There is widespread confusion between the term “dementia” and Alzheimer’s disease. Although it is the most common within this group of disorders associated with pathological cognitive impairment, it is worth clarifying specifically what the conditions are. differences between Alzheimer’s disease and the other types of dementia that exist.
In this article we will analyze what distinguishes the most common cause of dementia from the three that follow in prevalence: vascular dementia, dementia with Lewy bodies and frontotemporal dementias. A fourth very common type is mixed dementia, which combines the signs of Alzheimer’s with those of vascular dementia.
The DSM-IV defines dementia as a set of cognitive deficits including significant memory impairment, in addition to aphasia, apraxia, agnosia and/or alterations in executive functions, such as planning and sequencing. Although many of the diseases that cause dementia are progressive, this is not always the case.
Dementia due to Alzheimer’s disease is the most common of all. At a pathophysiological level, it is characterized by presence of neurofibrillary tangles (conglomerates of tau proteins) and neuritic plaques or senile, deposits of beta-amyloid peptides whose presence is associated with neuronal degeneration and hyperproliferation of glial cells.
From a symptomatic point of view, the main peculiarity of Alzheimer’s disease compared to other causes of dementia is that it begins by affecting the temporal and parietal lobes of the brain. This explains the initial signs of Alzheimer’s: learning and recent memory problems, personality changes, and depressive symptoms.
Cognitive impairment continues to progress irreversibly. Between 3 and 5 years after the onset of the disease judgment is impaired, disorientation becomes noticeably worse (especially spatial, which causes affected people to get lost on the street) and psychotic symptoms such as hallucinations and delusions may appear.
The final phase of Alzheimer’s disease is characterized, among other signs, by self-psychic disorientation, lack of recognition by loved ones, complete loss of language and increasing difficulties in walking until reaching gait apraxia. As in many other dementias, In the final phase the impact is global and causes death.
Differences between Alzheimer’s and other dementias
Below we will describe the main characteristics that distinguish Alzheimer’s disease from the next three most common causes of dementia.
1. Vascular dementia
We speak of vascular dementia or multi-infarction when the brain deterioration – and therefore cognitive – occurs as consequence of repeated strokes. It is usually diagnosed in the presence of arteriosclerosis, which is defined as a hardening of the arteries that obstructs blood flow.
In these cases, the symptoms and signs vary depending on the regions of the brain that are affected by the heart attacks, as well as their intensity. It is common for the onset to be abrupt, coinciding with a stroke, and for the deterioration to subsequently progress in a gradual manner, unlike the linearity typical of Alzheimer’s.
However, vascular dementia very often occurs simultaneously with Alzheimer’s disease. When this happens we talk about mixed dementia or Alzheimer’s disease with vascular component. In these cases the signs also vary, but the temporoparietal involvement makes the mnesic symptoms central.
This type of dementia is characterized by the presence of Lewy bodies, structures derived from the degeneration of proteins in the cellular cytoplasm, in the frontal, parietal and temporal cortex of the brain, as well as in the substantia nigra. Neuritic plaques of beta-amyloid protein are also found, as occurs in Alzheimer’s.
The most characteristic signs of this type of dementia are visual hallucinations, attention deficits (which cause sudden bouts of confusion), alterations in executive functions and parkinsonian symptoms such as rigidity and rest tremors. Memory impairment is less severe than in the case of Alzheimer’s.
Another relevant difference between Lewy’s disease and Alzheimer’s is the fact that in the former there is a deficit in the levels of the neurotransmitter dopamine. This characteristic largely explains the similarity of this disorder with Parkinson’s disease.
3. Frontotemporal dementias
That term includes primary progressive aphasia and semantic dementia. Frontotemporal dementias begin with involvement in the frontal and/or temporal lobes; Sometimes the frontal lobe is damaged from the beginning in Alzheimer’s disease (and in particular the limbic region, associated with emotions), but this is not always the case.
In these dementias the memory impairment is less obvious than in those due to Alzheimer’s disease, especially during the initial phases. On the other hand, linguistic problems and behavioral disinhibition are more pronounced in this group of disorders.
Frontotemporal dementias are associated with mutations in the gene from which the tau protein is synthesized, which causes neurofibrillary tangles similar to those of Alzheimer’s. However, neuritic plaques are absent. Both pathophysiological features also characterize dementia due to Creutzfeldt-Jakob disease.
