In an 83‑year‑old woman with Alzheimer’s disease, mild mixed dementia, major depressive disorder, insomnia, aphasia, and vitamin D deficiency who is now exhibiting evening‑time paranoid accusations (sundowning) and has a negative urine culture, what is the likely cause of her psychosis and what medication is recommended for treatment?

Likely Cause and Treatment for Evening Psychosis in This Patient

The psychosis is most likely sundowning—a manifestation of her underlying Alzheimer's disease characterized by worsening neuropsychiatric symptoms in late afternoon/evening—and if pharmacologic treatment becomes necessary after non-pharmacologic interventions fail, use a low-dose atypical antipsychotic such as quetiapine, which has the lowest adverse event profile in older adults.

Understanding the Cause: Sundowning

The evening-time paranoid accusations about stolen shoes represent sundowning, a well-documented phenomenon in Alzheimer's disease where neuropsychiatric symptoms emerge or worsen in late afternoon/early evening 1, 2, 3. This patient's presentation is classic:

• Prevalence: Sundowning occurs in 21-51% of Alzheimer's patients 1, 2
• Common manifestations: Agitation (56%), irritability (54%), anxiety (46%), and suspiciousness—exactly what your patient exhibits 2
• Associated factors: More severe cognitive impairment (Clinical Dementia Rating score), older age, and nocturnal awakenings 2

Pathophysiology

The mechanism involves cholinergic neuronal degeneration in the Nucleus basalis Meynert, which disrupts the suprachiasmatic nucleus (the brain's circadian pacemaker) and impairs the transition to NONREM sleep 4. Essentially, arousal processing occurs while the neocortex is already "turned off" for sleep, creating behavioral disturbances 4.

Important Note on Current Medications

Your patient is NOT on memantine at therapeutic doses—she's only on 5 mg BID (10 mg/day total), which is the starting dose. Research shows memantine use is protective against sundowning (OR 0.20) 2, suggesting her current subtherapeutic dosing may be contributing to the problem.

Treatment Algorithm

Step 1: Optimize Non-Pharmacologic and Existing Medications FIRST

Before adding antipsychotics:

1. Titrate memantine to therapeutic dose (20 mg/day): Increase by 5 mg weekly to reach 10 mg BID. This has protective effects against sundowning 2 and may address the psychosis without additional medications.

2. Strengthen external zeitgebers (circadian cues) 4:

   • Maximize bright light exposure during daytime hours
   • Maintain strict sleep-wake schedule
   • Minimize evening stimulation and noise
   • Ensure adequate vitamin D supplementation is continued (already prescribed)

3. Review for anticholinergic burden: Avoid medications with anticholinergic properties, as these are associated with increased sundowning 2

Step 2: If Pharmacologic Treatment Becomes Necessary

Only proceed if the psychosis is dangerous, causes significant distress, or non-pharmacologic measures fail 5.

Recommended Medication: Quetiapine

• Dosing: Start 12.5-25 mg in the evening, titrate slowly
• Rationale: Quetiapine showed the lowest adverse event profile in older adults with agitation (OR 0.27 compared to haloperidol) 6
• Timing: Administer in late afternoon before sundowning typically begins

Critical Safety Considerations

The APA guidelines emphasize that antipsychotic benefits in dementia are "at best small" while adverse effects including mortality are clinically significant 5. You must:

• Obtain informed consent from the patient's surrogate decision maker
• Document that benefits (reducing distress, preventing harm) outweigh risks
• Use the lowest effective dose for the shortest duration
• Monitor for adverse effects: falls, sedation, extrapyramidal symptoms, metabolic changes

Step 3: Medications to AVOID

Never use benzodiazepines (especially midazolam) in this population—they carry a 5.25-fold increased risk of adverse events compared to antipsychotics 6 and can worsen delirium and cognitive function.

Common Pitfalls to Avoid

1. Jumping to antipsychotics without optimizing memantine: Her current dose is subtherapeutic
2. Treating sundowning as a psychiatric emergency: Unless she's dangerous, this is a chronic management issue requiring environmental and medication optimization first
3. Using first-generation antipsychotics: Haloperidol has higher adverse event rates than atypical agents 6
4. Ignoring the circadian component: Pharmacology alone without addressing sleep-wake cycles and light exposure will be less effective 4

Monitoring Plan

If antipsychotic is initiated:

• Reassess weekly for efficacy and adverse effects
• Attempt dose reduction or discontinuation after 3-4 months if symptoms stabilize
• Monitor for falls, sedation, gait changes, and metabolic parameters

The goal is symptom control with minimal medication burden, prioritizing quality of life and safety over complete symptom elimination 5.