Chronic mountain sickness

Chronic mountain sickness (CMS) is a disease in which the proportion of blood volume that is occupied by red blood cells increases (

CMS was first described in 1925 by Carlos Monge Medrano, a Peruvian doctor who specialised in diseases of high altitude.^[3] While acute mountain sickness is experienced shortly after ascent to high altitude, chronic mountain sickness may develop only after many years of living at high altitude. In medicine, high altitude is defined as over 2,500 metres (8,200 ft), but most cases of CMS occur at over 3,000 metres (9,800 ft).

It has recently been correlated with increased expression of the genes ANP32D and SENP1.^[4][5]

Diagnosis

CMS is characterised by

Migration to low altitude is curative, though not immediate, as the body adapts to the normal oxygen level near sea-level and the haematocrit normalises. Alternatively, bloodletting (phlebotomy) can be performed to lower the haematocrit temporarily; when combined with volume replacement with fluids this can have a longer effect.^[1]

Medication with acetazolamide, a carbonic anhydrase inhibitor, has been shown to improve chronic mountain sickness by reducing erythropoietin and the resulting polycythaemia, which results in better arterial oxygenation and a lower heart rate.^[7]

Oxygen therapy and training in slow breathing techniques has been shown to reduce symptoms through increasing blood oxygenation.^[1]

Epidemiology

Although CMS generally affects people native to altitudes higher than 3,000 metres (9,800 ft), it does not affect populations around the world equally. A 2013 study

• Ethiopia [3600–4100 m]: 0%
• Tibetan Plateau (Tibetans): 0.91–1.2%
• Indian Himalayas [3000–4200 m]: 4–7%
• Kyrgyzstan [3000–4200 m]: 4.6%
• Tibetan Plateau (Han Chinese): 5.6%
• La Paz, Bolivia [3600 m]: 6–8%
• Bolivia: 8–10%
• Cerro de Pasco, Peru [4300 m]: 14.8–18.2%

References