liv poz mag.qxd - Positive Living BC

Opportunistic Infections
PML is a rare disease of the central
nervous system that affects
immunocompromised people
by Leslie Leung
was 1971, and John Cunningham felt progressively weak on
Itone side of his body. His eyes had become blurry over the
previous month. He frequently lost balance. He couldn’t think
straight. After a series of investigations, doctors determined he
had a condition called progressive multifocal leukoencephalopathy
(PML). The term sounds fancy, but doctors at that time
actually knew very little about the disease. All they knew was
that people with PML had a weak immune system and that a
virus could be potentially causing the disease. It was from John
Cunningham’s brain that Billie L. Padgett, a researcher from
University of Wisconsin, first isolated the PML-causing virus,
which he thus named the JC virus.
Today, most cases of PML are among people with HIV;
fortunately, it’s very rare.
Ninety percent of the population harbours the JC virus. It
enters our system through inhaling or ingesting contaminated
water during childhood or early adulthood. It then sleeps in
our kidneys, tonsils, and bone marrow. Most of us don’t get
PML because our immune system keeps the JC virus in check.
However, the virus can infect the brain, causing PML in cases
where our immune system is disrupted—for example, certain
types of lymphoma, use of immunosuppressant drugs, and
HIV infection.
In fact, 85 percent of all PML cases are from HIV infection.
However, less than one percent of HIV-infected people actually
acquire the disease. In most cases, PML occurs in a person with
AIDS where immunosuppression is severe from low CD4
counts under 100. Unlike other opportunistic infections, PML
can occur in people with CD4 counts greater than 200.
Since the JC virus infects areas of the brain disrupting the
transfer of nervous signals, PML can lead to sensory and motor
problems. The most common symptom is limb weakness,
which occurs in 52 percent of cases. Thirty to 40 percent of all
cases involve decline in cognitive function, visual field loss, and
difficulty speaking. Headaches, seizures, loss of movement control,
and memory loss can occur, though they’re more rare.
Without proper diagnosis or intervention, people with PML
rapidly deteriorate and die within six months.
Because PML shares symptoms similar to other AIDSdefining
infections of the central nervous system, doctors
need to perform special procedures to diagnose the disease.
There are generally three things doctors might do if you
have any of the symptoms of PML. First, doctors might
take snapshots of your brain using a CT scan or an MRI to
check for any abnormal lesions. Second, doctors might
collect cerebrospinal fluid from your spine to see whether
the JC virus is active in your central nervous system.
Finally, doctors might obtain a sample of your brain tissue
and look under the microscope for the JC virus.
Unfortunately, there’s no known cure or a specific
treatment for PML. Several drugs have been tested, but haven’t
been proven to work. To date, the only therapy that has been
shown to be indirectly beneficial for PML management is
highly active antiretroviral therapy (HAART). HAART should
be initiated or continued in people diagnosed with PML
regardless of their CD4 count; the rationale is that a boost in
the immune system can keep the JC virus in check. In fact,
studies have shown that HAART increases the mean survival
time of PML. 5
Leslie Leung is a University of British Columbia
medical student and a community pharmacist.
He volunteers with BCPWA’s
Treatment Information Program.
MayqJune 2010 living5 31