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.
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