High Altitude Neurology

Abstract

Charles Clarke has managed to combine clinical neurological practice with high altitude mountaineering for over forty years. He was doctor on the successful Everest SW Face expedition in 1975 ("Everest The Hard Way") and on the NE Ridge of Everest in 1982. He has been on many other expeditions to the Great Ranges. He is an editor of Neurology: A Queen Square Textbook. This talk reviews neurological problems seen at high altitudes and their mechanisms. Neurology might seem of little relevance at 6000m, but this is the setting for high altitude cerebral edema (HACE) - a fatal consequence of chronic hypobaric hypoxia. Acute hypoxia causes light-headedness above 3500 m, and usually loss of consciousness above 5000m. Chronic hypoxia leads to Acute Mountain Sickness (AMS) - headache/malaise 6-24 hours above 3000m during acclimatisation, and HACE. HACE: In 1960 Charles Houston recognised high altitude pulmonary edema (HAPE). By 1970 it became clear that climbers could also develop headache, ataxia, papilledema and coma, the hallmarks of HACE. HACE and/or HAPE develop in 2% at 6000 m. In HACE, predeliction for the posterior brain circulation, seen on imaging and at autopsy remains unexplained. Rapid descent, and oxygen by mask or pressure bag and dexamethasone are effective HACE treatments. If mild HACE is treated promptly most cases resolve over several days. Once in coma, death is likely. Retinal haemorrhages: Altitude-related symptomless retinal haemorrhages were described in the 1970s. Occasionally, a florid retinopathy develops with visual loss. Stroke: Transient hemiparesis is sometimes seen with papilledema during HACE. Thrombotic infarction is presumed to cause more substantial hemiparesis: polycythemia, dehydration and cold probably contribute. Seizures, syncope, migraine, TIAs and funny turns: Occasionally an isolated seizure occurs when going high, but people whose epilepsy is well-controlled rarely have problems. In HACE, seizures are unusual. Syncope and near syncope are common during AMS. AMS can begin with a classical migraine. Transient aphasia has been noted. Other "funny turns", some probably non-epileptic attacks, are common. Other phenomena: Over 10 million people live around 4000m with few ill-effects. Chronic Mountain Sickness is fatigue/headache with polycythemia seen in high altitude residents. Permanent habitation is impossible above 6000 m. Deterioration is the steady decline in energy above 6500 m. Cognitive changes are common. Confusion and hallucinations occur above 8000 m.