Cogwheel rigidity during chronic lithium therapy

The purpose of this study is to evaluate the presence of extrapyramidal symptoms, especially cogwheel rigidity, in patients receiving lithium alone or in combination with other medications (i.e., antipsychotic or dopamine-depleting agents). Cogwheel rigidity is commonly found in Parkinson’s disease and in drug-induced parkinsonism secondary to antipsychotic or dopamine-depleting agents (1). Its prevalence among lithium-tneated patients varies, but the occurrence of these symptoms suggests that lithium may cause extrapyramidal symptoms. Previous studies of cogwheel rigidity associated with lithium treatment (2-4) have lacked controls in three areas: 1) concomitant use of antipsychotic or dopamine-depleting drugs (which may induce extrapyramidal symptoms), 2) blindness of the evaluator to the patients’ drug status, and 3) laterality of cogwheel rigidity.