History:
History: 34 year old male with clinical suspicion of early-onset
Alzheimer disease.
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Figure
1 - Alzheimer |
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Figure
2 - normal |
Findings:
Axial PET image of the brain (figure1) demonstrates normal activity in
the frontal lobes (bright blue), with diminished activity in the
parietal, temporal, and occipital lobes. This pattern is typical of
Alzheimer disease. As a comparison, figure 2 is of a different patient
with normal brain activity.
Discussion:
Conventional imaging with CT and MR is
neither sensitive nor specific for the diagnosis of Alzheimer disease
(AD). Role of CT and MR in the work-up of dementia is primarily to
assess the degree of atrophy and to exclude other causes of dementia
such as normal-pressure hydrocephalus, multi-infarct dementia, and
intracranial mass.
PET has been used in scanning the brain
by evaluating the metabolic uptake of glucose-analogue FDG. High
accuracy in differentiating AD from other forms of dementia has been
reported. In patients with AD, deficits in temporoparietal metabolism
are typically seen. Sensitivity of 94% has been reported in the
literature (J Nucl Med 1994; 35:391-398), with high accuracy seen in
early and mild forms of the disease. Abnormal temporoparietal uptake
has also been demonstrated in asymptomatic patients with family
history of early-onset AD (Ann Neurol 1997; 42:85-94). In a
multinational consortium study (JAMA 2001; 286:2120-2127), PET
accurately predicted cognitive decline in patients with AD, with
sensitivity of 93%.
In 2004, Medicare approved coverage for
PET scans in the early diagnosis of Alzheimer's Disease. This is
an important step in the management of AD patients, as new drugs work
best in the early stages to slow the progression of this disease.
PET offers information not available
through other types of diagnostic studies. Since PET tracer FDG is
taken up at a cellular level, functional images are generated that
complement the traditional anatomic images generated through CT and
MRI studies.
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