The differences between Parkinson's disease and Alzheimer's

Parkinson's and Alzheimer's diseases, respectively, are the causes of two common types of dementia-related neurological disorders.

However, there are many aspects that make it possible to distinguish between one disease and another; in this article we will know the most important differences between Parkinson's disease and Alzheimer's.

• Related article: "Types of dementias: the 8 forms of loss of cognition"

Differences between disease and dementia

We must be aware of the differences between disease and dementia, since the disease does not always lead to dementia (cognitive alterations), although it usually does.

Thus, the term dementia refers to a set of symptoms that appear as a consequence of neurological damage or disease.

Parkinson's disease, meanwhile, does not always lead to dementia (it does in 20-60% of cases); On the other hand, Alzheimer's disease does usually always lead to dementia (and early).

Differences between Parkinson's disease and Alzheimer's

Regarding the differential diagnosis between Parkinson's and Alzheimer's diseases, we found several differences in terms of their presentation. We will see them in different blocks:

1. Dementia

In Alzheimer's, dementia appears early, and attention and memory are especially affected. Instead, in Parkinson's, if dementia appears, it does so later.

On the other hand, Alzheimer's dementia is cortical (involvement of the cerebral cortex), and Parkinson's dementia is subcortical (involvement of subcortical areas).

Broadly speaking, cortical dementias imply cognitive alterations, and subcortical dementias, motor alterations.

2. other symptoms

In Alzheimer's disease, delirium appears occasionally, and in Parkinson's this occurs less often.

In both Alzheimer's and Parkinson's, visual hallucinations may occasionally appear. On the other hand, delusions typically appear in Alzheimer's, and in Parkinson's they appear only occasionally.

• You may be interested in: "The 15 types of hallucinations (and their possible causes)"

3. motor symptoms

parkinsonism (clinical syndrome characterized by tremor, bradykinesia, rigidity, and postural instability) is the first manifestation of Parkinson's; instead, this symptom is rare to appear in Alzheimer's.

The same way, rigidity and bradykinesia are typical in Parkinson's, and occasionally in Alzheimer's.

The tremor is typical in Parkinson's and rare in Alzheimer's.

• You may be interested in: "Parkinson's: causes, symptoms, treatment and prevention"

4. cognitive symptoms

In Parkinson's there are failures in recovery, and in Alzheimer's failures in encoding (memory).

5. pathological signs

senile plaques in the brain They appear typically in Alzheimer's, although rarely in Parkinson's. Similarly, neurofibrillary tangles also typically appear in Alzheimer's, but rarely in Parkinson's.

Cortical Lewy bodies appear rarely in Alzheimer's and more often in Parkinson's (occasionally). The subcortical ones, on the other hand, are typical in Parkinson's and rare in Alzheimer's.

On the other hand, acetylcholine deficiency it is typical in Alzheimer's and occasional in Parkinson's. Finally, dopamine reduction appears only in Parkinson's.

6. Age of onset and prevalence

Finally, continuing with the differences between Parkinson's disease and Alzheimer's, we know that Parkinson's appears before Alzheimer's (at 50-60 years), while Alzheimer's usually appears a little later, after 65 years.

On the other hand, regarding dementias, the prevalence of Alzheimer's dementia is higher (it is the first cause of dementia), and this is 5.5% in Spain and 6.4% in Europe.

Symptoms in Alzheimer's and Parkinson's

Now that we have seen the differences between Parkinson's disease and Alzheimer's disease, let's learn more about the symptoms of each of these diseases:

1. Alzheimer's

Alzheimer's disease is a neurodegenerative disease manifesting as cognitive impairment (dementia), behavioral disorders and emotional disorders. When it leads to dementia and according to the DSM-5, it is called Major or Mild Neurocognitive Disorder Due to Alzheimer's Disease.

Alzheimer's symptoms change as the disease progresses. We can differentiate three types of symptoms according to the three phases of Alzheimer's:

1.1. First phase

The first deterioration appears and lasts between 2 and 4 years. Anterograde amnesia manifests (inability to create new memories), changes in mood and personality, as well as impoverished language (anomies, circumlocutions, and paraphasias).

1.2. Second stage

In this phase the deterioration continues (lasts between 3 and 5 years). The afaso-apraxo-agnosic syndrome appears, retrograde amnesia and impaired judgment, as well as alterations in abstract thinking. Instrumental activities of daily living (AIVD) such as going shopping or calling the plumber are already affected.

The patient is no longer incapable of living without supervision, and presents a spatiotemporal disorientation.

1.3. Third phase

In this last phase the deterioration is already very intense, and the duration is variable. It is the advanced stage of the disease. Here appears a self-psychic disorientation and that of the rest of the people, as well as mutism and the impossibility of carrying out the basic activities of daily living (ABVD) such as eating or cleaning oneself.

Gait disturbances also appear (the "walk in small steps" occurs). On the other hand, Kluver Bucy Syndrome can manifest; It is a syndrome in which there is a lack of fear in the face of stimuli that should generate it, an absence of risk assessment, meekness and obedience together with indiscriminate hypersexuality and hyperphagia, among others.

Finally, in this phase the patient ends up bedridden, characteristically adopting a fetal position.

2. Parkinson's

Parkinson's is a chronic neurodegenerative disease, characterized by different motor disorders such as bradykinesia, rigidity, tremor, and loss of postural control.

Between 20 and 60% of patients with Parkinson's disease develop Parkinson's dementia (cognitive alterations). DSM-5 calls this dementia Major or Mild Neurocognitive Disorder Due to Parkinson's Disease.

Once dementia appears, the symptoms consist of: failures in memory recovery processes, decreased motivation (apathy, asthenia and avolition), bradypsychia (slowing of the thought process) and impoverishment of language. Bradykinesia (slowness of movement) also appears, although the aphaso-apraxo-agnostic syndrome does not appear as in Alzheimer's dementia.

Visuospatial and visuoconstructive alterations also appear, and finally, Parkinson's is strongly related to depression.

On the other hand, it is common in Parkinson's dementia the presence of dysexecutive syndrome (alteration of the prefrontal lobe).

Conclusion

As we have seen, the differences between Parkinson's disease and Alzheimer's are notable, although they share many other characteristics. That's why it is important to make a good differential diagnosis, in order to be able to carry out an adequate treatment for each case and patient.

Bibliographic references:

• Belloch, A.; Sandin, b. And Ramos, F. (2010). Manual of Psychopathology. Volume II. Madrid: McGraw-Hill
• APA (2014). DSM-5. Diagnostic and Statistical Manual of Mental Disorders. Madrid. Pan American.