Descriptions of drug-induced parkinsonism (DIP) began to appear early in the decade that followed the introduction of antipsychotic medications (Lehmann & Hanrahan, 1954; Hall, Jackson, & Swain, 1956; Deniker, 1960; Kruse, 1960; Goldman, 1961; McGeer et al., 1961; Ayd, 1961; Simpson et al., 1964). DIP is one of the most common side effects of antipsychotic medications. Although other syndromes may have received more attention, because of their apparent irreversibility or because of novelty of presentation, DIP probably causes the greatest morbidity. This chapter will review the typical clinical presentation, differential diagnosis, epidemiology, evaluation, pathophysiology, and treatment for this major iatrogenic problem.

Clinical Presentation

Description of the Syndrome

All the cardinal signs of idiopathic Parkinson's disease (IPD) occur in DIP (Hall et al., 1956; Lader, 1970; Goetz & Klawans, 1981; Rajput, 1984; Casey, 1991; Friedman, 1992). Although some authors have used the term “pseudoparkinsonism” to describe DIP, given that DIP and IPD appear to have the same symptoms and basic biochemical mechanism, that term is no longer favored. The signs of DIP can be grouped into five categories: bradykinesia, rigidity, tremor, loss of postural reflexes, and a miscellaneous category. This grouping of specific motor signs is somewhat arbitrary, for the causes of the signs cannot always be determined, and the groups are not entirely independent.