PET Scans for the Diagnosis of Alzheimer’s Disease
AAGP Statement: April 2004
The National Institute on Aging (NIA) and the Centers for Medicare
and Medicaid Services (CMS) held
a meeting April 5 to discuss the role of positron emission tomography
(PET) using deoxy glucose in
the diagnosis of Alzheimer’s disease. Specifically, the meeting
was held to gather information—both scientific data and public
policy opinion—in order for CMS to revisit the issue of Medicare
reimbursement for PET scans.
The American Association for Geriatric Psychiatry (AAGP) and
the Alzheimer’s Association were the only two outside organizations
invited to present their positions. AAGP was represented by the
AAGP president, Anand Kumar, M.D., (2004-2005) and Christopher Colenda,
M.D., M.P.H., chair of AAGP’s Public Policy and Communications
Committee.
The opinion among those at the meeting was that PET scans need
to be limited to a few complex
cases and should not be used as a routine test for Alzheimer’s
disease (AD). The group was asked to consider the cost-effectiveness
of the scan and make decisions
on a case-by-case basis. As
a follow-up to the meeting, the CMS
asked meeting participants for responses to the following questions.
AAGP’s responses
follow.
Q: What minimal services must be performed and documented as pre-requisites
for ordering a PET scan?
A: A complete dementia work-up
that includes a comprehensive medical
exam, including a neurological
exam, a psychiatric exam, relevant
laboratory testing, and a neuropsychological battery (may be a condensed
battery)
should be performed. A structural
scan (CT/MRI) has also come to
represent the standard of care
in a dementia work-up. In special
circumstances, a PET FDG may provide
more information than an MRI/CT
scan, but that needs to be considered on an individual basis.
Q: Is a medical history alone sufficient
to ascertain six months of cognitive
decline or is actual observation
by a clinician necessary to assess
and document a decline over such
a period prior to ordering a PET scan?
A: When an informed/reliable caregiver
is available, collateral information
is often adequate to document six
months of decline. When reliable
collateral sources are not available,
actual observation may be needed.
Q: What qualifications must a practitioner
have to be considered “experienced in the diagnosis and assessment
of dementia”?
A: This is a very important issue:
Physicians trained in geriatrics
are critical in this regard. This
includes geriatric internists,
geriatric psychiatrists, and neurologists
with training in the area of cognitive
disorders. Family practitioners
with interest/expertise in geriatrics
will also qualify. Please
note that general internists, neurologists,
and psychiatrists may not have
sufficient expertise for a high
quality work-up. Adequate training
in geriatrics is critical.
Q: What type of facility or setting
is likely to offer the knowledgeable
and experienced interdisciplinary
staff needed to conduct a comprehensive
assessment and render an accurate
clinical diagnosis of dementia?
Can a minimum set of facility criteria
be identified that provide assurance
that a comprehensive assessment
will be performed? What set of skills and professions must
be assembled on the interdisciplinary
team?
A: The precise setting is less
critical than the qualifications/background
of the physician. A broad spectrum
of facilities ranging from academic
medical centers to private physician
offices will qualify, provided
the physician has the expertise
and background needed for a dementia
assessment. It is important to
get a comprehensive geriatric assessment
with interdisciplinary input before making
a final clinical diagnosis.
Q: A comprehensive work-up utilizing
the NINCDS-ADRDA criteria for clinical
diagnosis of Alzheimer’s
disease qualifies the likelihood of Alzheimer’s disease as “definite,” “probable,” “possible,” or “uncertain”.
Should PET be ordered only when
the comprehensive assessment results in an uncertain diagnosis?
A: Yes. PET scans should be reserved
for cases where the diagnosis
remains unclear after a complete
dementia work-up (see first response above)
and the physician is convinced
that a metabolic map of the brain
(i.e., an FDG PET scan) will
be of considerable benefit in making
a precise diagnosis. An additional
requirement might be that a PET-facilitated
diagnosis will alter the management
of a particular case. A PET scan
should not be part
of a routine dementia work-up.
It is far too expensive for that.
Q: What are the key differential
diagnoses among neurodegenerative
causes of dementia (e.g., frontotemporal
dementia vs. AD) that PET could
reasonably be expected to help
clarify after an experienced
clinician or team has completed
an assessment? What are those
clinical situations for which other
imaging or other tests would be better indicated
(e.g., distinguishing AD from
mixed AD-multi-infarct dementia)?
A: An MRI scan with a good
history and neurologic/medical
exam may be better than a PET
scan in assessing vascular burden
and thereby distinguishing AD
from MID. A comprehensive psychiatric
exam is necessary to distinguish clinically
between AD and depression in the
elderly (which can also have cognitive correlates).
Once again, the role of PET
in the differential diagnosis
cannot/should not be decided a
priori. It needs to be determined on a case-by-case
basis.
Q: What are the minimal educational
requirements for staff
performing and interpreting the
PET scans? How should test performance
and interpretation be standardized?
What accreditation requirements
must facilities performing
PET scans for AD meet?
A: This will vary. A nuclear
medicine physician/radiologist
with expertise in this
area or a physician with
geriatric experience (see third
response above) who has received
special training (workshop,
etc.) in reading PET
scans in the elderly may have
the required expertise.
No such formal training/certification
mechanism is in place and setting one up is likely
to be cumbersome.
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