High altitude ataxia--its assessment and relevance.

Ataxia at altitude is reviewed in relation to acute mountain sickness (AMS). The cause of ataxia occurring at altitude is unknown but may be hypoxia affecting basal ganglia and hindbrain activity. Ataxia is an important sign of high altitude cerebral edema (HACE) but is less well-established as a clinical feature of AMS. Assessment of ataxia is part of the Environmental Systems and the Lake Louise questionnaires, together with a heel-to-toe measurement. More precise measures of ataxia include the Sharpened Romberg Test (SRT) and the use of unstable platforms. Isolated ataxia at altitude may not be related to AMS or HACE. Age affects ataxia and careful baseline measurements are essential in older subjects before results at high altitude can be interpreted. Testing for ataxia needs to be standardized with sufficient learning time. Ataxia should be distinguished from weakness or fatigue occurring at altitude. Specialized tests have not been shown to be clinically important. Our results above 5000 m showed that an abnormal SRT may be specific for AMS but with relatively poor sensitivity. Wobble board results have not correlated with AMS scores consistently. Other authors using an unstable platform in a chamber and static posturography during 3 days of exposure to 4559 m also found no relationship with AMS scores. Ataxia is a common and important clinical feature of HACE but is unhelpful in the assessment of mild or even moderate AMS in the absence of an altered mental state. The simple heel-to-toe test remains a useful part of the assessment of more severe AMS bordering on HACE.

The sharpened Romberg test for assessing ataxia in mild acute mountain sickness.

OBJECTIVE: To evaluate the Sharpened Romberg Test (SRT) as a measure of ataxia in subjects with mild acute mountain sickness in order to determine its sensitivity and specificity. METHODS: The SRT was performed in 23 subjects during ascent to 5260 m. RESULTS: The SRT was more often abnormal than the traditional heel-to-toe test, and at the highest altitude it was related to higher median Lake Louise symptom scores with predictive values of 60% sensitivity and 89% specificity. Our evaluation of the SRT appears to agree with similar studies on ataxia showing a lack of correlation between ataxia and symptoms of acute mountain sickness at altitudes below 5260 m. CONCLUSION: The SRT was easy to perform and provided a quantitative assessment of truncal ataxia in the field without the need for specialized equipment.

Ataxia at altitude measured on a wobble board.

OBJECTIVE: To establish a simple measure of ataxia for use at high altitude. METHODS: Twenty healthy subjects took part in a trek to 5005 m. At 5 different altitudes on the route, they undertook a balance test using a wobble board. The primary objectives were to investigate disturbances of ataxia at altitude and to correlate any observed disturbances with acute mountain sickness (AMS) scores. Secondary outcomes were correlations with cerebral regional oxygenation, pulse oximetry, and age. RESULTS: After a short learning curve, the wobble board test was found to be reproducible. Subjects over 31 years of age were significantly less steady than younger subjects. Subjects suffering acute mountain sickness scored significantly worse on the wobble board test, although scores did not correlate with a specific question on unsteadiness. A positive test defined as equal to or more than 2.5 contacts over 2 minutes gave a predictive value for acute mountain sickness of 66.7% at 4650 m and 100% at 5005 m. Cerebral regional oxygenation in 9 subjects at 5005 m correlated with the wobble board test (r = 0.73; p < .05), whereas pulse oximetry did not. CONCLUSIONS: The wobble board may be a useful adjunct in quantitating ataxia in the field. A positive result may indicate the presence of AMS and may be a useful clinical measure of cerebral hypoxia but should be correlated with other clinical features.