Polyomavirus nephritis

Polyomavirus nephritis (PVAN) is one of the most common viral complications in renal transplantation. It is in more than 97% of cases caused by BK virus in the context of BK virus nephritis and in less than 2% caused by JC virus. PVAN leads to graft loss in 30 to 80% of cases. Early diagnosis is therefore necessary to modify the immunosuppressive treatment and avoid graft loss. The diagnosis of PVAN is histological and combines tubulo-interstitial inflammation and a viral cytopathic effect in the form of nuclear inclusions of tubular cells. Tubular cell infection can be highlighted by immunohistochemical evidence of Sv-40 viral antigen expression. PVAN has histologic similarities to acute cellular rejection but the resulting treatments are diametrically opposed. One requires a decrease in immunosuppression while the other requires an increase in immunosuppression so accurate and early diagnosis is a major challenge.