MRI of the Brain and Spine is the Next Best Step
For this patient with recurrent transient neurological symptoms (slurred speech, dysmetria, hypertonicity) lasting more than 6 hours with a prior similar episode, MRI of the brain and spine (Option B) is the most appropriate next diagnostic test. 1
Clinical Reasoning
This presentation strongly suggests a demyelinating process such as multiple sclerosis, given:
- Recurrent episodes of neurological dysfunction separated in time (months apart) 1
- Multiple anatomical locations suggested by symptoms (dysarthria suggests brainstem/cerebellar involvement; hypertonicity in legs suggests spinal cord involvement) 1
- Young patient with transient symptoms that partially or completely resolve 1
- Normal CT head, which is insensitive for detecting demyelinating lesions 2, 3
Why MRI is Superior to Other Options
MRI Detects What CT Cannot
- MRI is far more sensitive than CT for detecting acute infarcts, small ischemic lesions, demyelinating disease, and other subtle neurological pathologies 1, 2
- The American College of Radiology assigns MRI an appropriateness rating of 8/9 (usually appropriate) for patients with new focal neurological deficits lasting longer than 6 hours 1
- MRI detects early disease associated with increased water content, including multiple sclerosis, early infarcts, small tumors, and inflammatory lesions that CT misses 2, 3
Why Not the Other Options?
Option A (CSF oligoclonal bands): While oligoclonal bands support MS diagnosis, they should not be ordered before MRI imaging establishes the presence and distribution of CNS lesions 1. MRI findings guide whether lumbar puncture is even necessary.
Option C (EEG): This patient has no seizure activity or altered consciousness—EEG would not evaluate the structural lesions causing focal deficits like dysmetria and hypertonicity 4.
Option D (No further testing): This is inappropriate given recurrent neurological symptoms with objective findings on examination 1. Delaying appropriate imaging when neurological symptoms are present can miss treatable conditions 1.
Recommended MRI Protocol
- MRI brain without IV contrast as the initial study 1
- MRI spine (cervical and thoracic) to evaluate for spinal cord lesions causing leg hypertonicity 1
- Consider adding gadolinium contrast if demyelinating disease is confirmed, to assess for active inflammation 1
- Include MRA of head and neck (appropriateness rating 8/9) to evaluate for vascular abnormalities 1
Critical Pitfall to Avoid
Relying solely on CT imaging for transient neurological symptoms can miss subtle pathology, particularly small ischemic lesions and demyelinating plaques 1. The normal CT in this case does not exclude significant intracranial or spinal pathology 2, 3.