The Pocket Smell Test (PST)-Alzheimer's Disease-Part XI
A full-page ad in the Journal of The American Geriatric Society suggests a new test to discriminate between Alzheimer’s disease and major depressive disorder. The ad actually reads that the test will "discriminate between probable Alzheimer’s disease and depression better than the Mini-Mental State Examination". Cursory reading might imply that this was a test for Alzheimer’s disease. The ad refers to a study in the Journal of Neuropsychiatry and Clinical Neuroscience (2000; 12:29-33), whose lead author was Robert McCaffrey.
Reviewing the McCaffrey study indicated that the "test" was a three-item microencapsulated "scratch and sniff" measure derived from a test called the "University of Pennsylvania Smell Identification test". On each item an odor is released and you choose one of four response alternatives. Two or more errors clearly distinguished individuals with probable Alzheimer’s disease as opposed to depressed subjects.
The theory behind this test is that the first area affected by neurotangle fibers, a distinguishing marker for Alzheimer’s disease, is the entorhinal cortex, one of the major components of the olfactory (smell) system. In depression, this area is not affected. The study also implies that age, gender and education do not systematically affect the Pocket Smell Test.
The authors of this study stress that PST "should not be used as the sole indication in the differential diagnosis of Alzheimer’s disease versus major depression". They go on to declare that "The PST is a brief, portable, inexpensive and user friendly measure that has been used successfully to discriminate between these two groups".
Since, up to now, no definitive diagnosis of Alzheimer’s disease can be made until a pathological examination of brain tissue after death is completed, and depression is a confounding variable in making a diagnosis of Alzheimer’s disease, the Pocket Smell Test may prove a valuable tool in the entire diagnostic process. It requires further clinical testing in groups that are not at the severe end of the scale of the two particular disorders and should be done in a double-blind manner with a control group and matched age groups. We will be on the lookout for further research studies in this area.
Harold Rubin, MS, ABD, CRC, Guest Lecturer
June 11, 2000
A recent review (April 2002) of the research literature has turned up new information about the olfactory test for Alzheimer’s disease. This information can be summarized, citing the conclusion of the Schiffman et al (8) research report: "Among chemosensory tasks, tests combining both olfactory and memory demands may be especially sensitive to changes occurring in Alzheimer’s disease. Areas of the entorhinal cortex and hippocampus are vulnerable to early neuroanantomical and metabolic changes occurring in Alzheimer’s disease. These areas are also involved with olfactory processing and with memory. Therefore, olfactory tests with a memory component can be uses as an additional tool for predicting Alzheimer’s disease." They were discussing familial risk evaluation for Alzheimer’s disease and were careful to use the words "additional tool" for prediction.
The present clinical diagnosis for possible Alzheimer’s disease makes use of a battery of neuropsychological tasks, clinical competence of the diagnostician, neuroimaging, and physical examination to rule out other possible diagnoses and can only be confirmed via autopsy. The need is to develop a screening device that may indicate early on the potential for Alzheimer’s disease. Interventions can then be started at an earlier stage of the disease and clinical support can be provided at this early stage.
There have been scattered reports of evidence suggesting that a diminished sense of smell is associated with Alzheimer’s disease. In 1987, Rezek (7) reported on olfactory deficits as a neurological sign in dementia of the Alzheimer type. Talamo (9) and his group examined changes in olfactory neurons in patients with Alzheimer’s disease. They indicated that there were histopathological changes in olfactory epithelium. In 1991, Hyman and colleagues (2) suggested that neuroanatomical and neurochemical changes related to Alzheimer’s disease occur in the olfactory bulb of the brain, confirming prior studies. Other areas that exhibited degeneration included the anterior olfactory nucleus, the olfactory tubercle, the uncus and the subiculum. These studies could be challenged on methodological grounds, but still carry some weight. It should be noted that Feldman and his associates (1) found that olfactory deficits are not the result of rhinologic pathology.
Mesholam et al (5), in 1998, did a meta-analysis of published papers on olfactory functioning in neurodegenerative disease including Alzheimer’s and Parkinson’s disease. The conclusion was that deficits occur in three olfactory domains: identification, recognition and threshold. This referred to the type of olfactory test performed. In an identification olfactory task, subjects are asked to identify odors form a list or those named by the experimenter. In a recognition/discrimination task, the goal is to recognize the presence of an odor or to determine if pairs of odors are identical, similar or different. In a threshold task, the lowest concentration at which odors could be detected was determined. (4, 6, 7).
Implied from these studies is the suggestion that olfactory sensation loss is associated with the early stages of Alzheimer’s disease and that the areas of the brain involved in this process may be involved with not only olfactory information but also memory consolidation. This does not seem true of the gustatory system as shown by Koss et al (3) in a study reported in the journal Neurology in 1988.
The take home message from all this research seems to be that olfactory tasks could become part of the armentarium used to clinically determine diagnosis of Alzheimer’s disease. It should not stand alone as a specific test for Alzheimer’s disease.
References:
For our other articles on Alzheimer's Disease-
See: Alzheimer's Disease Part I-Medications
for Alzheimer's.
See: Alzheimer’s Disease
Part II- Selegiline and AD.
See: Alzheimer's Disease Part III- Use of Gingko Biloba in memory problems of
Alzheimer patients.
See: Alzheimer's Disease PartIV-Alternative
Treatment.
See: Alzheimer's Disease Part V-Possible
New Drugs for Alzheimer's Disease Treatment.
See: Alzheimer's Part VI -Early
Diagnosis.
See: Alzheimer's Part VII -New
Medication-Metrifonate
See: Alzheimer's Part VIII-Implications
of Longer Life Expectancies
See: Alzheimer's Part IX-Ethical Care
Principles
See: Alzheimer's Disease Part X-Estrogen
and Alzheimer's Disease
See: Alzheimer's Disease Part XII-MAO-B
See: Alzheimer's Disease Part XIII-Critical
Flicker Fusion Threshold Test
See: Alzheimer's Disease Part XIV-Donepezil
See: Alzheimer's Disease Part XV-Cerebrolysin
See: Alzheimer's Disease Part XVI-MCI
See: Alzheimer's Disease Part XVII-Summary
See: Alzheimer's Disease Part XVIII-NO
Releasing NSAIDs
See: Alzheimer's Disease Part XIX-Vitamin
E
See: Alzheimer's Disease-Part XX-Clinical
Trials
See: Alzheimer's Disease Part XXI-The
Brain
See Dementia with Lewy Bodies- Part
XXII-by Gourete Broderick
See: Alzheimer's Disease-Part XXIII-HMG
See: Alzheimer's Disease-Part XXIV-A
Prequel
See: Alzheimer's Disease-Part XXV-Psychosis
See: Alzheimer's Disease-Part XXVI-Amyloid-beta
Hypothesis Controversy
See: Alzheimer's Disease-Part XXVII-
AD and Diabetes
See: Alzhemeir's Disease-Part XXVIII
- Insulin and AD
FOR AN INFORMATIVE AND PERSONAL ARTICLE ON PRACTICAL SUGGESTIONS WHEN SELECTING A NURSING HOME SEE OUR ARTICLE "HOW TO SELECT A NURSING HOME"
Harold Rubin, MS, ABD, CRC
Updated May 3, 2002
email: hrubin12@nyc.rr.com or rubin@brainlink.com