What is the most likely diagnosis and optimal management for an elderly hospitalized patient with impaired attention, acute psychosis, and fluctuating levels of consciousness, who was admitted for pneumonia treatment?

Delirium with Immediate Investigation Required

This patient's impaired attention, acute psychosis with fluctuating consciousness (calm during day, agitated at night), and disorientation in the setting of pneumonia are most consistent with delirium, which requires immediate investigation and management. 1, 2, 3

Why This is Delirium, Not Schizophrenia or Dementia

Core Diagnostic Features Present

• Acute onset over hours to days (admitted 2 days ago for pneumonia) with fluctuating course (calm and alert in morning, agitated with hallucinations at night) are pathognomonic for delirium 1, 2, 4
• Impaired attention is the cardinal feature—patient cannot recall why hospitalized despite being alert, indicating profound inattention rather than memory loss 1, 3
• Altered level of consciousness that waxes and wanes distinguishes delirium from primary psychiatric disorders like schizophrenia, which maintain intact awareness 1, 2
• Visual hallucinations (animals in bed) combined with disorientation are classic delirium features, not typical of late-onset schizophrenia 1, 2

Why Not Schizophrenia

• Schizophrenia does not present with fluctuating consciousness or acute onset in elderly patients 1, 2
• Schizophrenia maintains clear sensorium and does not follow a waxing/waning pattern 1
• New-onset psychosis in an elderly hospitalized patient with medical illness is delirium until proven otherwise 2

Why Not Major Neurocognitive Disorder (Dementia)

• Dementia is a chronic condition with gradual onset, not acute changes over 2 days 1
• Dementia patients have clear sensorium without cyclic symptom patterns 1
• The acute presentation with infection (pneumonia) as precipitant points to delirium, though delirium can occur superimposed on underlying dementia 1, 2

Why Immediate Investigation is Critical

Delirium is a Medical Emergency

• Delirium doubles mortality when the underlying cause is not promptly identified and treated 2
• Pneumonia is a common precipitating factor for delirium in elderly patients, representing a life-threatening infectious process requiring urgent management 1, 2, 3
• The American College of Radiology emphasizes that identifying acute intracranial pathology or systemic causes in altered mental status patients is "extremely important to guide management and ensure early appropriate triage" 1

Required Immediate Workup

• Laboratory investigations guided by clinical evaluation: complete blood count, comprehensive metabolic panel, urinalysis, blood glucose, thyroid function 3
• Chest radiography to fully evaluate pneumonia severity and complications 1, 3
• Electrocardiogram to assess for myocardial ischemia or arrhythmias 3
• Medication review for deliriogenic agents (anticholinergics, benzodiazepines, sedatives) 2, 3
• Neuroimaging (CT head without contrast) if focal neurological deficits develop, history of head trauma, or unexplained altered mental status despite initial workup 1, 3

Why Deferring to Outpatient Setting is Dangerous

• Delirium in hospitalized elderly patients has prevalence of 7-35% and represents acute brain dysfunction requiring immediate intervention 1, 3
• Untreated delirium leads to prolonged hospital stays, increased complications, and significantly increased mortality 2, 3
• The underlying cause (pneumonia in this case) requires active inpatient treatment, not outpatient follow-up 1, 2

Critical Clinical Pitfall to Avoid

The most common error in geriatric emergency care is attributing all symptoms to dementia progression or psychiatric illness without investigating acute medical causes 2, 5. This patient's presentation screams delirium: acute onset, fluctuating course, inattention, altered consciousness, and a clear precipitant (pneumonia). Missing this distinction and referring to psychiatry or deferring evaluation would be potentially fatal 2.