MRI of the Brain and Spine is the Next Best Step
Given this patient's recurrent transient neurological symptoms (slurred speech, dysmetria, hypertonicity) with a prior similar episode that resolved spontaneously, and an unremarkable CT scan, you should order MRI of the brain and spine now (Option B). This presentation is highly suggestive of a demyelinating process such as multiple sclerosis, and MRI is essential for detecting the characteristic lesions that CT cannot visualize 1.
Clinical Reasoning
Why MRI is the Appropriate Next Step
The American College of Radiology recommends MRI for patients with new focal neurological deficits lasting longer than 6 hours, with an appropriateness rating of 8/9 (usually appropriate) 1. This patient's symptoms began six hours ago and have not resolved.
MRI is far more sensitive than CT for detecting acute infarcts, small ischemic lesions, demyelinating disease, and other subtle neurological pathologies 1, 2, 3. The unremarkable CT does not exclude significant pathology in this clinical context.
The combination of recurrent transient symptoms, mild cerebellar signs (dysmetria), and upper motor neuron signs (hypertonicity in legs) strongly suggests demyelinating disease 1. These disseminated neurological findings separated in time and space are classic for multiple sclerosis.
MRI of both brain AND spine is specifically indicated here because spinal cord lesions are common in demyelinating disease and may explain the leg hypertonicity 1. The American College of Radiology guidelines support comprehensive imaging in this scenario.
Why Other Options Are Inappropriate Now
Cerebrospinal fluid oligoclonal band screening (Option A) is premature without first obtaining MRI evidence of demyelinating lesions 1. The diagnostic workup for suspected demyelinating disease begins with imaging, not lumbar puncture. CSF analysis may be considered later if MRI findings are equivocal.
Electroencephalogram (Option C) would be appropriate if seizure were suspected, but this patient has no features suggesting seizure activity (no loss of consciousness, no postictal confusion, no tongue biting) 4. The focal neurological deficits and their persistence argue against a postictal state.
No further testing (Option D) is inappropriate and potentially dangerous. This patient has ongoing neurological deficits that have persisted for six hours with a history of a prior similar episode 1. Failure to pursue appropriate imaging could miss treatable conditions including stroke, demyelinating disease, or other serious pathology 1.
Critical Pitfalls to Avoid
Do not rely solely on CT imaging for transient neurological symptoms, as it can miss subtle pathology, particularly small ischemic lesions and demyelinating plaques 1, 2, 3. MRI detects 70% of strokes that present with altered mental status that CT misses 4.
Do not delay appropriate imaging when neurological symptoms are present and persistent 1. The six-hour duration and lack of improvement in the ED mandate further investigation.
Do not assume transient symptoms that resolved previously are benign 1. The recurrent nature of this patient's symptoms with a prior episode months ago that resolved in less than 12 hours is a red flag for demyelinating disease with relapsing-remitting pattern.