Parkinson’s disease and Alzheimer’s disease, respectively, are the causes of two common types of neurological disorders related to dementias.

However, there are many aspects that allow us to distinguish between the two diseases; in this article we will know the most important differences between Parkinson’s disease and Alzheimer’s .

Differences between disease and dementia

We must be aware of the differences between disease and dementia, as the disease does not always lead to dementia (cognitive impairment), 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, on the other hand, does not always lead to dementia (it does in 20-60% of the cases); on the other hand, Alzheimer’s disease always leads to dementia (and early on).

Differences between Parkinson’s and Alzheimer’s disease

As for the differential diagnosis between Parkinson’s and Alzheimer’s diseases, we found several differences in their presentation. We will see them in different blocks:

1. Dementia

In Alzheimer’s, dementia appears early, and attention and memory are especially affected. In contrast, 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 involve cognitive alterations, and subcortical dementias involve 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 occur. On the other hand, in Alzheimer’s disease, delusions typically appear , and in Parkinson’s disease they appear only occasionally.

3. Motor symptoms

Parkinsonism (a clinical syndrome characterized by tremor, bradykinesia, rigidity, and postural instability) is the first manifestation of Parkinson’s; in contrast, this symptom is rare in Alzheimer’s.

Similarly, rigidity and bradykinesia typically appear in Parkinson’s , and occasionally in Alzheimer’s.

Tremor is typical in Parkinson’s and rare in Alzheimer’s.

4. Cognitive symptoms

In Parkinson’s disease there are failures in recovery, and in Alzheimer’s disease there are failures in coding (memory).

5. Pathological signs

Senile plaques in the brain 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). Subcorticals, on the other hand, are typical in Parkinson’s and rare in Alzheimer’s.

On the other hand, the deficit in acetylcholine is typical in Alzheimer’s and occasional in Parkinson’s. Finally, the reduction in dopamine 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 of age), while Alzheimer’s usually appears a little later, from 65 years of age onwards.

On the other hand, in terms of 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 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 that manifests itself as cognitive impairment (dementia), behavioural 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.

The symptoms of Alzheimer’s 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. Antegrade amnesia (inability to create new memories), changes in mood and personality, as well as impoverished language (anomie, circumlocution and parafasia) appear.

1.2. Second phase

In this phase the deterioration continues (it lasts between 3 and 5 years). The aphaso-apraxo-agnostic syndrome appears, as well as retrograde amnesia and a deterioration in the capacity for judgment, and alterations in abstract thinking. Instrumental activities of daily living (IADL), such as shopping or calling the plumber, are already affected.

The patient is already incapable of living without supervision, and presents a spatial-temporal disorientation .

1.3. Third phase

In this last phase the deterioration is already very intense, and the duration is variable. This is the advanced phase of the disease. Here appears an autopsy and other people’s disorientation, as well as mutism and the impossibility to perform basic activities of daily living (ABVD) such as eating or grooming.

There is also a change of pace (the “small steps”). On the other hand, the Kluver Bucy Syndrome can be manifested; it is a syndrome in which a lack of fear appears before stimuli that should generate it, absence of risk assessment, meekness and obedience together with indiscriminate hypersexuality and hyperphagia, among others.

Finally, in this phase the patient ends up in bed, characteristically with the adoption of a fetal posture.

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 impairment). 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 abulia), bradypsychia (slowing down of the thinking 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 visoconstructive 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 the dysexecutive syndrome (alteration of the prefrontal lobe).


As we have seen, the differences between Parkinson’s disease and Alzheimer’s are remarkable, although they share many other characteristics. For this reason 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. Panamericana.