Sorting Out the Different Types of Dementia

It’s too easy to think that Alzheimer’s disease is dementia, and all dementias are Alzheimer’s.  It’s not only too easy; it may lead to incorrect treatment.  This is pointed out in three articles in the German medical journal Deutsches Aerzteblatt. 

The first article discusses the early detection of Alzheimer’s before the onset of dementia.  Dementia consists, by definition, of an acquired impairment of memory and cognition that diminishes the sufferer’s ability to cope with activities of daily living and that has been present for at least six months.  Earlier manifestations comprise the condition termed mild cognitive impairment, which can last as long as 5 years until the onset of dementia.  New ‘biomarkers’ – a lower level of amyloid-beta peptide and an increase in (phosphor-)tau - in the spinal fluid can suggest the presence of Alzheimer’s before the onset of dementia.  (These substances make up the plaques and tangles which are seen in brain tissue on necropsy of Alzheimer patients.)  And new ways of analyzing magnetic resonance imaging (MRI) and electroencephalography (EEG) have proved useful in differentiating these types of dementia.

The second article deals with two types of dementia that call for different treatment from that for Alzheimer’s: Lewy body dementia (LBD) and Parkinson’s disease dementia.  The underlying disturbances in both conditions are severe deficits of two neurotransmitting substances, acetylcholine and dopamine.  In both conditions, problems involving movement (motor manifestations) occur.  In LBD, cognitive and/or psychiatric symptoms are the first to appear.  If motor manifestations emerge within one year, dopamine-stimulating treatment should be given.  In Parkinson’s disease, on the other hand, memory impairment and cognitive deficits only appear after the development of motor symptoms has been present for a year; in this case, cholinesterase inhibitors are useful.  Antipsychotic drugs should be avoided in such patients, because of their serious side effects.

Finally, Professor Mahlberg, in his overview of these two papers, lends his support to the use of classical tests (e.g. the Mini-Mental State Exam) for the diagnosis of dementia, and he reminds us that olfactory function (the sense of smell) is easily tested, with little stress to the patient.  He’s enthusiastic about new evaluations of mild cognitive impairment.

Professor Mahlnberg points out that it’s during the first 1/3 of the course of dementia that differential diagnosis –selection of the actual type of dementia – is important, because of the difference in approach suggested in the second article (above).  Later in dementia, the differences are harder to detect, and the situation can be complicated by the overlap of vascular dementia pathology.  Indeed, there are some specialists who believe Alzheimer’s and vascular dementia are not really distinct, but merely represent two poles of a continuum of diseases, which may include LBD and Parkinson’s dementia.  Clearly, there’s plenty of research remaining to be done before we can truly begin to understand the growing epidemic of dementia throughout the world.