What is your diagnosis in this renal allograft biopsy?
This photomicrograph shows a background of lymphocytic inflammation and a tubular profile with several enlarged tubular epithelial cells. Within these cells, the nuclei are enlarged and often hypochromatic. Additionally, within the cytoplasm, numerous hyperchromatic inclusion bodies are seen. These findings are consistent with viral cytopathic changes and are highly suspicious for virus-induced nephritis. In renal allografts, BK nephritis is the most commonly seen virus-induced nephritis. However, while the morphology of viral inclusions cannot definitively categorize the etiology, BK nephritis tends toward enlarged and hyperchromatic nuclei with smudgy intranuclear inclusions. Adenovirus can also be seen in renal allografts but is extremely rare and typically shows a wide range of viral morphologic changes. Often helpful in adenovirus is the frequent presence of intratubular granuloma-like accumulations of epithelial cells and histiocytes which can be quite exuberant in some cases. Finally, CMV can also occur in renal allografts and has a wide range of nuclear and cytoplasmic inclusion morphologies. However, it can often create hypochromatic nuclear changes, even sometimes with ‘cherry red’ nuclei (as seen below). In all cases of viral nephritis further immunohistochemical stains are indicated (not shown) and in this case, CMV was indeed positive consistent with CMV-mediated nephritis.
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