Memory Disorders Clinic
The differential diagnosis of memory problems such mild cognitive impairment (MCI) and dementia is complex. Since there are many reversible causes of memory impairment (e.g., thyroid disease, infection, depression, nutritional deficiency, etc.), it is essential that the patient get carefully evaluated to detect these problems and undergo appropriate treatment if the cause can be established. Patients with memory disorders should first undergo a basic evaluation that consists of complete diagnostic interview (including medication and family history), physical examination, magnetic resonance imaging (MRI), and laboratory examination (including electrolyte panel, complete blood count, thyroid function tests, urine analysis, blood urea nitrogen, creatine, vitamin B12, blood tests for masked infections such as HIV or syphilis, and screening for heavy metals or other toxic exposures). Under special circumstances, an EEG or lumbar puncture to collect CSF may be recommended.
Because dementia involves a decline from baseline in multiple cognitive domains, it is important to get a baseline measure of function. In this regard, it is essential to include in the interview anyone who has known the patient and their level of intellectual function for a long time. For example, a patient who has many years of schooling and who has worked in an occupation requiring many mental skills can have minimal symptoms in the presence of very advanced disease. As another example, an aerospace engineer who has mild difficulty balancing the checkbook is not the same as someone with a 7th grade education with the same problem. Also, patients suffering from severe depression can sometimes look severely demented. A simple depression screening test can help exclude this condition (Geriatric Depression Scale). Simple test of mental function used routinely in the memory clinic include the Mini-Mental State Exam or the Montreal Cognitive Assessment.
If following the evaluation above, a diagnosis is not evident, then a neuropsychological evaluation is recommended. Such evaluation can take several hours and examines different aspects of brain function (e.g., language, memory, problem solving, attention, perception) using simple pencil and paper tests, or other tests that can be administered with simple equipment (e.g., peg board, wood blocks, etc.). It is important to realize there is no right or wrong answer; different patients have different strengths and may answer more questions than others. There is no need to feel intimidated by testing. The person interpreting the tests is looking for patterns across the many tests performed.
Once the neuropsychological evaluation is completed, additional tests may be recommended. For example, a PET scan may be requested to visualize any areas of the brain that are not working optimally. Often, a radioactive sugar (fluorodeoxyglucose or FDG) is injected into a vein, and the sugar is taken up by the brain depending on how active it is. This scan can help sort out a particular kind of neurodegenerative disease (e.g., Alzheimer’s disease, AD, from frontotemporal dementia, FTD). Medicare will often cover the cost of the PET scan when the diagnosis is not clear, and all the appropriate testing noted above has been completed. Typically, we find such a scan is helpful only when a computer can compare the individual patient’s brain scan to a reference dataset of scans taken from healthy individuals, both male and female, of a wide range of ages. The software provides a picture of the difference in brain function between the individual patient and the normative group. Thus, if the patient does not differ from healthy subjects in brain function, no “hot spots” (which actually indicate decreases in brain function) arise (see B below). If the patient has areas that do not appear to work as well as the same regions in healthy subjects, then “hot spots” (which actually indicate decreases in brain function) indicate problem areas (see A or C below). Depending on where the problems arise, different types of dementia can be diagnosed more specifically.
For example, the picture below shows examples of individual patients getting evaluated for memory problems at our clinic. All patients were scanned while resting with eyes closed. The scan took about 20 minutes to acquire. The top panel (A) shows a patient with memory problems with a pattern on the PET scan characteristic of early Alzheimer’s disease. The middle panel (B) shows a patient who has minimal changes compared to those found in healthy controls—this is a negative study. A negative study can reassure the patient that there is no gross abnormality in brain function. The bottom panel (C) shows another patient’s PET scan with a pattern found typically in frontotemporal dementia. Depending on the precise diagnosis, the physician may recommend different medications and may provide a prognosis as to what symptoms to expect with time. Such information can be useful in terms of long-term planning.
One new exciting area that is under consideration by the FDA but remains investigational is amyloid imaging. This method also uses a PET scan, but a different radioactive molecule is used to “light up” the amyloid plaques in the brain.
For further information, please go to the Alzheimer’s Association home page http://alz.org/research/overview.asp