Differential Diagnosis

• Single most likely diagnosis
  • Delirium: The patient's acute onset of agitation, hallucinations, difficulty falling asleep, and difficulty following simple commands are classic symptoms of delirium. The fact that she has a history of dementia, which is a risk factor for delirium, and that there has been no recent change in her medications, makes delirium the most likely diagnosis.
• Other Likely diagnoses
  • Worsening dementia: Although the patient's symptoms have acutely worsened, it is possible that her dementia is progressing, leading to increased agitation, hallucinations, and difficulty with sleep and focus.
  • Anxiety: The patient's agitation and difficulty falling asleep could be symptoms of anxiety, although anxiety alone would not typically cause hallucinations or difficulty following simple commands.
• Do Not Miss
  • Infection (e.g. UTI, pneumonia): Infections can cause delirium, especially in elderly patients with dementia. It is crucial to rule out an underlying infection, as it would require prompt treatment.
  • Medication side effects: Although the patient's medications have not recently changed, it is still possible that she is experiencing side effects from her current medications, such as memantine.
  • Electrolyte imbalance: Electrolyte imbalances, such as hyponatremia or hypernatremia, can cause delirium and would require prompt treatment.
• Rare diagnoses
  • Parkinson disease: Although the patient is taking memantine, which is sometimes used to treat Parkinson's disease, there is no other indication in the history that she has Parkinson's disease, making this diagnosis less likely.
  • Depression: While depression can cause changes in sleep and mood, it would not typically cause acute hallucinations or difficulty following simple commands, making it a less likely diagnosis in this case.