An older adult female with hypertension and type 2 diabetes presents with a 2‑day onset of fluctuating confusion, disorientation (worse at night), easy distractibility, and impaired recognition of family; which is the most likely diagnosis: Parkinson disease dementia, vascular dementia, delirium, or Alzheimer disease?

Acute Onset Fluctuating Course of Cognitive Impairment Consistent with Delirium

This patient's presentation is diagnostic of delirium, characterized by the acute 2-day onset, fluctuating course with periods of lucidity, worsening confusion at night, inattention (easy distractibility), and impaired recognition of family members. 1, 2

Clinical Reasoning

The temporal profile is the critical distinguishing feature here:

• Delirium develops over hours to days with symptoms that fluctuate within minutes to hours throughout the day, exactly matching this patient's 2-day timeline and fluctuating confusion with lucid intervals 1, 2

• Dementia (including Alzheimer's and vascular dementia) develops gradually over months to years with stable presentation throughout the day, making these diagnoses incompatible with the acute 2-day onset 2, 3

• Parkinson's disease dementia similarly follows a chronic progressive course over months to years, not an acute 2-day presentation 4

Core Diagnostic Features Present

This patient demonstrates all cardinal features required by the Confusion Assessment Method (CAM):

• Acute onset and fluctuating course: 2-day timeline with waxing and waning symptoms and periods of relative lucidity 1, 3

• Inattention: Easily distractible, reduced awareness of surroundings 1, 3

• Altered level of consciousness: Disorientation and confusion 1, 3

• Cognitive disorganization: Impaired recognition of family members, disorientation 1, 3

• Nighttime worsening: Classic sleep-wake cycle disturbance with symptoms worse at night 1, 2

Critical Clinical Pitfall

The most commonly missed presentation is hypoactive delirium, which carries higher mortality risk than hyperactive delirium and may present with cognitive slowing and sedated appearance that is mistakenly attributed to baseline dementia 2, 5. This patient's presentation could represent either hyperactive, hypoactive, or mixed delirium—all require urgent evaluation 1, 5.

Immediate Next Steps

Delirium represents a medical emergency that can be fatal if untreated 1, 3. The priority is identifying and treating underlying causes:

• Search for precipitating factors: Infection (urinary tract infection, pneumonia), metabolic derangements (hypoglycemia, electrolyte disturbances given her diabetes), dehydration, hypoxia, medications with anticholinergic properties, or acute organ failure 1, 6

• Obtain laboratory evaluation: Complete metabolic panel, complete blood count, urinalysis, chest radiograph 1

• Review all medications for potential culprits, particularly those with anticholinergic properties, sedatives, or opioids 1

• Assess hydration status and ensure adequate fluid intake, as dehydration is a common reversible cause 4, 1

Risk Factors Present

This patient has significant predisposing factors:

• Advanced age is the strongest risk factor for delirium 7, 8

• Hypertension and diabetes increase vulnerability to delirium through vascular mechanisms 8

• Approximately 20% of older adults on general medicine wards develop delirium 1