Diagnosis of dementia in Parkinson's disease

Murat Emre


In essence, diagnosis of dementia in a patient with Parkinson’s disease (PD) is no different from diagnosing dementia in any other patient. The diagnostic approach can be conceptualized as a two-step process: diagnosis of dementia and differential diagnosis with regard to its aetiology. The first step involves excluding other conditions which can mimic dementia, as well as evaluating whether mental impairment is severe enough to affect normal functioning by itself in order to fulfil the current definition of dementia. The second step includes the assessment of the aetiology,

i.e. whether dementia is due to PD, by excluding other potential causes. Although rather straightforward in a patient with a typical history and symptoms of PD, this step involves considering other conditions which can present with dementia and parkinsonism, particularly in patients for whom the history is not reliable or when atypical features are present.

Compared with other patients with suspected dementia, diagnosis of dementia in patients with PD can be more difficult. There are several confounding factors related to the disease itself, its treatment, and co-morbid conditions which are more frequent in this patient population. These include adverse effects of medication, acute or prolonged confusion due to systemic abnormalities or diseases, and the presence of depression, all of which can mimic symptoms of dementia. At times, severe motor impairment renders it difficult to judge whether impairment in function, a prerequisite for the diagnosis of dementia, is due to mental or motor dysfunction. Conditions that can mimic dementia in patients with PD are listed in Table 20.1 and the general approach to diagnosis is summarized in the rest of this chapter.

Diagnosis of dementia

Diagnosing dementia in patients with PD (PD-D) is principally a clinical undertaking, with little help from auxiliary methods. The diagnostic process involves several components, including a careful history from patients and their family members with emphasis on typical features of PD-D [1], assessment of cognitive functions, behavioural symptoms, and activities of daily living (ADL). In typical cases auxiliary examinations are of least help—they usually serve the purpose of excluding alternative aetiologies in suspected patients.

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