Abstract

Lithium is commonly used to treat affective disorders. However, it has a narrow therapeutic index and incurs a considerable risk of toxicity, which can occur even within the therapeutic range. For older adults, this toxicity risk is particularly high because of age-related pharmacodynamic and pharmacokinetic changes and other comorbidities. A 69-year-old widow with bipolar disorder, Parkinsonism, and dementia was managing her conditions with lithium and Madopar. In the month before attending our hospital, she had been experiencing progressive cognitive decline, gastrointestinal discomfort, and general weakness, leading to a functional decline. Additionally, she had experiencing hand tremors, rigidity, and unsteady gait for 1 year. Her lithium serum levelwas 0.9 mmol/L. A Tc-99m TRODAT-1 brain single-photon emission computed tomography scan revealed normal perfusion in the bilateral basal ganglion, indicating secondary Parkinsonism rather than idiopathic Parkinson's disease. Therefore, lithium-related Parkinsonism was suspected. We tapered the dose of lithium and her condition gradually improved. We thus present a case of lithium toxicity related Parkinsonism and cognitive impairment and highlight the relevance of monitoring the required dose for older adults and understanding the various toxic effects of lithium, which can manifest even when a therapeutic level of lithium is used.