What's the next step for a patient with slurred speech, gait disturbance, left-sided weakness, and autonomic symptoms (including bladder/bowel dysfunction), after a negative Computed Tomography (CT) head scan?

MRI Brain is the Next Step for a Patient with Neurological Deficits and Negative CT Head

For a patient presenting with slurred speech, gait disturbance, left-sided weakness, and autonomic symptoms (bladder/bowel dysfunction) who has had a negative CT head scan, an MRI of the brain is the most appropriate next diagnostic step.

Rationale for MRI Brain

The constellation of symptoms presented by this patient suggests a potentially serious neurological condition that requires further investigation despite the negative CT head. Here's why MRI is indicated:

1. CT Limitations: CT has excellent sensitivity for acute hemorrhage and bone abnormalities but limited sensitivity for many neurological conditions, particularly in the posterior fossa and brainstem.

2. Symptom Pattern: The combination of:

   • Slurred speech (dysarthria)
   • Gait disturbance
   • Unilateral weakness
   • Autonomic dysfunction (bladder/bowel symptoms)

   Suggests potential involvement of multiple neurological pathways that may not be visible on CT.

Clinical Decision Algorithm

Step 1: Evaluate CT Limitations

• CT head is highly sensitive for acute hemorrhage but has limited sensitivity for:
  • Posterior fossa lesions
  • Brainstem pathology
  • Early ischemic changes
  • Demyelinating disease
  • Small vascular lesions

Step 2: Consider Differential Diagnosis

Given the negative CT and symptom constellation:

• Stroke in areas poorly visualized by CT (brainstem, posterior circulation)
• Demyelinating disorders (multiple sclerosis, acute disseminated encephalomyelitis)
• Autoimmune encephalitis
• Space-occupying lesions in areas with limited CT sensitivity
• Spinal cord pathology (if symptoms suggest involvement)

Step 3: Proceed with MRI Brain

• MRI provides superior soft tissue contrast and can detect:
  • Small infarcts missed by CT
  • White matter lesions
  • Brainstem abnormalities
  • Demyelinating plaques
  • Subtle structural abnormalities

MRI Protocol Considerations

For this clinical presentation, the MRI protocol should include:

• T1 and T2-weighted sequences
• FLAIR (fluid-attenuated inversion recovery)
• DWI (diffusion-weighted imaging) to detect acute ischemia
• Gradient echo or susceptibility-weighted imaging for microhemorrhages
• With and without contrast if inflammatory or neoplastic process suspected

Additional Considerations

• Timing: MRI should be performed urgently given the constellation of neurological deficits
• Spinal Imaging: If brain MRI is negative or inconclusive, consider MRI of the cervical and thoracic spine, as the autonomic symptoms may suggest spinal cord involvement 1
• CSF Analysis: If MRI findings suggest inflammatory or infectious etiology, lumbar puncture may be warranted 2

Pitfalls to Avoid

1. Premature Closure: Don't assume a negative CT excludes serious pathology
2. Delayed Diagnosis: Waiting for clinical deterioration before advanced imaging can lead to worse outcomes
3. Incomplete Evaluation: Failing to consider both brain and spinal cord pathology when autonomic symptoms are present

The American College of Radiology Appropriateness Criteria recommends MRI when there is a stable or unchanged neurologic examination after unremarkable initial CT imaging in the setting of acute head trauma 2. Similarly, for patients with neurological symptoms and a negative CT, MRI is indicated to evaluate for conditions not well visualized on CT 2.