The differences between Parkinson’s disease and Alzheimer’s disease

Parkinson’s and Alzheimer’s disease, respectively, are the causes of two common types of neurological disorders associated with dementia.

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

    Differences between disease and dementia

    We need to be aware of the differences between illness and dementia because illness 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 result of injury or neurological disease.

    Parkinson’s disease, on the other hand, doesn’t always lead to dementia (Yes, this is the case in 20 to 60% of cases); In contrast, Alzheimer’s disease usually always leads to dementia (and at an early stage).

    Differences between Parkinson’s disease and Alzheimer’s disease

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

    1. Dementia

    In Alzheimer’s disease, dementia appears early and attention and memory are particularly affected. however, in Parkinson’s disease, if dementia does appear, it does so later.

    In contrast, Alzheimer’s dementia is cortical (affecting the cerebral cortex) and Parkinson’s dementia is subcortical (affecting subcortical areas).

    Generally speaking, cortical dementias involve cognitive impairments and subcortical dementias, motor disorders.

    2. Other symptoms

    In Alzheimer’s disease, delirium occurs occasionally, and in Parkinson’s disease, it occurs less often.

    In Alzheimer’s disease and Parkinson’s disease, visual hallucinations can sometimes appear. On another side, in Alzheimer’s disease, they appear a delirium of typical form, And in Parkinson’s disease, they only appear occasionally.

      3. Motor symptoms

      parkinsonism (The clinical syndrome characterized by tremors, bradykinesia, stiffness and postural instability) is the first manifestation of Parkinson’s disease; on the contrary, this symptom is rare in Alzheimer’s disease.

      In the same way, stiffness and bradykinesia usually appear in Parkinson’s disease, And sometimes in Alzheimer’s disease.

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

        4. Cognitive symptoms

        In Parkinson’s disease there are retrieval errors and in Alzheimer’s disease there are coding (memory) errors.

        5. Pathological signs

        Senile plaques in the brain they usually appear in Alzheimer’s disease, although rarely in Parkinson’s disease. Likewise, neurofibrillary tangles usually appear in Alzheimer’s disease, but rarely in Parkinson’s disease.

        Lewy cortical bodies rarely appear in Alzheimer’s disease and more often in Parkinson’s disease (occasionally). Subcorticals, on the other hand, are typical of Parkinson’s disease and rare in Alzheimer’s disease.

        On another side, acetylcholine deficiency it is typical of Alzheimer’s disease and occasional of Parkinson’s disease. Finally, the reduction in dopamine only appears in Parkinson’s disease.

        6. Age of onset and prevalence

        Finally, following the differences between Parkinson’s disease and Alzheimer’s disease, we know that Parkinson’s disease appears before Alzheimer’s disease (at the age of 50-60 years), while Alzheimer’s disease usually appears a little later, from the age of 65.

        On the other hand, in terms of dementia, the prevalence of dementia for Alzheimer’s disease is higher (It is the leading cause of dementia), and it is 5.5% in Spain and 6.4% in Europe.

        Symptoms of Alzheimer’s disease and Parkinson’s disease

        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 manifested by cognitive impairment (Dementia), behavioral and emotional disturbances. When it causes dementia and according to DSM-5, it is called major or mild neurocognitive disorder due to Alzheimer’s disease.

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

        1.1. first phase

        The first changes appear and this lasts between 2 and 4 years. Anterograde amnesia manifests itself (Inability to create new memories), mood and personality changes, as well as impoverished language (anomias, circumlocutions and paraphrases).

        1.2. Second level

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

        The patient is already unable to live unattended and has spatio-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 stage of the disease. Here appears autopsychic disorientation and that of others, as well as silence and an inability to perform basic activities of daily living (ABVD) such as eating or bathing.

        Alterations in the gait also appear (the “gait is done in small steps”). On another side, Kluver Bucy’s syndrome can manifest itself; it is a syndrome in which there is a lack of fear of stimuli that should generate, a lack of risk assessment, gentleness and obedience alongside blind hypersexuality and overeating, among others.

        Finally, at this stage, the patient ends up lying down, characteristic with the adoption of a fetal posture.

        2. Parkinson’s

        Parkinson’s disease is a chronic neurodegenerative disease characterized by different motor disorders such as bradykinesia, stiffness, tremors and loss of postural control.

        Between 20 and 60% of patients with Parkinson’s disease develop Parkinson’s dementia (cognitive impairment). This dementia, DSM-5, is called a major or mild neurocognitive disorder due to Parkinson’s disease.

        Once dementia appears, the symptoms consist of: errors in memory recovery processes, decreased motivation (apathy, asthenia and abulia), bradypsychia (slowing down the thought process) and impoverishment of language. Bradykinesia (slowness of movement) also occurs, although aphasia-apraxo-agnosic syndrome does not appear as in Alzheimer’s dementia.

        Visuospatial and visoconstructive alterations also appearAnd finally, Parkinson’s disease is strongly linked to depression.

        In contrast, it is common in Parkinson’s dementia the presence of dysexecutive syndrome (Alteration of the prefrontal lobe).


        As we have seen, the differences between Parkinson’s disease and Alzheimer’s disease are remarkable, although they share many other characteristics. for that it is important to make a good differential diagnosisIn order to be able to carry out a treatment adapted to each case and patient.

        Bibliographical references:

        • Belloch, A .; Sandín, 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.

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