d-staining and a Banff score of PTC grade 3. He was diagnosed with acute antibody-mediated rejection (AMR) and treatment was initiated. He did not respond to conventional treatments, including plasma exchange and intravenous immunoglobulin, but his general condition improved after bortezomib administration. There have been a few cases of acute AMR limited to medullary lesions. We consider that rejection cannot be excluded even if the lesions are confined to the medulla.