Disabling parkinsonism due to lithium: a case report.

Two cases of disabling parkinsonism have been previously reported in association with lithium treatment and only one occurred without other signs of lithium toxicity. We report a case of an elderly female who suddenly developed disabling parkinsonism, apparently as a side effect from treatment with lithium carbonate without other signs of lithium toxicity. All neurologic symptoms completely resolved on discontinuation of lithium. Resuming lithium at serum levels below 0.7 mmol/L resulted in no further neurologic side effects, but serum levels of 0.7 to 0.9 mmol/L resulted in the return of mild Parkinson's symptoms. Older age, longer duration of lithium treatment, and high therapeutic levels of lithium may be risk factors for this side effect. Implications for clinicians are discussed.