Dementias involve a progressive loss of cognitive functions (memory, attention, language…) and adaptive abilities. They can originate from different causes, generally organic. Their progression ends up causing the patient an inability to carry out the activities of daily life. However, what types of dementia exist? How do they all differ from each other?
In this article, we’ll learn about the clinical-anatomical classification of dementias. Furthermore, we’ll list the dementias in each group and describe some of the most important. The most well-known types of dementia are Alzheimer’s and Parkinson’s (with Alzheimer’s being the first cause of dementia), although there are many more.
Types of dementia
We found an extremely useful and complete clinical-anatomical classification of dementias, which groups them according to their location and neuroanatomy.
1. Localized dementias
Localized dementias, as their name suggests, are located in a certain brain area. They consist of the following.
1.1. Cortical dementia
Its central feature is cognitive impairment (more predominant than in subcortical types of dementia). The following dementias belong to this group:
- Alzheimer’s dementia.
- Frontotemporal dementia (Pick).
- Creuzfeldt-Jakob Disease.
- Lewy body dementia.
At the level of brain chemistry, cortical dementias are characterized by a decrease in the following substances: acetylcholine (Ach) and dopamine (DA).
1.2. Subcortical dementia
Unlike the previous types, motor alteration predominates in subcortical dementias. They’re dementias that typically present with motor slowing, bradypsychia (mental slowness), and decreased motivation. This last symptom translates into apathy, asthenia, and abulia. Subcortical dementias are:
- Parkinson’s dementia.
- Huntington’s dementia.
- HIV- associated dementia.
At the neurochemical level, in this type of dementia there’s a decrease in the following neurotransmitters: dopamine (DA) and GABA.
1.3. Axial dementias
The best known axial dementia is Korsakoff syndrome. Memory is particularly impaired in this type of dementia. In addition, patients with Korsakoff suffer from anosognosia. This implies the absence of perception of deficits. In other words, patients are unaware of the disease.
2. Global dementias
Global dementias are also called vascular or mixed dementias. Sometimes, they result from a heart attack. This type of dementia is characterized by the following:
- They’re heterogeneous. In other words, they present symptoms that are different from each other.
- The cognitive impairment that appears is extremely broad.
- They follow a graduated course, subject to fluctuations.
- They’re treatable.
Global dementias include mainly cognitive symptoms, as well as emotional lability, confusion, depression, urinary incontinence, etc. Their onset is abrupt and the deterioration they produce is irregular.
On the other hand, there’s usually a small element of recovery in them. The population at risk that can suffer from these types are people with a history of CVA (cerebrovascular accidents), people with hypertension, etc.
3. Other types of dementia
In this final section, we find the kinds of dementia that can’t be classified in the previous groups. They include the dementias produced by traumatic brain injury (TBI), medication or substances, or other medical conditions. In fact, they’re dementias that occur due to multiple causes (with multiple etiologies).
Types of cortical dementia
We’re now going to see in more detail what characterizes some of the most important dementias of the cortical group.
Alzheimer’s dementia was first described by the German psychiatrist and neurologist, Alois Alzheimer (1864-1915), in the early 1900s. This dementia has a gradual onset, with continuous, joint, homogeneous, and uniform deterioration. According to the DSM-5, the median survival after diagnosis is ten years. It can progress rapidly (two-four years) or slowly (15 years).
Alzheimer’s is the most frequent kind of dementia. According to the DSM-IV-TR, it represents 55-65 percent of all cases, although Belloch  suggests 35 percent. The DSM-5 claims that its prevalence in Europe is 6.4 percent. The risk of Alzheimer’s increases dramatically with age.
At the neuropsychological level, Alzheimer’s is the only kind of dementia that debuts with an affection of the medial temporal regions (related to memory). The person with this type of dementia will present symptoms that affect their language, communication skills, memory, and adaptive skills. In fact, they gradually lose all these skills.
Frontotemporal dementia (Pick’s disease)
The most frequent frontotemporal dementia is that caused by Pick’s disease. It was first diagnosed at the end of the 19th century by the Czech psychiatrist, Arnold Pick (1851-1924). Its exact etiology is unknown although it’s related to alterations in tau protein (one of those that maintains the neuronal skeleton).
As a matter of fact, mutations have been found in the gene that encodes this kind of protein, located on chromosome 17 and 3. On the other hand, most frontotemporal dementias are inherited by autosomal dominant inheritance.
McKhann et al (2001) suggest as diagnostic criteria for frontotemporal dementia: cognitive defects in personality (lack of behavioral control, affectivity problems) or language (expression or understanding). Its symptomatology is gradual, with an affectation in daily functioning.
Types of subcortical dementia
Now, we’re going to take a look at the most important types of subcortical dementia:
Not all people with Parkinson’s disease end up developing dementia, although many of them do. Its etiology is unknown, although it’s related to an alteration in the nigrostriatal fasciculus (decreased dopaminergic functioning).
According to the DSM-IV-TR, the so-called dysexecutive syndrome appears in this dementia, linked to memory loss. There’s also a decrease in motivation, bradypsychia, and impoverishment of language, as well as bradykinesia (slowness of movement). However, the aphaso-apraxo-agnosic syndrome, which occurs in Alzheimer’s, doesn’t appear. Visuospatial and visuoconstructive alterations occur, and it’s frequently associated with depression.
Its onset is insidious, and it appears early, between 30-40 years (although the disease that causes it can appear at any age). Its evolution is slow and progressive and its average duration is 15 years. The characteristic symptoms of Huntington’s dementia are:
- Cognitive impairment: early prefrontal dysfunction, visuospatial alterations, bradypsychia, memory alterations.
- Behavioral alterations: withdrawal, apathy, a tendency to silence, depression (although bipolarity may also appear), etc.
- Motor disorder (chorea).
Regarding its etiology, the cause is Huntington’s disease, with autosomal dominant inheritance (chromosome 4). In addition, it causes a significant reduction in GABA levels in the caudate and putamen. It affects men and women equally, and its prevalence is 8/100,000.
“Age is not how old you are, but how many years of fun you’ve had.”
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