Scoring System for Acute Mountain Sickness and High-Altitude Cerebral Edema
The Lake Louise Scoring System is the recommended and validated tool for assessing acute mountain sickness (AMS), using a self-assessment questionnaire that rates four key symptoms (headache, nausea, dizziness, and fatigue) on a 0-3 severity scale, with a total score ≥5 indicating AMS 1.
Lake Louise Scoring System Components
The scoring system evaluates symptom severity as follows:
- 0 = no discomfort
- 1 = mild symptoms
- 2 = moderate symptoms
- 3 = severe symptoms
Four symptoms assessed:
- Headache
- Nausea/vomiting
- Dizziness/lightheadedness
- Fatigue/weakness
Diagnostic threshold: Total score ≥5 indicates AMS 1
Alternative Scoring Methods
While the Lake Louise Score is the gold standard, several alternative instruments exist:
AMS-Cerebral Score (AMS-C)
- Part of the Environmental Symptoms Questionnaire
- Threshold: ≥0.7 indicates AMS
- Performs similarly to Lake Louise Score but is less commonly used 2, 3
Clinical Functional Score (CFS)
- Simplest single-question assessment: "Overall if you had any symptoms, how did they affect your activity?"
- Ordinal scale 0-3
- Threshold: ≥2 (moderate to severe reduction in daily activities) indicates AMS
- Positive likelihood ratio 3.2, specificity 67% 2
- Most practical for clinical and travel settings due to its simplicity
Comparative Performance
Research demonstrates that the Lake Louise Score, AMS-C, and CFS perform similarly when validated against each other, with positive likelihood ratios ranging from 3.2-8.2 and sensitivities of 67%-82% 2. The Lake Louise Score shows 78% sensitivity and 93% specificity when using a cutoff >4, and is more effective than the AMS-C score across different altitudes 3.
High-Altitude Cerebral Edema (HACE) Assessment
HACE represents the severe, life-threatening end of the AMS spectrum 1. While AMS and HACE exist on a continuum, HACE is diagnosed clinically rather than by scoring system:
Clinical criteria for HACE:
- Presence of AMS symptoms
- Ataxia (inability to walk heel-to-toe in a straight line)
- Altered consciousness (confusion, lethargy, or coma)
- May include retinal hemorrhages (uncommon) 4
Critical distinction: Only 1% of AMS cases progress to HACE, but HACE carries 50% mortality if untreated 1.
Special Population: Preverbal Children
For children aged 3-36 months, use the Children's Lake Louise AMS Score (CLLS) 5:
- Combines a "fussiness score" (headache equivalent) with a pediatric symptom score
- Assesses appetite, vomiting, playfulness, and sleep ability
- Diagnostic threshold: CLLS ≥7 with fussiness score ≥4 and pediatric symptom score ≥3
Practical Application Algorithm
Initial screening: Use Lake Louise Score questionnaire (most validated) or CFS (simplest single question) 1, 2
If score suggests AMS (≥5 on Lake Louise or ≥2 on CFS):
- Assess for HACE warning signs (ataxia, altered consciousness)
- If HACE suspected: immediate descent and emergency treatment
- If isolated AMS: halt ascent, consider descent, symptomatic treatment
Timing of assessment:
- Assess on day of ascent
- Reassess the following morning as AMS prevalence increases overnight, particularly at altitudes ≥3650m 6
Important Caveats
- Altitude-dependent prevalence: AMS affects 5.8% at 2850m but increases to 21.9% at 4559m on day of ascent 6
- The Lake Louise Score may be normal in some HACE cases; clinical judgment supersedes scoring 4
- MRI findings do not correlate with AMS severity—diagnosis remains clinical 7
- Women may have statistically higher AMS risk and should undergo systematic screening 1