BK virus: A clinical review

We present a review of the clinically oriented literature about BK virus, a relative of JC virus, which is the etiologic agent of progressive multifoc al leukoencephalopathy (PML). The kidney, lung, eye, liver, and brain have been proposed as sites of BK virus-associated disease, both primary and rea ctivated. BK virus has also been detected in tissue specimens from a variet y of neoplasms. We believe that BK virus is most often permissively present in sites of disease in immunosuppressed patients, rather than being an eti ologic agent that causes symptoms or pathologic findings. There is, however , strong evidence for BK virus-associated hemorrhagic cystitis and nephriti s, especially in recipients of solid organ or bone marrow transplants. Now that BK virus can be identified by use of specific and sensitive techniques , careful evaluation of the clinical and pathologic presentations of patien ts with BK virus will allow us to form a clearer picture of viral-associate d pathophysiology in many organ systems.