Progressive multifocal
leukoencephalopathy (PML)

June 2007     View PDF     En español

How do you diagnose PML?

Diagnosing PML is tricky. PML, toxoplasmosis, AIDS dementia complex, cryptococcal meningitis and lymphoma, CMV and even herpes virus infections in the brain can appear like one another on an MRI scan, a type of x-ray of the brain. All of these conditions have been associated with HIV. Because the lesions can look similar on an MRI, it’s important to continue the diagnosis by doing a brain biopsy. This way the exact cause can be determined and treated properly. A small hole is drilled into the skull and a piece of tissue is removed and examined. If the JC virus is found in the tissue, PML is diagnosed. A brain biopsy is considered the gold standard for diagnosing PML.

Some people who are presumed to have PML will elect not to have a brain biopsy. Doctors, as well as some surgeons, may not recommend it because it is invasive and causes discomfort. Even if a definite diagnosis of PML comes back, no therapies are very effective at treating the condition with the exception of changes in anti-HIV therapy. A doctor and patient may opt to make these changes regardless of a definitive PML diagnosis.

The main benefit of doing a biopsy is to rule out other possible brain diseases that may be more readily treated. If a person decides not to have the biopsy to confirm PML, doctors sometimes still recommend treating these other common brain diseases on the off chance that the condition is treatable.

When the brain biopsy is not done, PML will be diagnosed using three pieces of information. This includes: 1) if the state of health is consistent with PML symptoms; 2) if JC virus DNA is present in the cerebral spinal fluid; and 3) if MRI tests show lesions mainly in the brain’s white matter. However, using anti-HIV therapy complicates the choice to do a brain biopsy in diagnosing PML. The lesions may look different, including more inflammation than what’s normally seen, when potent anti-HIV therapy is used.

Another form of x-ray called a computed tomographic (CT) scan may show problems in the brain, but it is not as sensitive as an MRI. Testing for antibodies to the JC virus in blood or urine is also not a good way to detect active JC virus. This is because up to 4 in 5 adults already have these antibodies, with or without HIV infection.
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