Parkinson's disease and hallucinations

   The eponym Parkinson's disease refers to the British physician James Parkinson (1755-1824), who has been credited with being the first to describe the concomitant disease in 1817. The eponym itself was coined during the 1870s by the French neurologist Jean Martin Charcot (18251893). Parkinson's disease is primarily classified as a movement disorder, or, more specifically, as a disorder of the extrapyramidal system. It is characterized by a variety of motor signs, including tremor (usually at rest), a stooped posture, impaired postural reflexes, rigidity, a mask-like facies, a reduced blink rate, apraxia, akathisia, dyskinesia, and bradykinesia or even akinesia. It may be accompanied by a variety of non-motor complications such as depression, paranoia, delusions, * delirium, hallucinations, impaired colour vision and contrast discrimination, cognitive disturbances, sleep-wake cycle disturbances, and speech disorders. These symptoms may also occur in the context of parkinsonism, a syndrome with similar features that is not necessarily due to idio-pathic Parkinson's disease. As to its pathophys-iology, Parkinson's disease is attributed primarily to impaired functioning of the motor cortex, which is in turn attributed to the insufficient production and action of dopamine within the basal ganglia. In outpatient populations of individuals suffering from Parkinson's disease, hallucinations have been reported in up to 25% of cases. The lifetime prevalence of hallucinations has been estimated at around 46%. Most of these hallucinations are visual in nature. They typically consist of * complex hallucinations depicting persons, humanoidfigures, animals (i.e. *zoopsia), or objects. Hallucinations occurring in the context of Parkinson's disease can also be * compound in nature, combining visual and auditory elements in the majority of these cases. Isolated auditory hallucinations and * simple hallucinations are rarely reported. Tactile hallucinations are even less prevalent. If present, they tend to be long lasting and to coincide with the visual hallucinations. In addition, Parkinson's disease may be complicated by * illusions and so-called * minor hallucinations such as * sensed presence and * passage hallucinations. It has been suggested that the relatively low prevalence of simple hallucinations in Parkinson's disease is due to underreporting. Etiologically, hallucinations and illusions in Parkinson's disease are sometimes attributed to the disease itself. However, the majority of these perceptual symptoms are attributed to the dopatherapy that is often prescribed, even though a dose-related effect has never been established. The mediation of hallucinations and illusions in Parkinson's disease can probably be best explained by reference to a multi-factorial model that takes into account the various pharmacological agents involved, disturbances of the circadian rhythm, and cognitive impairment, as well as the influence of comorbid disorders such as dementia and ocular disease.

   References

   Fénelon, G., Mahieux, F., Huon, R., Ziégler, M. (2000). Hallucinations in Parkinson's disease: Prevalence, phenomenology and risk factors. Brain, 123, 733-745. Parkinson, J. (1817). An essay on the shaking palsy. London: Sherwood, Neely and Jones.