By Merritt McKinney, Medical Tribune News Service
A widely available brain scan used in conjunction with an
experimental drug may identify Parkinson's disease early, before
there are any symptoms, a preliminary study suggests. Detecting the
disease in its early stages with this ``brain mammogram'' may help
stop the illness in its tracks, if drugs under development prove
effective in preventing symptoms like tremors and rigid movement,
the study's authors report.
``For every case of Parkinson's disease in the elderly, it's
estimated that there are 10 presymptomatic cases walking around,''
according to the lead investigator, Dr. Demetrius M. Maraganore, an
associate professor of neurology at the Mayo Clinic in Rochester,
Minn. ``Our concern is that as the population continues to live
longer, more and more of these cases will become symptomatic.''
``We have a challenge before us'' to detect Parkinson's, which
is a progressive and degenerative neurological disease, before it
causes symptoms, he said.
People with Parkinson's disease have a severe shortage of a
brain chemical called dopamine. The chemical, which is a
neurotransmitter, is essential for certain brain cells involved in
controlling movement. A decline in dopamine levels causes these
brain cells to degenerate.
When a person takes a dose of beta CIT, the radioactive
medication used in the study, it binds to these dopamine-dependent
brain cells, according to Maraganore. Using a scan called
single-photon emission computed tomography (SPECT), the researchers
were able to detect beta CIT in the brain. Low levels of beta CIT
signify deterioration in the section of the brain known as the
striatum.
Not surprisingly, levels of visible beta CIT were lower in 10
people with Parkinson's disease than in 10 people without the
disease or in a control group of 10 people who had a family history
of Parkinson's, the researchers reported in the July issue of Mayo
Clinic Proceedings. But beta CIT levels in the family history group
were lower than in the control group, leading Maraganore and his
colleagues to suspect early stages of Parkinson's. And levels were
lower in family members who had the greatest risk of developing the
disease, either because they had more than one relative with
Parkinson's or because they had at least one symptom.
In order for a person to be diagnosed with Parkinson's disease,
at least two major symptoms must be present, according to
Maraganore. The Minnesota neurologist estimated that about 3
percent of the population will develop Parkinson's disease.
However, the risk triples when one close relative has the illness
and jumps to 30 percent if two relatives are affected, he said.
Maraganore called the detection procedure a ``kind of
mammography of the brain.'' Just as early detection of breast
cancers often results in more promising treatment, he said he hopes
that the same may be true with Parkinson's one day soon.
Although another test known as PET can detect early signs of
Parkinson's disease, it is only available in a handful of research
centers around the country, he noted. On the other hand, most large
medical centers already have SPECT cameras, he said.
Beta CIT has not been approved by the federal Food and Drug
Administration. Its maker, Guilford Pharmaceuticals, provided
funding for the current study, as did the Mayo Foundation and the
National Institute of Neurological Disorders and Stroke.
Using SPECT and beta CIT to detect Parkinson's ``might be very
important'' in the future, commented Dr. William G. Ondo, an
assistant professor of neurology at Baylor College of Medicine in
Houston.
But for the test to be useful, drugs under development that aim
to prevent the damage caused by the disease will have to be proven
effective, he cautioned.
Assuming such treatments do work, then early detection will be
essential for preventing symptoms, according to Maraganore.
Unfortunately, most of such drugs are in ``the pipe-dream
stage,'' said Dr. Caroline M. Tanner, the director of clinical
research and patient services at the Parkinson's Institute in
Sunnyvale, Calif. So far, no one has been able to stop or slow down
Parkinson's disease, she noted. And while Tanner said the study is
``a step in the right direction,'' she cautioned against reading
too much into the findings.
``We need to be really careful,'' she noted, since whether the
high-risk people in the study definitely will develop Parkinson's
disease remains to be seen.
