A 61-year-old with bipolar disorder and cognitive impairment: Dementia or polypharmacy?

FOLLOW-UP COURSE

We informed the patient’s psychiatrist that we thought the patient had increased sensitivity to lithium (even at “therapeutic” levels), possibly related to a drug-drug interaction.

His dose of lithium was kept at 600 mg twice daily, as the lithium toxicity was most likely due to a drug-drug interaction.

We discontinued his memantine, since he did not have Alzheimer disease and since he wasn’t taking it anyway. He continued taking gabapentin and divalproex at the same doses, and he stopped taking naproxyn and substituted acetaminophen for his arthritis pain. We advised him about about health maintenance, including proper nutrition, mineral and vitamin supplements, and exercise.

The patient underwent neuropsychological testing to better characterize his cognitive impairment. The findings did not suggest dementia, but were consistent with minor cognitive deficits caused by lithium.

When seen at a follow-up visit 6 weeks later the patient was free of symptoms except for the tremor in his dominant hand. His mood was stable and his cognition was better. No further changes were required in his psychotropic drug regimen.

TAKE-HOME POINTS

When a bipolar patient develops acute changes in cognition, we should suspect adverse effects of lithium as the cause, because of its narrow therapeutic window and interactions with other prescribed drugs. The case presented here reminds us to consider adverse drug effects any time an older patient develops acute changes in cognition. One should also consider the potential for a drug-drug interaction when reviewing the patient’s medication list and be especially vigilant in monitoring patients taking lithium, since its safety and effectiveness are affected by aging and by the co-administration of drugs that influence its clearance.

Despite these caveats, lithium remains an effective treatment in elderly patients, provided we are aware of the risks and benefits of its use.