Is imaging and EEG an appropriate next step for a patient with a history of recurrent stroke, diabetes, and chronic kidney disease presenting with delirium without fever and normal blood tests, including complete blood counts (CBC), electrolyte levels, and stable renal function?

Imaging and EEG in Delirium with Recurrent Stroke History

Yes, brain imaging is appropriate and should be performed, specifically a non-contrast head CT as the first-line test, given this patient's high-risk profile with recurrent stroke history. 1 EEG should be obtained if there is suspicion for non-convulsive seizures or if the delirium persists despite initial management. 1, 2

Rationale for Brain Imaging

This patient falls into a high-risk category that warrants neuroimaging despite normal laboratory values:

• History of recurrent stroke is one of the four strongest risk factors for delirium in the emergency department setting, making intracranial pathology more likely. 1

• Non-contrast head CT is the first-line imaging modality and should be performed unless the etiology is clearly non-neurologic and the risk of intracranial pathology is definitively low. 1

• The most common neurological diagnoses causing altered mental status in the emergency department are intracranial hemorrhage and ischemic stroke. 1

• 70% of patients with missed ischemic stroke diagnoses present with altered mental status rather than focal deficits, making imaging critical even without obvious neurologic signs. 1, 3

Expected Yield and Clinical Context

• While the overall yield of head CT in delirium is relatively low (2.7% positive findings in hospitalized medical patients without trauma or focal deficits), 4 this patient's recurrent stroke history substantially increases pre-test probability. 1

• The three-day duration of symptoms does not exclude acute intracranial pathology, as subacute processes including evolving infarcts, delayed hemorrhagic transformation, or subdural hematomas can present in this timeframe. 1

Role of MRI Brain

If the initial head CT is unrevealing and delirium persists, MRI brain without contrast should be obtained as a second-line test. 1, 3

• MRI has higher sensitivity for detecting small ischemic infarcts, which are frequently missed on CT and commonly present with altered mental status alone. 1, 3

• In patients with delirium and recurrent stroke history, MRI can identify subdural hematoma, subtle subarachnoid hemorrhage, encephalitis, meningitis, or small infarcts that explain the clinical picture. 1

• MRI leads to changes in clinical management in 76% of patients with acute disorders of consciousness, including revised diagnoses (20%), revised levels of care (21%), and improved prognostication (33%). 1, 3

Optimal MRI Protocol

If MRI is pursued, the protocol should include: 3

• Diffusion-weighted imaging (DWI) to identify acute ischemic changes
• T2 gradient-echo or susceptibility-weighted imaging (SWI)* to detect microhemorrhages
• FLAIR sequences to evaluate for subtle edema or vascular changes
• MR angiography may be considered given the recurrent stroke history to assess for progressive vasculopathy

Role of EEG

EEG is appropriate in specific clinical scenarios but is not routinely indicated as a first-line test for all delirium cases. 1, 2

When to Order EEG

• If non-convulsive status epilepticus is suspected - this is the only test that can definitively identify ongoing epileptic activity causing confusion. 2

• If delirium persists despite treatment of identified causes - EEG can help differentiate organic from functional etiologies and monitor severity. 2, 5

• To assess severity and monitor therapeutic response - the degree of EEG changes correlates with encephalopathy severity. 2, 5

Expected EEG Findings

In delirium, EEG typically shows: 5

• Slowing or dropout of the posterior dominant rhythm
• Generalized theta or delta slow-wave activity
• Poor organization of background rhythm
• Loss of reactivity to eye opening and closing
• A normal EEG makes delirium very unlikely 6

Limitations of EEG

• EEG is time-consuming and may have variable interpretation in the acute setting. 6
• Specificity can be limited, particularly distinguishing delirium from dementia or normal aging changes. 5
• EEG should not delay urgent neuroimaging when intracranial pathology is suspected. 1

Clinical Algorithm

1. Obtain non-contrast head CT immediately given recurrent stroke history, diabetes, and chronic kidney disease. 1

2. If CT is negative and delirium persists beyond 24-48 hours or worsens, obtain MRI brain without contrast with DWI, SWI, and FLAIR sequences. 1, 3

3. Consider EEG if:

   • Subtle seizure activity is suspected (myoclonic jerks, eye deviation, automatisms)
   • Delirium persists despite addressing metabolic and infectious causes
   • There is fluctuating level of consciousness suggesting possible non-convulsive status epilepticus 2, 6

Critical Pitfalls to Avoid

• Do not defer imaging based solely on normal laboratory values - intracranial pathology can occur with normal blood tests. 1

• Do not assume delirium is purely metabolic in a patient with recurrent stroke history, even without focal deficits. 1, 3

• Do not order contrast-enhanced CT as first-line - it adds no value over non-contrast CT for acute evaluation. 1

• Be aware that chronic kidney disease may limit contrast-enhanced studies if needed later, making non-contrast protocols even more important initially. 1