The definition of psychotic symptoms (i.e., delusions, delusional misidentification, and hallucinations) requires particular consideration as these symptoms are very frequent in some parkinsonian disorders, particularly in patients with dementia. In addition, as they are phenomenologically different from psychotic symptoms occurring in patients with functional psychoses and cannot be reliably observed or inferred from behavior, a specific method is required to identify these symptoms in patients with cognitive impairments. According to Burns, delusions are defined as false, unshakable ideas or beliefs that are held with extraordinary conviction and subjective certainty (3). To minimize overlap with confabulation and delirium, they should be reiterated on at least two occasions more than 1 wk apart. Hallucinations are described as percepts in the absence of a stimulus, reported directly by either the patient or indirectly via an informant, and may occur in any modality. Typically, visual hallucinations are the most common type of hallucinations encountered in patients with parkinsonian disorders. Delusional misidentification, including the Capgras syndrome (the belief that a person, object, or environment has been replaced by a double or replica), delusional misidentification of visual images (whereby figures on television or in photographs are thought to exist in the real environment), delusional misidentification of mirror images (one's reflection is perceived as the image of a separate person), and the phantom boarder delusion (believing that strangers are living in or visiting the house) are also commonly encountered in parkinsonian patients.
The diagnosis of depression in parkinsonian disorders may be difficult, and both over- and underdiagnosis may occur. The motor symptoms may mask the affective features, leading to underdiagnosis, whereas the psychomotor slowing, apathy and masked facies may be erroneously interpreted as depression. Although most reports indicate that the symptoms of depression are broadly similar in people with or without a parkinsonian disorder, patients with PD may have more commonly dysphoria and pessisimism, but less commonly guilt, self-blame, and suicidal behavior than subjects without a parkinsonian disorder. Symptoms such as fatigue, apathy, sleep, and appetite disturbance may occur independently of mood as an intrinsic part of the neurodegenerative process. The nonsomatic symptoms of depression appear to be the most important for distinguishing between depressed and nondepressed patients with parkinsonism (4). Dementia may further complicate the diagnosis of depression in these patients because patients are unable to verbalize their subjective experience. Despite this, there is evidence that depression can be reliably and validly diagnosed even in patients with a parkinsonian disorder using standardized depression-rating scales (see below).
Apathy consists of lack of motivation with diminished goal-directed behavior, reduced goal-directed cognition, and decreased emotional engagement. Apathy may accompany depression, but it is often an independent syndrome without the sadness, despair, and intense suffering typically experienced by depressed patients (5). Apathy is commonly accompanied by evidence of executive dysfunction.
Anxiety is characterized by excessive and unjustified apprehension, feelings of foreboding, and thoughts of impending doom. Patients are tense and irritable, and frequently exhibit autonomic disturbances including sweating, palpitations, gastrointestinal distress, and shortness of breath. Both low-grade, free-floating anxiety and acute and intense panic attacks may occur.
Although less frequently reported, a number of other neuropsychiatric symptoms need to be mentioned. Agitation, such as aggression, restlessness, and shouting, can usually be observed, and thus the identification of these symptoms is less problematic. However, key symptoms of agitation are often secondary to other psychiatric syndromes. For example, anxiety may lead to restlessness, shouting, or trailing carers, or aggression may be secondary to delusional beliefs. Disinhibition is characterized by inappropriate social and interpersonal interactions. Elation/euphoria refers to an elevated mood with excessive happiness and overconfidence, and obsessional and compulsory symptoms, with recurrent thoughts, vocalizations, or rituals, may also occur in basal ganglia disorders.
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