HACE is caused by the swelling of the brain from the dilation of the oxygen starved blood vessels and fluid leakage.
The first symptom of HACE is loss of balance and muscular coordination, scientifically known as ataxia, this can progress to loss of mental function, hallucination, weakness on one side of the body and blurred vision.
The symptoms can develop over a few hours to a couple of days, a headache and nausea or vomiting are also very common amongst sufferers of HACE in addition to the combined symptoms of HAPE and if left untreated, HACE can become very serious leading to a coma and/or death.
Furthermore, a fast rate of ascent and extreme exertion can cause HAPE or HACE to develop suddenly without the progression from AMS.
The risk factors associated with HACE could also affect much younger people, as there is less space within their skull for brain swelling to occur or in those who suffer head injuries at altitude.
The treatments for HACE are very similar to those of HAPE:
Barry, P.W. and Pollard, A.J. (2003) “Altitude illness”, British Medical Journal, 326(7395), pp.915-919.
Bezruchka, S. (2005) Altitude illness: Prevention & Treatment, Seattle: Mountaineers Books.
Luks, A.M., Auerbach, P.S., Freer, L., Grissom, C.K., Keyes, L.E., McIntosh, S.E., Rodway, G.W., Schoene, R.B., Zafren, K. and Hackett, P.H. (2019) “Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update”, Wilderness & environmental medicine, 30(4), pp.3-18.