An academic research paper analyzing Parkinson’s Disease cognitive impairment, detailing its impact on memory, attention, executive function, language, and visuospatial skills. The paper explores mild cognitive impairment, dementia prevalence, diagnostic challenges, and the necessity for further research to enhance clinical diagnosis and treatment approaches for patients.

Parkinson’s Disease and Cognitive Impairment: A Detailed Study

Parkinson’s disease, also referred to as paralysis agitans, is a progressive neurodegenerative disease leading to movement disorder. The condition currently affects about one million people in the US. It affects men and women equally and results from losing pigmented neurons in the substantia nigra, leading to less production of dopamine (Aarsland et al., 2021). People suffering from the disorder tend to exhibit rigidity, tremors, postural instability, and bradykinesia. Additionally, the disease leads to mild cognitive impairment. Cognition refers to the mental process or action of acquiring knowledge and understanding through experience, thought, and sense. Parkinson’s disease tends to impair cognition leading people to feel disorganized or distracted; and find it difficult to plan and execute duties (Goldman & Sieg, 2020). The objective of this study is to develop an understanding of Parkinson’s Disease how it impacts memory and cognition, and why there should be more research in the field to help in clinical diagnosis in individuals with cognitive impairment.

Overview of Parkinson’s Disease

Parkinson’s Disease results from a reduction in the production of dopamine. Dopamine is a neurotransmitter whose role ranges from ‘reward center’ to movement, memory, mood, motivation, attention, and other body functions (Baiano et al., 2020). Development of Parkinson’s Disease is associated with rigidity, tremors, akinesia, and a gait disorder indicated by short and shuffling steps, and a flexed posture. Diagnosis of the condition is clinically made by detecting at least two of these characteristic motor signs as well as a clear-cut response to antiparkinsonian drugs (Aarsland et al., 2021). According to Baiano et al. (2020), some patients also exhibit freezing and postural instability, which can lead to a sudden inability to initiate or continue movement. In the later stages of the disorder, motor complications such as an ‘on-off’ period and drug-induced involuntary movements take place. Thus, Parkinson’s Disease is as a result of issues with neurotransmission, and causes numerous motor impairments used in clinical diagnosis.

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Impairment Associated with Parkinson’s Disease

Patients with Parkinson’s also experience non-motor symptoms. Depression is experienced in about 50% of the patients suffering from the disease and can occur at any stage in the course of the disease. Patients can also experience visual and rarely auditory hallucinations after taking antiparkinsonian medication for years. According to Baiano et al. (2020), the onset of dementia does not occur in early idiopathic Parkinson’s Disease but tends to develop in later stages. Other symptoms associated with the disorder include frequent urination, difficulty with articulation, autonomic insufficiency, seborrhea, constipation, dysphagia, and ill-defined sensory complaints usually reported as deep aching feelings that in some individuals may be quite painful (Baiano et al., 2020). Parkinson’s disease mostly occurs in older adults, but it is not uncommon among young adults and in very rare cases it can occur in juveniles. Dystonic symptoms are more common among younger patients, with 15% of cases being familial. Therefore, non-motor symptoms are an essential aspect of Parkinson’s Disease as they affect a majority of the patients as they get older.

Cognitive Impairment

Cognition is a mental process that allows individuals to perform their daily functions. This can include solving problems, paying attention, and remembering where things are and how to perform certain tasks (Goldman & Sieg, 2020). Memory is a single aspect of cognition. Other domains include attention and working memory, executive function, language, and visuospatial function.

Attention and Working Memory

Firstly, Parkinson’s Disease affects attention and working memory. Attention refers to the ability to focus selectively on a given aspect of one’s surroundings, usually while ignoring competing stimuli. Patients suffering from Parkinson’s Disease suffer from difficulty concentrating on reading a book or concentrating on a conversation. It may also be difficult for them to walk while maintaining balance. According to Baiano et al. (2020), working memory refers to the memory processing of temporarily stored information and manipulating it over a short period such as mental arithmetic. The cognitive processes are usually linked to alertness. Sedating and sleeping medication can impair attention and the function of working memory. Therefore, attention and working memory are key in clinical diagnosis of the disease.

Executive Function

Secondly, Parkinson’s Disease affects executive function. The domain of cognition entails the ability to organize, plan, regulate, and initiate goal-directed behavior. For instance, leading a company entails multitasking such as problem-solving, switching tasks, and starting new tasks (Aarsland et al., 2021). Parkinson’s Disease affects executive function in the prefrontal cortex and the dopamine system. Executive dysfunction is very common among individuals with the disorder. According to Baiano et al. (2020), the concept of memory involves remembering and learning information. Memory is classified into different types and processes. There is immediate memory, short-term, and long-term memory. There is also memory for concepts, facts, or events referred to as declarative memory and there is a memory for how to perform given tasks such as riding a bicycle, as well as the working memory. People with Parkinson’s disorder may have trouble recalling information, however, in general memory is slightly impaired in Parkinson’s disorder compared to Alzheimer’s Disease (Aarsland et al., 2021). In this disorder, people often recall information readily when given choices or cues, which help individuals retrieve information from memory storage. Long-term memory function tends to remain intact in the disorder. Therefore, executive function is critical in diagnosis of Parkinson’s Disease.

Language

Thirdly, Parkinson’s Disease affects language. Language refers to the ability to name objects, generate words, comprehend, and verbal conception. According to Baiano et al. (2020), the most common language problem associated with Parkinson’s Disease is finding the ‘right’ words. Additionally, people suffering from this condition tend to speak less in general and tend to use simpler speech. This can lead to frustrations for the patient and their care partners due to the need for effective verbal communication (Aarsland et al., 2021). Therefore, language is essential in clinical diagnosis of Parkinson’s Disease.

Visuospatial function

Fourthly, Parkinson’s Disease commonly affects visuospatial function. Visuospatial function refers to the ability to inform a person where items are located in their surroundings, offering a special map of the surroundings, and incorporating one’s sense of direction. The visuospatial function allows individuals to copy drawings, depth perception, estimate distance, or construct shapes or objects. For instance, giving other people directions to a given destination by tracing the route in one’s mind, putting puzzles together, and avoiding obstacles in one’s path. Thus, visuospatial function impairment is normally employed in diagnosis of Parkinson’s Disease.

Cognitive Changes

Further, Parkinson’s Disease tends to cause cognitive changes. Not every patient experience cognitive change, and in some individuals, the effects are mild (Martinez-Horta & Kulisevsky, 2019). However, some individuals may suffer severe effects impacting their daily functionality. Apart from slowness of movement, individuals with the disorder tend to report slower information processing and thinking. The most commonly affected cognitive domains in individuals with Parkinson’s Disease include executive function, working memory, and visuospatial function.

Parkinson’s Disease usually causes mild cognitive impairment. Mild cognitive impairment does not impair individual from carrying out their daily activity. It is estimated that about 20% to 50% of patients with the disorder tend to have mild cognitive disorder. It has recently been established that these mild cognitive changes are often present at the time of disorder diagnosis or even during the early stages of the disease (Baiano et al., 2020). Mild cognitive impairment, may be unnoticeable to the individual, and may or may not affect their daily activities, based on the demand of these tasks.

Dementia

A syndrome that leads to issues in more than one cognitive domain is called dementia. The syndrome significantly impairs an individual’s daily activity. According to Goldman & Sieg (2020), about 40% of individuals with Parkinson’s Disease tend to develop dementia. Martinez-Horta & Kulisevsky (2019) explain that dementia in these individuals usually develops many years after the onset of the disorder and is typical with advanced stages of the disease.

Patients with dementia are commonly diagnosed with dementia with Lewy bodies. In cases where dementia develops before or during the onset of the disorder motor symptoms, patients usually get diagnosed with dementia with Lewy bodies. According to Martinez-Horta & Kulisevsky (2019), recent studies have also indicated that the mean time to development of dementia after Parkinson’s Disease diagnosis is about 10 years. Martinez-Horta & Kulisevsky (2019) explain that the prevalence of dementia is 15-20% five years after diagnosis and 46% ten years after diagnosis with Parkinson’s Disease. Martinez-Horta & Kulisevsky (2019) reported that of patients with Parkinson’s Disease who had normal cognition, about 50% of them developed cognitive decline after 6 years. Martinez-Horta & Kulisevsky (2019) also note that cortical posterior cognitive deficit that is language and memory impairment, but not frontally based dysfunction, are associated with a high risk of dementia, thus the ‘dual syndrome hypotheses’ of cognition in Parkinson’s Disease. Essentially, there have been different results in different studies relating to Parkinson’s Disease which is likely a result of different factors such as varied case selection, the stage of Parkinson’s Disease at the research took place, loss to follow-up, and the criteria for determining dementia and mild cognitive disorder in Parkinson’s Disease.

Clinical Diagnosis Challenges Associated with Parkison’s Disease

There are clinical challenges relating to cognitive decline in Parkinson’s Disease. According to Aarsland et al. (2021)., cognitive decline in Parkinson’s Disease is progressive and affects almost all patients over time, and the division between subjective cognitive decline, mild cognitive disorder, and Parkinson’s dementia disorder is not strict. Patients’ distribution among these categories varies in different studies, depending on the criteria applied, case selection procedures, cognitive measurement procedures utilized, and the study design. For instance, a recent study aiming to define the optimal criteria for Parkinson’s Disease mild cognitive disorder established that impairment was greater than 1.5 standard deviation which was below the normative mean (Martinez-Horta & Kulisevsky, 2019). This was from two tests done within the same cognitive domain rather than different domains, which provided the best prediction of dementia over a period of four years. Essentially, the separation of dementia and mild cognitive impairment is based on whether the functional effects of cognitive impairment are ‘severe enough to affect daily activity’ a system that is difficult to operationalize and needs elements of clinical judgment.

Also, the distinction between Parkinson’s dementia disorder and dementia with Lewy bodies is a major challenge. This is because of their pathological and clinical overlap. In the ‘1-year rule’, Parkinson’s dementia disorder is given as dementia that develops at least one year after the onset of Parkinson’s Disease motor symptoms (Aarsland et al., 2021). On the other hand, dementia that develops before, hand in hand with, or within the first year of developing parkinsonism is classified as dementia Lewy body, is usually difficult to apply since a significant population of the patients lie within the grey area, with categorization often being applied retrospectively. Also, prodromal Parkinson’s Disease and dementia Lewy body symptoms overlap. For instance, REM sleep behavior disorder can develop into either dementia Lewy body, or Parkinson’s Disease (Martinez-Horta & Kulisevsky, 2019). Evidence has also been shown indicating that cognitive impairment can present itself in prodromal Parkinson’s Disease, which continues to blur the difference between dementia Lewy body and Parkinson’s Disease. MSD diagnosis criteria have recently been revised for Parkinson’s Disorder and proposes that the disease can be diagnosed even when dementia occurs concerning parkinsonism onset, and in instances where parkinsonism subsequently develops in dementia patients, with the diagnosis being recommended. According to Sun & Armstrong (2021), the relationship between dementia Lewy body and Parkinson’s Disease requires further studies. For instance, some recent studies have shown that some nonmotor subtypes of Parkinson’s Disease, including non- and cognitive forms, may occur in early untreated motor conditions in progressed Parksion Disease, in addition to early-onset Parkinson’s Disease (Sun & Armstrong, 2021). From a practical point of view, an algorithm in which pre-motor non-motor symptoms and signs such as rapid eye movement sleep behavior disorder are directed towards potential evolution to motor Parkinson’s Disease, including cognitive phenotypes has been proposed. Thus, there are major challenges affecting diagnosis of Parkinson’s Disease, and with intense research this issues can be addressed.

Conclusion

Parkinson’s Disease not only leads to motor impairment but also cognitive impairment. The are mild cognitive impairment and severe cognitive impairment that usually hinders individuals from performing daily activities. Parkinson’s disease is also more common among elderly people compared to young people. The research has shown that almost half of people with Parkinson’s Disease develop dementia. There have been major challenges in the diagnosis of Parkinson’s Disease due to the gray line between dementia with Lewy body. Recent research has been focused on trying to address these challenges and allowing for effective clinical diagnosis. More research is necessary to improve clinical diagnosis of Parkinson’s disease with cognitive impairment.

References

Aarsland, D., Batzu, L., Halliday, G. M., Geurtsen, G. J., Ballard, C., Ray Chaudhuri, K., & Weintraub, D. (2021). Parkinson disease-associated cognitive impairment. Nature Reviews Disease Primers, 7(1), 47.

Baiano, C., Barone, P., Trojano, L., & Santangelo, G. (2020). Prevalence and clinical aspects of mild cognitive impairment in Parkinson’s disease: A meta‐analysis. Movement Disorders, 35(1), 45-54.

Goldman, J. G., & Sieg, E. (2020). Cognitive impairment and dementia in Parkinson disease. Clinics in geriatric medicine, 36(2), 365-377.

Martinez-Horta, S., & Kulisevsky, J. (2019). Mild cognitive impairment in Parkinson’s disease. Journal of Neural Transmission, 126(7), 897-904.

Sun, C., & Armstrong, M. J. (2021). Treatment of Parkinson’s disease with cognitive impairment: current approaches and future directions. Behavioral Sciences, 11(4), 54.