There is fairly widespread confusion between the term “dementia” and Alzheimer’s disease. Although it is the most common disorder within this group of disorders associated with pathological cognitive impairment, it is worth clarifying specifically what the differences are between Alzheimer’s disease and the other types of dementia that exist.

In this article we will analyze what distinguishes the most frequent cause of dementia from the three that follow it 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.

Alzheimer’s disease: main features

The DSM-IV defines dementia as a set of cognitive deficits that include significant memory impairment , as well as aphasia, apraxia, agnosia and/or alterations in executive functions, such as planning and sequencing. Although many of the diseases that cause dementia are progressive in nature, this is not always the case.

Dementia due to Alzheimer’s disease is the most common of all. On a physiopathological level it is characterised by the presence of neurofibrillary tangles (conglomerates of tau proteins) and neuritic or senile plaques, 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 with respect 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 the ability to judge is altered, disorientation is markedly aggravated (especially spatial disorientation, which causes affected persons to become lost in the street) and psychotic symptoms such as hallucinations and delusions may appear.

The final phase of Alzheimer’s disease is characterized by, among other signs, autopsy disorientation, lack of recognition of loved ones, complete loss of language and increasing difficulties in walking until walking apraxia. As in many other dementias, in the final phase the affectation 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 following three most common causes of dementia.

1. Vascular dementia

We speak of vascular dementia or multi-infarct when the cerebral – and therefore cognitive – deterioration occurs as a consequence of repeated strokes . It is generally diagnosed in the presence of atherosclerosis, which is defined as a hardening of the arteries that obstructs blood flow.

In these cases, symptoms and signs vary depending on the regions of the brain affected by the heart attack, as well as the intensity of the attack. It is common for the onset to be abrupt, coinciding with a stroke, and then the deterioration to progress in a staggered manner, unlike the linearity of Alzheimer’s.

However, very often vascular dementia occurs simultaneously with Alzheimer’s disease. When this happens we speak of mixed dementia or Alzheimer’s disease with a vascular component . In these cases the signs also vary, but the temporoparietal involvement makes the mnesic symptoms central.

2. Dementia with Lewy bodies

This type of dementia is characterized by the presence of Lewy bodies, structures derived from the degeneration of the proteins of 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 in Alzheimer’s disease.

The most characteristic signs of this type of dementia are visual hallucinations , attentional deficits (which cause sudden fits of confusion), alterations in executive functions and parkinsonian symptoms such as rigidity and tremors at rest. The deterioration of memory is less severe than in the case of Alzheimer’s.

Another relevant difference between Lewy’s disease and Alzheimer’s disease 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

This term includes primary progressive aphasia and semantic dementia . Fronto-temporal dementias begin with involvement of the frontal and/or temporal lobes; sometimes the frontal lobe is injured 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 stages. In contrast, language 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 synthesised , which causes neurofibrillary tangles similar to those in Alzheimer’s disease. However, neuritic plaques are absent. Both physiopathological features also characterize dementia due to Creutzfeldt-Jakob disease.