What is the next best step for a 31-year-old woman presenting to the emergency department with slurred speech that began approximately six hours ago, with a history of a similar episode a few months ago, and normal initial lab results and non-contrast computed tomography (CT) of the head?

Magnetic Resonance Imaging is the Most Appropriate Next Step for a Patient with Recurrent Transient Neurological Symptoms

Magnetic resonance imaging (MRI) of the brain and spine is the most appropriate next diagnostic test for this 31-year-old woman presenting with recurrent episodes of slurred speech.

Clinical Presentation Analysis

• The patient presents with slurred speech that began 6 hours ago, with a similar episode occurring a few months prior that resolved within 12 hours 1
• Initial workup including comprehensive metabolic panel, complete blood count, and non-contrast CT head were all normal 1
• The patient has mild dysarthria and mild ataxia in the legs on examination, which are focal neurological deficits 1

Diagnostic Approach for Transient Neurological Symptoms

Why MRI is the Appropriate Next Step:

• MRI is more sensitive than CT for detecting acute infarcts, small ischemic lesions, demyelinating disease, and other subtle neurological pathologies 1
• For patients with new focal neurological deficits lasting longer than 6 hours, MRI head without IV contrast has an appropriateness rating of 8/9 (usually appropriate) according to ACR guidelines 1
• The clinical presentation is consistent with a possible transient ischemic attack (TIA) or minor stroke, for which MRI has superior diagnostic yield compared to CT 2
• In patients with transient or minor neurological symptoms, MRI evidence of acute ischemia was found in 17-31% of cases depending on clinical probability of TIA/stroke 2

Why Other Options Are Less Appropriate:

• Cerebrospinal fluid oligoclonal band screening (option 1) would be appropriate if multiple sclerosis was strongly suspected, but MRI should be performed first to detect white matter lesions before proceeding to lumbar puncture 3
• Electroencephalogram (option 3) would be appropriate if seizures were suspected, but the clinical presentation of recurrent, self-limited slurred speech with ataxia is more consistent with a cerebrovascular or demyelinating etiology 1
• "Other studies" (option 4) is vague but would be less appropriate than MRI given the clinical presentation 1

Specific MRI Protocol Recommendations

• MRI brain without IV contrast should be performed as the initial MRI study 1
• Consider adding MRI brain with IV contrast if demyelinating disease, infection, or tumor is suspected 1
• Include MRA (magnetic resonance angiography) of the head and neck to evaluate for vascular abnormalities, as this has an appropriateness rating of 8/9 for patients with TIA symptoms 1
• A combined fast MRI protocol with MRA has been shown to provide equivalent or better information compared to CT angiography in 95% of cases with acute neurological presentations 4

Clinical Implications of Imaging Findings

• MRI can detect small ischemic lesions that may be missed on CT, which is crucial as 70% of patients with missed ischemic stroke diagnoses presented with altered mental status 1
• The presence of MRI evidence of acute brain ischemia is associated with a significantly increased risk of subsequent stroke (age-adjusted hazard ratio 13) 2
• If multiple sclerosis is suspected, the presence of white matter lesions on MRI at presentation with a clinically isolated syndrome is a powerful predictor of progression to clinically definite multiple sclerosis 3

Common Pitfalls to Avoid

• Relying solely on CT imaging for transient neurological symptoms can miss subtle pathology, particularly small ischemic lesions 1
• Delaying appropriate imaging when neurological symptoms are present can miss treatable conditions 5
• Failing to consider vascular imaging (MRA) in addition to parenchymal imaging in patients with focal neurological deficits 1

MRI is the most sensitive imaging modality for evaluating the patient's presentation and should be the next step in the diagnostic workup.