Parkinson's Disease: Moving ForwardPage 10 of 17

8. Cognitive Changes in Parkinson’s Disease

In recent years, there has been increasing interest in cognitive and behavioral changes associated with Parkinson’s disease. Recent studies have identified deficits in cognitive function, neuropsychiatric status, and language. There has been a parallel development in the domain of speech, as researchers have turned from a focus purely on speech production deficits to an interest in possible deficits of speech perception (Kwan & Whitehill, 2011).

Cognitive and behavioral symptoms can appear at the earliest stages of the Parkinson’s, before any treatment has occurred, and may even be biomarkers for PD. Cognitive profiles are variable and range from mild deficits in specific cognitive domains to severe dementia affecting multiple domains. It is estimated that 19% to 30% of people with early, newly diagnosed PD present with cognitive impairments and these impairments worsen with disease progression (Kelly et al., 2012).

Mild Cognitive Impairment and Dementia

Cognitive impairment and the development of dementia are increasingly being considered part of the course of Parkinson’s disease. Of particular importance, nearly 90% of PD patients with dementia exhibit at least one neuropsychiatric symptom, and 77% have two or more neuropsychiatric symptoms. Risk factors for the development of mild cognitive impairment include older age at disease onset, male gender, depression, severity of motor symptoms, and advanced disease stage (Leroi et al., 2012).

The prevalence of dementia in PD is estimated at 26% to 44%, with over 80% developing dementia within 20 years of diagnosis. Mild cognitive impairment (MCI) in people with PD is associated with the development of dementia within 4 years (Kelly et al., 2012). Depression can exacerbate cognitive impairments in PD, and the frequency of depression in PD is estimated at 25% to 33% (Kelly et al., 2012).

In a study that examined clusters of neuropsychiatric symptoms and cognitive status in PD, it was found that in people suffering from hallucinations nearly 80% had dementia; in those with mixed neuropsychiatric symptoms nearly 58% had dementia; and in those with mild depression 31% had dementia. Patients experiencing hallucinations tended to have longer disease duration, more severe motor symptoms, and older age (Leroi et al., 2012).

Mood Alterations

Mood alterations such as depression, anxiety, and apathy are increasingly being thought of as a component of PD. Supporting this theory are findings of alterations in the serotonergic signaling pathways. As with sleep disorders, constipation, and olfactory disruption, anxiety and depression are nonspecific and do not stand alone as clinical premotor PD biomarkers (Haas et al., 2012).


The most frequently experienced and researched psychological difficulty in people with PD is depression. Some researcher has demonstrated that the pattern of depression varied in a nonlinear way over the course of PD and suggested that depression is not simply a result of increasing impairment. Other studies have suggested that disability and participants’ perceptions of the personal and social impact of PD were stronger predictors of depression than impairment (Simpson et al., 2013).

Depression is detected in nearly a quarter of patients in the early stages of PD. Several groups have indicated that in the later stages of PD depression rates are approximately 40%, but that this rate is probably grossly underestimated (Haas et al., 2012). Depression and anxiety tend to be more frequent during medication off-periods and often improve when the dopaminergic treatment is optimized (Lokk & Delbari, 2012).

Antidepressants—especially serotonin reuptake inhibitors (SSRIs)—are widely used to treat PD patients with depression. Other drugs are less advisable because they carry more risk of cognitive side effects, which is especially true for tricyclic antidepressants (Lokk & Delbari, 2012).


Two-thirds of PD patients with motor fluctuations experience anxiety, often associated with irritability (Lokk & Delbari, 2012). Some researchers have even speculated about a possible “parkinsonian personality” that involves such traits as inflexibility, neuroticism, obsessive-compulsivity, uneasiness, and anxiety, among others. These characteristics may be present from childhood, leading to the possibility of long lasting biologic changes preceding PD motor symptoms, and possibly implying that the observed motor symptoms of PD are really characteristic of end-stage disease (Haas et al., 2012).


The behavioral syndromes of apathy and impulse control disorders, and the symptoms that comprise them, have received much less attention and are less well understood than cognitive impairment and dementia (Ahearn et al., 2012).

Apathy is defined as a lack of goal-directed behavior, cognition, or emotion. It is closely linked to cognitive impairment and may even be a harbinger of conversion to dementia. A recent longitudinal study of a PD cohort without dementia found that after a median period of 18 months, the proportion of those who converted to dementia was significantly higher in those with apathy. In those who did not develop dementia, cognitive decline was still greater in the apathy sufferers (Leroi et al., 2012).

The Psychosocial Impact of Stigma

Several studies have found correlations between perceived stigma and depression in people with PD. Participants in qualitative studies have repeatedly reported embarrassment and shame about having PD. From a social relations perspective, it is argued that these feelings are, in part, a result of stigmatizing attitudes and actions of other people because PD is seen as breaking social rules. The shame experienced by people with PD can be considered “public shame,” with their home and private world being experienced as safer, which highlights the social relational nature of shame (Simpson et al., 2013).

The socially created shame about having PD may be internalized and taken on as part of a person’s self-identity. Some qualitative studies have explored the concept of self-identity in PD, and participants have described the challenges of living with PD and how it affects their sense of self and their social roles. People with chronic illness may feel discredited, which can be influenced by stigmatizing and disabling societal views of illness (Simpson et al., 2013).

A person may internalize the negative stereotypes of what it means to have PD. This may be particularly pertinent for people who acquired impairments as adults after they had earlier developed perceptions of impairment from a non-impaired perspective. They may impose their own non-impaired view of illness on themselves. For example, a person with PD may experience negative feelings about being a burden and strive to sustain independence (Simpson et al., 2013).

Changes in Social Contact

Changes in social contact are reported by many people with PD. In some studies, participants described choosing to spend time with people who were in a similar position to them rather than people without PD or impairment. Other people’s lacking understanding or being uncomfortable with PD have been cited as a contributory factor to altered social contacts. People who have Parkinson’s disease have reported benefits from spending time with other people with PD in nonstigmatizing contexts such as self-help and therapeutic groups. Moreover, studies have found that people with PD and their families often avoid social situations due to fear of negative judgment by others. As such, negative and stigmatizing public attitudes or action by others are considered to limit social opportunities for people with PD (Simpson et al., 2013).

Negative social experiences can contribute to psychological difficulties. For example, social rejection and reduced social contact have been found to be associated with depression in people with PD. Experiencing psychological difficulties may further fuel the stigma associated with PD, since mental health difficulties in themselves have been found to be stigmatizing. People with PD have reported being reluctant to take medication or engage in psychological therapy for depression because of the additional stigma associated with perceived mental health problems (Simpson et al., 2013).

The Stigma of Impaired Communication

People who have Parkinson’s may be subject to negative actions and stigmatizing attitudes about their communication style. For example, there may be misunderstanding and lack of awareness about speech or expressive masking, reduced facial, body, and vocal expressions due to muscular difficulties. People with PD have been perceived by others as being less sociable, less happy, and less friendly due to their speech style and facial masking. Some aspects of personality (e.g., extroversion, neuroticism) in people with facial masking are often inaccurately perceived by professionals, particularly by novice professionals. Furthermore, studies have found that caregivers can often misinterpret how people with PD are feeling (Simpson et al., 2013).

Misinterpretation and inaccurate judgment about a person’s character or feelings may affect social interactions. This may emotionally impact the person with PD. However, more experienced professionals were found to be less likely to misinterpret neuroticism than novice professionals, suggesting that experience and awareness of PD contributes to more accurate perceptions. Accordingly, raising public awareness about the lesser known features of PD, such as facial masking, may help reduce negative or misinformed perceptions (Simpson et al., 2013).