Chronic Mountain Sickness (CMS), also known as Monge’s disease, affects individuals who have lived at high altitudes for extended periods. This condition is characterized by an excessive production of red blood cells, which can lead to various health complications. It was first described in 1925 by Carlos Monge Medrano, a Peruvian physician who specialized in high-altitude illnesses.
The Body’s Adaptation and Maladaptation to High Altitude
High altitudes present a challenge due to reduced atmospheric pressure and lower oxygen availability, a condition known as hypoxia. The body typically responds through acclimatization, involving physiological adjustments like an increased breathing rate and enhanced red blood cell production to improve oxygen transport.
In individuals with Chronic Mountain Sickness, however, this adaptive process becomes maladaptive. The body overcompensates for the lack of oxygen, leading to an excessive increase in red blood cells, known as polycythemia or excessive erythrocytosis (EE). This results in thicker blood, which can hinder blood flow and oxygen delivery to various organs and tissues. This maladaptive response is believed to arise partly due to a blunted ventilatory response to hypoxia, meaning the body does not increase breathing sufficiently to compensate for low oxygen.
Identifying Chronic Mountain Sickness
Individuals living at high altitudes for many months or years, typically above 2,500 meters (approximately 8,200 feet), are susceptible to Chronic Mountain Sickness. This includes native populations and those returning to high altitude after living at lower elevations. The excessive red blood cell count in CMS contributes to numerous symptoms by making the blood thicker and increasing its viscosity.
Common symptoms include severe fatigue, breathlessness, and headaches. Other signs are dizziness, sleep disturbances, including central sleep apnea, and a bluish discoloration of the lips and skin, known as cyanosis. Cognitive impairment, such as mental confusion, is also frequently reported. Less common symptoms can include tinnitus, palpitations, loss of appetite, and dilation of veins.
Diagnosis of CMS typically involves a clinical assessment of symptoms combined with blood tests to confirm polycythemia. A high hematocrit level, which is the proportion of blood volume occupied by red blood cells, is a key indicator. For instance, diagnostic criteria often include a hemoglobin concentration of 21 g/dL or more for males and 19 g/dL or more for females, along with an arterial oxygen saturation (SaO2) below 85% in both sexes. Additionally, a “Monge’s disease score” or similar clinical guidelines, such as the Qinghai questionnaire, are used to evaluate the presence and severity of associated symptoms. These scores consider a minimum number of symptoms, including breathlessness, palpitations, sleep disturbances, cyanosis, and headaches, to support the diagnosis.
Managing and Preventing Chronic Mountain Sickness
The most effective approach for managing Chronic Mountain Sickness is descent to a lower altitude. Moving to an environment with increased oxygen availability often leads to a gradual disappearance of symptoms and a return of hematocrit levels to a more typical range. Complete recovery can take several months, and individuals generally need to remain at lower altitudes for sustained relief.
For those who cannot permanently descend, other management strategies are available. Supplemental oxygen therapy can help increase oxygen levels in the blood, reducing strain on the body and improving symptoms like shortness of breath and fatigue. This therapy supports better oxygenation of the body’s tissues and organs.
Medications such as acetazolamide are also used. Acetazolamide can help with acclimatization by inducing a mild metabolic acidosis, which stimulates breathing and increases arterial oxygen content, thereby reducing hypoxemia. It can also help reduce red blood cell production and improve symptoms like headaches.
Another treatment option is phlebotomy, or bloodletting, which involves periodically removing blood to reduce the red blood cell count and blood viscosity. While phlebotomy offers temporary relief, it is not a long-term solution. In some cases, nifedipine or phosphodiesterase-5 inhibitors like sildenafil may be used to address pulmonary hypertension, a potential complication of CMS.
Preventive measures for CMS focus on gradual acclimatization when moving to high altitudes. This involves ascending slowly, allowing the body time to adapt to lower oxygen levels. For instance, avoiding direct ascent to a sleeping altitude above 2,750 meters (approximately 9,000 feet) in a single day is recommended. Once above 3,000 meters (9,850 feet), it is advisable to increase sleeping altitude by no more than 500 meters (1,600 feet) per day, with an extra acclimatization day for every 1,000 meters (3,300 feet) of elevation gain. Additionally, avoiding rapid re-ascent after a period at low altitude and undergoing regular medical check-ups for long-term high-altitude residents can help in early detection and management.