Lithium toxicity and prolonged delirium

To the Editor

Lithium neurotoxicity usually occurs in the context of chronic therapeutic administration of lithium rather than an acute overdose of lithium, which highlights the need for vigilant monitoring in susceptible individuals (Oakley et al., 2001). We describe a case of lithium toxicity and subsequent prolonged delirium to underscore the necessity for close monitoring and clinical assessment of individuals who are prescribed lithium.

MR, a 63-year-old retiree with brittle bipolar disorder living in rural Australia, was hospitalized for over 3 months for treatment of depression. Historically, her bipolar illness was characterized by multiple affective switches followed by a lack of stability or return to euthymia. Upon admission, MR was found to be lithium toxic, and was immediately transferred to a general medical ward for treatment and stabilization. She was transferred back to our psychiatric unit on low-dose lithium. Her depressive episode was complicated by a protracted delirium, characterized by cognitive impairment, social withdrawal and reversal of her sleep-wake cycle. She resisted nonpharmacological interventions to manage her delirium and remained basically bed-bound, which contributed to other medical complications. Most of her psychotropic medications were reduced or ceased during this period, including lithium as she could no longer tolerate an increased dose without worsening confusion.

MR’s lengthy delirium, which took 5 weeks to resolve, was likely a marker of her underlying brain vulnerability and decreased resilience to external triggers. The development of delirium is often multifactorial, especially in older individuals, with a complex interplay between predisposing and precipitating factors. Thus, prevention and treatment approaches must be multifaceted in nature. Prolonged delirium itself might lead to permanent cognitive decline, which is itself a predisposing factor for future episodes of delirium (Inouye et al., 2014).

MR had right unilateral ultra-brief electroconvulsive therapy (ECT) to treat her severe depression, and her mood and psychomotor functioning gradually improved. However, she developed hypomania after her seventh treatment. ECT was suspended, and she was commenced on carbamazepine and quetiapine. Within approximately 1 week, her mood stabilized, and she was discharged in a euthymic state.

Lithium remains a highly effective treatment with Level 1 evidence for both unipolar and bipolar disorders, but its clinical use has to be tempered against potential side-effects and the need for ongoing monitoring (Malhi et al., 2016). Individuals like MR who are living in remote areas may have limited access to psychiatric care, making proper monitoring even that much more difficult.