In a patient with Acute Mountain Sickness (AMS) and a history of atypical seizures, do you order an MRI (Magnetic Resonance Imaging) of the head?

MRI Head in Patients with AMS and History of Atypical Seizures

For patients with acute mountain sickness (AMS) and a history of atypical seizures, an MRI of the head should be ordered as it provides superior diagnostic information for neurological complications that may occur at high altitude.

Rationale for MRI in This Clinical Scenario

Understanding the Neurological Risks

• Patients with AMS can develop serious neurological complications, including high-altitude cerebral edema (HACE) in less than 1% of cases 1
• A history of atypical seizures represents a pre-existing neurological condition that may be exacerbated by altitude-related changes
• Neurological problems at high altitude can occur outside the setting of typical AMS, including seizures and focal neurological deficits 2

Diagnostic Approach Based on Guidelines

The ACR Appropriateness Criteria specifically directs clinicians to refer to the "Seizures and Epilepsy" criteria when evaluating patients with suspected seizure presenting with altered mental status 3. For patients with AMS and a history of seizures, this makes MRI particularly relevant because:

1. MRI offers superior detection of:

   • Small ischemic infarcts
   • Subtle cases of subarachnoid hemorrhage
   • Encephalitis
   • Focal cerebral edema 3

2. Research evidence shows:

   • Patients with seizures at high altitude may develop focal cerebral edema that can be detected on neuroimaging 2
   • Brain volume can increase by 0.8% to 2.7% after 16-32 hours at high altitude 4
   • Recent MRI studies have identified somatomotor network function as a predictor for AMS susceptibility 5

Clinical Decision Algorithm

When to Order MRI vs. CT:

1. Emergent situation with unstable patient:

   • Begin with non-contrast head CT (faster, more readily available)
   • Follow with MRI if the patient stabilizes and CT is negative or inconclusive

2. Stable patient with AMS and history of atypical seizures:

   • Proceed directly to MRI without contrast
   • Add contrast if there is concern for infection, tumor, or inflammatory conditions

Key Clinical Considerations:

• Severity of AMS symptoms: More severe symptoms (Lake Louise Score ≥5) increase the likelihood of neurological complications 1
• Timing: Neurological symptoms that persist or worsen after descent require more urgent imaging
• Associated symptoms: Presence of focal neurological deficits strongly indicates the need for MRI 3

Practical Challenges and Solutions

Challenges with MRI in This Population:

• Patients with AMS may have difficulty following commands
• Motion artifacts may compromise image quality
• Claustrophobia may be exacerbated by AMS symptoms 3

Solutions:

• Tailor examinations for shorter scan times
• Decrease the number of sequences to answer the specific clinical question
• Utilize motion-reducing sequences 3
• Consider sedation if absolutely necessary and safe given the patient's condition

Important Caveats

• MRI may be delayed or unavailable in remote high-altitude settings; in such cases, evacuation to lower altitude and CT imaging is the practical alternative 2
• The prevalence of AMS increases with altitude (13% increase for each 1000m rise above 2500m) 1, which should factor into clinical suspicion
• Coordination with the patient's managing physician and family members is critical for successful diagnostic imaging 3

By following this approach, clinicians can appropriately utilize MRI to evaluate patients with AMS and a history of atypical seizures, potentially identifying serious neurological complications that require specific management.