How is progressive multifocal leukoencephalopathy (PML) diagnosed? Should I worry?

PML is a brain infection that is caused by the JC virus. Exposure to this virus is common, but it generally causes problems only in patients who have been treated with aggressive immunosuppressive therapy, such as chemotherapy for cancer. PML has also been reported in patients receiving drugs to treat rheumatic or autoimmune diseases, such as lupus and rheumatoid arthritis, although this is extraordinarily rare. PML is diagnosed by brain autopsy or by looking for evidence of the JC virus in cerebrospinal fluid (CSF) obtained by lumbar puncture (spinal tap), using a technique called polymerase chain reaction. Because neither brain biopsy or CSF examination is perfect, it is generally recommended that such tests are performed only when the suspicion of PML is very high.

(Click the back button in your browser to go back to the FAQ page.)