Is lithium used for treatment of unipolar depression in a 71-year-old patient with potential cognitive decline and impaired renal function, or is it primarily used for bipolar disorder?

Lithium Use in Your 71-Year-Old Patient

Lithium is FDA-approved specifically for bipolar disorder (manic episodes and maintenance treatment), not for unipolar depression alone, so your patient either has undiagnosed bipolar disorder or is receiving lithium as augmentation therapy for treatment-resistant depression. 1

Primary Indication Assessment

Your patient most likely falls into one of two scenarios:

• Bipolar disorder with poor recall of manic episodes: Elderly patients with cognitive decline may not accurately report past manic or hypomanic episodes, particularly if they occurred years ago. 2 The presence of lithium strongly suggests a bipolar diagnosis was made at some point, as lithium is the gold standard for bipolar maintenance treatment. 3

• Treatment-resistant unipolar depression with lithium augmentation: While lithium is primarily indicated for bipolar disorder 1, it has demonstrated efficacy as an adjunctive antidepressant in treatment-resistant unipolar depression, though this is an off-label use. 3

Critical Actions for This Patient

Obtain Collateral History

• Contact previous prescribers or review old records to determine the original indication for lithium, as your patient's cognitive impairment makes her an unreliable historian. 2
• Interview family members about any history of manic symptoms (decreased need for sleep, increased energy, impulsivity, excessive spending, hypersexuality, grandiosity). 1
• Review medication history for patterns suggesting bipolar disorder (multiple antidepressant trials, antipsychotic use, mood stabilizers). 4

Assess Renal Function Immediately

• Calculate creatinine clearance using Cockcroft-Gault equation, not just serum creatinine alone, as elderly patients have reduced muscle mass that masks true renal impairment. 2
• Monitor for progressive renal dysfunction: Approximately 20% of patients on long-term lithium develop some decrease in renal function, and a small minority may progress to renal failure. 5, 6
• Consider discontinuation if creatinine clearance approaches 40 mL/min or serum creatinine consistently exceeds 200 μmol/L (approximately 2.3 mg/dL), as limited data suggest this threshold for stopping lithium. 6

Monitor for Cognitive and Safety Risks

• Elderly patients with cognitive impairment have increased susceptibility to lithium accumulation and a narrower therapeutic window, making confusion and toxicity more likely. 2
• Implement fall risk assessment, as lithium can cause tremor, cognitive dulling, and orthostatic hypotension in elderly patients. 2, 3
• Check lithium levels more frequently (every 3-6 months minimum) and maintain at the lowest effective concentration, as age-related decline in renal function (approximately 1% per year after age 40) increases toxicity risk. 2, 4

Comprehensive Monitoring Protocol

Baseline and ongoing monitoring should include: 4

• Renal function and electrolytes every 3-6 months
• Thyroid function every 3-6 months (lithium increases hypothyroidism risk)
• Complete blood count and comprehensive metabolic panel
• Lithium levels to maintain therapeutic range (0.5-1.2 mM for bipolar disorder)

Clinical Decision Algorithm

If bipolar disorder is confirmed:

• Continue lithium with close monitoring, as it remains the gold standard for bipolar maintenance treatment with unique anti-suicide properties (reducing suicide attempts 8.6-fold). 4, 3

If only unipolar depression is documented:

• Verify lithium is being used as augmentation for treatment-resistant depression
• Consider whether alternative strategies (switching antidepressants, adding psychotherapy) might be safer given her age and cognitive status
• If continuing lithium, ensure she has failed adequate trials of other antidepressants to justify the risks

If renal function is significantly impaired (CrCl <40 mL/min):

• Strongly consider discontinuing lithium and transitioning to alternatives like valproate or atypical antipsychotics, though these also carry risks in elderly patients. 4, 6

Common Pitfalls to Avoid

• Do not rely solely on serum creatinine in elderly patients—always calculate creatinine clearance. 2
• Do not assume the patient can accurately report psychiatric history when cognitive impairment is present—obtain collateral information. 2
• Do not continue lithium without verifying the indication, as the risk-benefit ratio differs substantially between bipolar disorder (where lithium is uniquely effective) and unipolar depression (where safer alternatives exist). 1, 3
• Do not overlook polypharmacy risks, as elderly patients commonly take multiple medications that increase drug-drug interaction risks. 2