Chronic mountain sickness (CMS) is a disease that can develop during extended time living at altitude. It is also known as 'Monge’s disease' , after its first description in 1925 by Carlos Monge. While acute mountain sickness is experienced shortly after ascent to high altitude, chronic mountain sickness may develop after many years of living at high altitude. In medicine, high altitude is defined as over 2500 metres, but most cases of CMS occur at over 3000 m.

CMS is characterised by polycythemia

Polycythemia

Polycythemia is a disease state in which the proportion of blood volume that is occupied by red blood cells increases...

 (increased hematocrit

Hematocrit

The hematocrit or packed cell volume or erythrocyte volume fraction is the percentage of the concentration of red blood cells in blood. It is normally about 45% for men and 40% for women...

) and hypoxemia

Hypoxemia

Hypoxemia is generally defined as decreased partial pressure of oxygen in blood, sometimes specifically as less than or causing hemoglobin oxygen saturation of less than 90%.-Distinction from anemia and hypoxia:...

 which both decrease on descent from altitude. CMS is believed to arise because of an excessive production of red blood cells, which increases the oxygen carrying capacity of the blood but may cause increased blood viscosity and uneven blood flow through the lungs (V/Q mismatch). However, CMS is also considered an adaptation of pulmonary and heart disease to life under chronic hypoxia at altitude.

The most frequent symptoms and signs of CMS are headache, dizziness, tinnitus

Tinnitus

Tinnitus |ringing]]") is the perception of sound within the human ear in the absence of corresponding external sound.Tinnitus is not a disease, but a symptom that can result from a wide range of underlying causes: abnormally loud sounds in the ear canal for even the briefest period , ear...

, breathlessness, palpitations, sleep disturbance, fatigue, anorexia

Anorexia (symptom)

Anorexia is the decreased sensation of appetite...

, mental confusion, cyanosis

Cyanosis

Cyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...

, and dilation of veins.

Clinical

Clinical research

Clinical research is a branch of medical science that determines the safety and effectiveness of medications, devices, diagnostic products and treatment regimens intended for human use...

 diagnosis by laboratory indicators have ranges of: Hb

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 > 200 g/L, Hct

Hematocrit

The hematocrit or packed cell volume or erythrocyte volume fraction is the percentage of the concentration of red blood cells in blood. It is normally about 45% for men and 40% for women...

 >65%, and arterial oxygen saturation (SaO2) <85% in both genders.

Treatment involves descent from altitude, where the symptoms will diminish and the hematocrit return to normal slowly. Acute treatment at altitude involves bleeding (phlebotomy

Phlebotomy

Phlebotomy is the process of making an incision in a vein.It is associated with the following concepts:* Venipuncture, the practice of collecting venous blood samples* The main practice of a phlebotomist, an individual trained to draw blood...

), removal of circulating blood, to reduce the hematocrit; however this is not ideal for extended periods.