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Psychosis (delusions and/or hallucinations) is a common and problematic non-motor feature of Parkinson's disease (PD). Hallucinations are sensory perceptions that occur without external stimulation of the relevant sensory organ. In PD, a typical visual hallucination is a complex visual image experienced when the patient is alert and has their eyes open. The image usually appears somewhat blurred. There is a predominance of human or animal forms, some with emotional significance. The hallucinations are sometimes 'friendly'but may also consist of frightening images. Hallucinations are generally more common in the evening [1]. Most patients 'know'that they are hallucinating (benign hallucinosis), but approximately 5% experience delusions and hallucinations with lack of insight [2]. Auditory and tactile hallucinations may also occur, but are less frequent and usually co-exist with visual hallucinations [1]. A sense of presence is another common hallucinatory symptom.
Delusions are false beliefs based on incorrect inferences. They are commonly anteceded by hallucinations, but can occur in their absence. In PD, common themes of the delusions are spousal infidelity or persecution.
Estimates of prevalence vary. In one US study of 102 consecutive clinic attenders, a prevalence of visual hallucinations of 26% was found [3]. In a systematic review of clinic populations, the prevalence of hallucinations alone was between 21 and 46% [4]. A community survey in Norway yielded 9% prevalence for hallucinations and 6% for combined hallucinations and delusions [2]. In patients attending a specialist clinic, the figure for the combined symptoms was between 10 and 15% [5,6]. The combination of hallucinations and delusions together is regarded as a more serious problem as it usually results in subjective distress and behavioral disturbance.
Psychosis is an indicator of poor prognosis in PD [7] and is often the factor that leads to institutional care [8]. In addition, carer burden and mortality are high [7-10]. There is no consistent relationship with dose, drug type or on-off phenomena [11]. There is some evidence that the incidence of psychosis is higher in patients treated with dopamine agonists when compared with those receiving levodopa monotherapy [12-15].
Treating psychosis is one of the most difficult challenges for the parkinsonologist. Even in early monotherapy in new patients, drug- induced psychosis can be a major dose-limiting side effect. There is an increase in frequency with...