The measurement of psychiatric disturbances in patients with neurological disorders presents unique challenges. Because of the commonly co-occurring cognitive deficits, patients may not remember or report their symptoms. Furthermore, since these symptoms may fluctuate, the patients may not exhibit the symptoms at the time of the examination. It may thus be useful to infer symptoms from behavior or ascertain symptoms from an informant interview referring to a specific time period, in addition to the direct observation and interview of the patient.
A number of different instruments have been used to measure neuropsychiatry symptoms in patients with parkinsonian disorders. These can be divided into clinical interviews that focus upon a broad range of symptoms or more focused scales. Examples of the first group include the Present Behavioural Examination (PBE) (6), Neuropsychiatric Inventory (NPI) (7), and Brief Psychiatric Rating Scale (BPRS) (8). The PBE is a lengthy interview with a detailed assessment of behavior in patients with dementia, and requires a trained observer. The NPI is a highly structured, caregiver-based interview, which can be completed in a relatively short time depending on the amount of disturbances (see below). The BPRS was constructed essentially for schizophrenic states, and requires a trained rater. Examples of scales that assess specific syndromes in more detail are the Hamilton Depression Rating Scale (HAM-D) (9); and self-rating scales completed by the patients themselves (i.e., Beck Depression Inventory [BDI]) (10) and Geriatric Depression Scale (11). Acceptable psychometric properties of the PBE, BPRS, and NPI have been demonstrated in patients without parkinsonian disorders only, although interrater reliability of the NPI has been reported to be high in PD patients (12). The depression scales HAM-D, Montgomery & Asberg Depression Rating Scale (MADRS) (13), BDI (14), and Hospital Anxiety and Depression Scale (HAD) (15) have been validated in patients with PD. However, the cutoff scores may differ from nonparkinsonian subjects, and whereas lower cutoff scores are useful for screening purposes, higher scores are needed to make these scales good diagnostic instruments in these populations (13,14). Although qualitative differences of depression prevalence and phenomenology may exist between different parkinsonian disorders (16), it is reasonable to assume that the psychometric properties achieved in PD patients may apply for patients with atypical parkinsonian disorders as well.
The most widely used scale for the measurement of a broad range of psychiatric and behavioral symptoms among recently published studies in patients with neurological disorders is the NPI (see video). This is a highly structured, caregiver-based interview that rates frequency and severity of 10 psychiatric disturbances commonly observed in patients with different dementing conditions: delusions, hallucinations, agitation/aggression, dysphoria, anxiety, euphoria, disinhibition, apathy, irritability, and aberrant motor activity. The use of screening questions makes it easy to use in clinical practice, and the highly structured design suggests that the tool can be reliably used by individuals with low levels of training when provided with appropriate instruction regarding how to use the instrument. Since the NPI is scored on the basis of information provided by a caregiver, it avoids the problem inherent in observer-based strategies. On the other hand, it is subject to bias if the caregiver lacks or distorts information, and a caregiver with daily contact with the patient may not always be available.
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