Drug-induced parkinsonism.

Drug-induced parkinsonism (DIP) is condition that mimics Parkinson's disease. Characterized mainly by rigidity and bradykinesia, it has less prominent tremor and gait instability. DIP is generally caused by lipophilic drugs that "block" dopamine D2 receptors in the brain, although presynaptic dopamine depletion, false transmitters, mitochondrial respiratory chain dysfunction, and overactivity in the gamma-aminobutyric acid (GABA)ergic system or cholinomimetic action have also been postulated as possible mechanisms. The onset of DIP is acute to subacute. It is more common in women and has a bimodal age distribution. Other diseases that can resemble DIP include neuropsychiatric conditions (eg, depression, negative symptoms of schizophrenia) and Wilson's disease. Physicians may be able to prevent DIP by prescribing neuroleptic agents appropriately and with caution. The risk of DIP is presumably lower with the use of "atypical" antipsychotic agents but it is not eliminated, especially in those most vulnerable to parkinsonism (eg, the elderly or cognitively impaired). The best treatment is discontinuation of the provoking medication. Prospective studies are needed to further define the mechanism of DIP, identify individual susceptibility, determine the impact of atypical antipsychotic agents, and develop further treatment options for those unable to stop the offending agent.