Reversible Lithium Toxicity Misdiagnosed as Dementia in an Elderly Patient: A Case Report and Follow-Up to Previous Work on Lithium Sensitivity in Aging

Lithium is a widely used mood stabilizer but requires careful management in the elderly due to altered pharmacokinetics and pharmacodynamics. This case report describes a dramatic reversal of apparent end-stage dementia in an 85-year-old woman after recognition and correction of chronic lithium toxicity. The case is of interest because over a two-year period of the case, the average lithium level, creatinine level, and eGFR remained the same, yet the lithium became toxic. It demonstrates that even though the eGFR remains constant, the dose of lithium may need to be reduced with aging to keep the lithium level therapeutic. It reinforces and expands upon previous findings that therapeutic serum lithium levels can become toxic with aging due to physiological changes, particularly in renal function and neural sensitivity. The woman is in stage four of chronic kidney disease, which means there is a very small therapeutic region for the lithium. The paper also describes how a second, unusual form of dementia, caused by lithium toxicity, was diagnosed and treated.