Differential Diagnosis for a 92-year-old Female with Agitation, Delusions, and Confusion

Single Most Likely Diagnosis

• Withdrawal from Donepezil: Stopping donepezil abruptly after a period of use can lead to withdrawal symptoms, which may include agitation, delusions, and increased confusion. Given the timeline of stopping the medication 84 days ago and the onset of symptoms approximately two weeks ago, it's plausible that the patient is experiencing a delayed withdrawal effect, although the typical timeframe for withdrawal symptoms to appear is usually sooner.

Other Likely Diagnoses

• Progression of Underlying Dementia: The patient's symptoms could be due to the natural progression of her underlying dementia, which may have been partially managed by the donepezil. Stopping the medication could unmask the progression of the disease.
• Infection: Despite the negative UA, other infections (e.g., pneumonia, urinary tract infection not detected by UA) could be causing her symptoms. Infections can present atypically in the elderly, with confusion, agitation, and delusions being common manifestations.
• Medication Side Effects or Interactions: Introduction of new medications or changes in existing medications (other than donepezil) could be contributing to her symptoms. Polypharmacy is common in the elderly and increases the risk of adverse drug reactions.

Do Not Miss Diagnoses

• Vitamin B12 Deficiency: A deficiency in vitamin B12 can cause neurological symptoms including confusion, agitation, and delusions. It's essential to rule out this condition due to its potential for irreversible neurological damage if left untreated.
• Thyroid Dysfunction: Both hyperthyroidism and hypothyroidism can cause cognitive symptoms and mood changes. Given the potential severity of untreated thyroid disorders, it's crucial to consider and rule out these conditions.
• Subdural Hematoma or Other Intracranial Pathology: Trauma, even minor, can lead to subdural hematomas in the elderly, presenting with confusion, agitation, and delusions. This is a medical emergency requiring immediate attention.

Rare Diagnoses

• Creutzfeldt-Jakob Disease: A rare, degenerative, fatal brain disorder that can cause dementia, confusion, agitation, and delusions. It's essential to consider this, although it's rare, due to its distinct implications for patient care and prognosis.
• Neurosyphilis: If the patient has a history of syphilis, neurosyphilis could be a consideration, presenting with psychiatric symptoms, cognitive decline, and personality changes.