Progressive Multifocal Leukoencephalopathy
What is Progressive Multifocal Leukoencephalopathy?
Progressive multifocal leukoencephalopathy (PML) is
caused by the reactivation of a common virus in the central nervous system of
immune-compromised individuals. Polyomavirus JC (often called JC virus) is
carried by a majority of people and is harmless except among those with lowered
immune defenses. The disease occurs, rarely, in organ transplant patients;
people undergoing chronic corticosteroid or immunosuppressive therapy; and
individuals with cancer, such as Hodgkin’s disease, lymphoma, and sarcoidosis.
PML is most common among individuals with acquired immune deficiency syndrome
(AIDS). Studies estimate that prior to effective antiretroviral therapy, as many
as 5 percent of people with AIDS eventually developed PML. For them, the disease
was most often rapidly fatal.
With current HIV therapy, which effectively restores
immune system function, as many as half of all HIV-PML patients survive,
although they sometimes have an inflammatory reaction in the regions affected by
PML. The symptoms of PML are the result of an infection that causes the loss of
white matter (which is made up of myelin, a substance the surrounds and protects
nerve fibers) in multiple areas of the brain. Without the protection of myelin,
nerve signals can’t travel successfully from the brain to the rest of the body.
Typical symptoms associated with PML are diverse, since they are related to the
location and amount of damage in the brain, and evolve over the course of
several days to several weeks. The most prominent symptoms are clumsiness;
progressive weakness; and visual, speech, and sometimes, personality changes.
The progression of deficits leads to life-threatening disability and death over
weeks to months. A positive diagnosis of PML can be made on brain biopsy, or by
combining observation of a progressive course of the disease, consistent white
matter lesions visible on a magnetic resonance image (MRI) scan, and the
detection of the JC virus in spinal fluid.
Is there any treatment?
Currently, the best available therapy is reversal of
the immune-deficient state. This can sometimes be accomplished by alteration of
chemotherapy or immunosuppression (even if it means losing non-vital
transplanted organs). In the case of HIV-associated PML, immediately beginning
anti-retroviral therapy will benefit most individuals.
What is the prognosis?
The mortality rates for those with HIV-PML have fallen
dramatically from approximately 90 percent to around 50 percent according to
most reports. For non-AIDS individuals with PML, the prognosis remains grim; the
disease usually lasts for months and 80 percent die within the first 6 months,
although spontaneous improvement has been reported. Those who survive PML can be
left with severe neurological disabilities.
What research is being done?
The National Institute of Neurological Disorders and
Stroke (NINDS) and other institutes of the National Institutes of Health (NIH)
conduct research related to PML in laboratories at the NIH, and support
additional research through grants to major medical institutions across the
country. Much of this research focuses on finding better ways to prevent, treat,
and ultimately cure disorders such as PML.
National Organization for Rare Disorders (NORD)
P.O. Box 1968
(55 Kenosia Avenue)
Danbury, CT 06813-1968
Tel: 203.744.0100 Voice Mail 800.999.NORD (6673)
Source: National Institutes of Health; National Institute of Neurological Disorders and Stroke