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Hi all, This is as I understand it, but of course this is also based upon the opinions of some (IMO rather knowledgable) neurologists, and others may (partly) disagree. Parkinson's Disease is mainly diagnosed upon the story of the symptoms that the patient tells to the doctor. Only after death an autopsy can for certain confirm the diagnosis PD. In about 15-20% of the cases investigated after death, the diagnosis is found to have been something else than PD. It is hard to diagnose PD, though symptoms appear to be clearly pointing in that direction. It is even more difficult in the beginning and/or with younger patients. So the doctor looks for other ways to support the diagnosis PD. These investigations do NOT diagnose PD either, but enlarge the probability of the (in)correctness of the diagnosis. Time is one of the factors. In time the symptoms get worse and support the diagnosis. Also a positive response to levodopa is support for a diagnosis of PD. MRI is mainly used to exclude other illnesses like braintumors and other anatomical disorders in the brain. What then remains are the SPECT and PET scans. The main difference between a SPECT and a PET scan is, that a PET scans the brain while the patient is active, like walking on a treadmill or a making large movements. SPECT scans the brain while the patient is in rest, like lying on his back. Because of the more complicated technique the PET is (much) more expensive and the SPECT is more commonly used and available. For (supporting) the PD diagnosis SPECT is (almost) as good as a PET. SPECT & PET scans can be used for two purposes, using different radioactive agents called "tracers" (fluor-dopa and 1,2,3-Iodine are examples of tracers): 1 is it PD or something like that or NOT (targetting the dopamine concentrations). 2 is it PD or MSA (targetting the numbers of dopamine-receptors). Note that also a PET or SPECT scan is not capable of definitely diagnosing PD or MSA, it is only an enhancing tool for making the diagnosis (when doubted after -several- visits to the neurologist considering symptoms and progress) more (or less) probable. Some neurologists attach great importance to a SPECT (or PET), while others do not find the results of a SPECT (or PET) that significant. Research in the reliability of SPECT & PET scans are not conclusive about that. In practice the results of a SPECT (or PET) scan are either confirming or denying the doctors opinion, and accordingly the further treatment is set out. Besides the point that (only) a SPECT (or PET) is not able to give a definite diagnosis, MONEY plays a major part in why they don't give every suspected PWP a SPECT (or PET) scan. Waiting for a year and meanwhile giving levodopa is much cheaper and (most of the time) as conclusive regarding the correct diagnosis as a SPECT (or PET). Note also that in a starting PWP the alterations in the substantia nigra are still very little and not easy to interprete. Problem cases (difficulty in diagnosis and/or treatment) after a few years often DO get a SPECT (or PET) scan (probably not only for the patients, but also for the doctors peace of mind). But problem cases often get second, third or fourth, etc opinions with different doctors and they may (all) come up with different diagnoses !! That can happen, because the main part of diagnosis is still the story of the patient about his symptoms and the interpretation of each doctor of those gathered data. Obvious is that the patient gets very confused. Hans. ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn