The psychiatric complications of Parkinson's disease.

Although James Parkinson in 1817 excluded mental symptoms from his original description of paralysis agitans, it has become clear that a wide range of psychiatric disorders can develop in patients with this disease. The principal conditions of dementia, depression and confusional syndromes, many of which are precipitated by drugs used in the treatment of parkinsonism, are reviewed. Particular attention is given to the frequency of dementia and its likely pathogenesis, to the nature of depression in Parkinson's disease and to the effects of different drugs, notably levodopa. A number of rare disorders characterised by parkinsonian and psychiatric symptoms are also discussed.