Chronic mountain sickness

Introduction

Chronic mountain sickness (often abbreviated as CMS and sometimes called Monge’s disease) is a condition that affects people who live at high altitudes for long stretches of time. It’s not the same as the acute altitude sickness you might get on a trek; instead, it sneaks up gradually, sometimes over years, and can seriously impact daily life—think headaches, breathlessness, fatigue and a host of other issues. While it’s especially common above 2,500–3,000 meters, you can see cases even in folks who’ve moved back to lower elevation but still carry the adaptations. In this article, we’ll look at what chronic mountain sickness is, why it happens, typical symptoms, how it’s diagnosed, and what treatment and prevention options exist—plus a realistic outlook.

Definition and Classification

Medically speaking, chronic mountain sickness is characterized by an excessive number of red blood cells (polycythemia) and reduced oxygen saturation in arterial blood, developing in long-term high-altitude residents. It’s classified as a form of high altitude illness, distinct from acute mountain sickness, high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). Clinicians divide CMS into mild, moderate, and severe based on hemoglobin levels (males > 21 g/dL, females > 19 g/dL in severe cases) and symptom burden.

Broadly you can think of these categories:

• Type I (Benign CMS): moderate polycythemia, mild symptoms (headache, dizziness)
• Type II (Progressive CMS): severe erythrocytosis, significant hypoxemia, right-heart strain

The primary system involved is the cardiopulmonary system—lungs, heart, blood vessels—and secondarily the brain if low oxygen persists.

Causes and Risk Factors

Understanding the causes of CMS means diving into how our bodies adapt to lower oxygen (hypoxia) at altitude. Usually, newcomers get a boost in breathing rate and red blood cell production to carry more oxygen. But in some long-term settlers, that RBC boost goes too far: thickened blood, sluggish flow, and chronic hypoxemia. Here’s what we know:

• Genetic predisposition: Certain ethnic groups (e.g., Andean highlanders) show higher rates; variants in genes like EPAS1 and EPO can influence RBC production.
• Environmental factors: Altitudes above 3,000 m seem critical, though CMS can occur as low as 2,500 m. Seasonal cold, indoor smoke from cooking, or poor ventilation may worsen hypoxia.
• Lifestyle contributors: Smoking, alcohol misuse, even heavy physical work in cold weather can exacerbate oxygen depletion.
• Infectious/inflammatory triggers: Chronic lung infections (e.g., TB sequelae) or repeated pneumonia can damage lung tissue, reducing oxygen exchange.
• Autoimmune/inflammatory links: There’s emerging research that low‐grade inflammation of small pulmonary vessels might play a role but it’s still under study.

Non-modifiable risks include age (peak in middle age), sex (men often more affected though female rates rise post-menopause), and genetic background. Modifiable factors are about improving living conditions, reducing indoor pollution, and addressing smoking or chronic lung disease. Yet some causes—like complex gene-environment interplay—remain not fully understood, so ongoing research is key.

Pathophysiology (Mechanisms of Disease)

To get the biology right, picture normal high-altitude adaptation: low oxygen triggers increased breathing (hyperventilation) and spikes in erythropoietin (EPO) which in turn ramps up red blood cell (RBC) production. In chronic mountain sickness, this adaptation overshoots. Here’s the chain of events:

• Persistent Hypoxia: Incomplete ventilation-perfusion matching in lungs leads to low arterial oxygen pressure (PaO₂).
• Excess Erythropoiesis: The kidneys sense the low PaO₂, crank out more EPO, bone marrow goes into overdrive, producing too many RBCs.
• Blood Viscosity Rise: Excess RBCs thicken the blood (hyperviscosity), slowing circulation, increasing workload on the heart, especially the right ventricle.
• Pulmonary Hypertension: The small pulmonary arteries constrict in hypoxia (hypoxic pulmonary vasoconstriction), raising pulmonary arterial pressure, potentially leading to right-heart hypertrophy or failure.
• Reduced Cardiac Output: Over time, the heart can't keep up; tissues get even less oxygen.
• Neurovascular Effects: Chronic low O₂ may slightly impair cognitive function—subtle memory lapses, difficulty concentrating, mood swings—and even increase migraine risk.

It’s a vicious cycle: low oxygen → more RBCs → thick blood → poorer flow → even lower tissue oxygenation. At the cellular level, oxidative stress and endothelial dysfunction contribute as well, though we’re still piecing together those molecular details.

Symptoms and Clinical Presentation

Symptoms of chronic mountain sickness evolve gradually, often over years. In the early phase, a person may feel almost normal except for mild headaches or breathlessness when walking uphill. But with time these become more pronounced:

• Neurological: Persistent headache (often throbbing, worse in the morning), dizziness, tinnitus ("ringing in ears"), possible sleep disturbances such as frequent awakenings or restless legs.
• Cardiorespiratory: Shortness of breath with minimal exertion; chest tightness; palpitations; cough (sometimes productive if there’s associated inflammation).
• Hematological: Noticeably ruddy complexion; splenomegaly (tender, enlarged spleen); fatigue due to sluggish circulation.
• General discomfort: Lethargy, weakness, poor exercise tolerance, decreased appetite and unintentional weight loss.

As CMS advances, you might see:

• Polycythemia vera–like features: extreme fatigue, headaches becoming daily, impaired judgment, even mild cognitive decline.
• Signs of right-heart strain: swollen ankles, jugular venous distension, hepatic congestion.
• Warning signs (urgent): chest pain at rest, fainting spells, sudden worsening shortness of breath, confusion—these could indicate impending heart failure or severe hypoxemia and warrant immediate medical attention.

Individual variability is high: some residents at 4,000 m barely notice, while others at 2,600 m develop severe CMS. Fun fact: I once spoke to a yak-herder in Tibet who shrugged and said “it’s part of life here,” but then later admitted he’d lost 5 kg over months and struggled to breathe walking to village markets.

Diagnosis and Medical Evaluation

Diagnosing CMS relies on combining clinical findings, lab tests, and sometimes imaging. A typical workup might include:

• Medical history & physical exam: Ask about duration at altitude, symptom onset, pre-existing lung/cardiac disease. Look for ruddy skin, cyanosis, clubbing, splenomegaly.
• Pulse oximetry: Resting SpO₂ below ~85–90% is suspicious in a long-term resident.
• Complete blood count (CBC): Elevated hemoglobin and hematocrit beyond normal for altitude (e.g., Hb > 18.5 g/dL for women, > 19.5 g/dL for men; cutoffs vary by guideline).
• Arterial blood gas (ABG): Low PaO₂, sometimes elevated CO₂ if ventilatory drive is blunted.
• Cardiac evaluation: ECG, echocardiography to assess right-heart pressures, look for pulmonary hypertension.
• Chest imaging: Chest X-ray or CT to rule out other lung pathology (e.g., TB sequelae, interstitial disease).
• Sleep study (polysomnography): Occasionally done to see if sleep-disordered breathing (periodic breathing or apnea) is worsens hypoxia at night.

Differential diagnoses include polycythemia vera (primary bone marrow problem), chronic obstructive pulmonary disease (COPD), congenital heart disease, and secondary causes of erythrocytosis like smoking or EPO-producing tumors. Typically, the diagnostic pathway starts in primary care or a local health post and may lead to specialist referral.

Which Doctor Should You See for Chronic Mountain Sickness?

If you suspect chronic mountain sickness, the first point of contact is usually a primary care physician or family doctor—especially if you’re in a high-altitude region. They’ll do initial tests like CBC and pulse oximetry. From there, you might be referred to:

• Pulmonologist: specialist for lung-related aspects, hypoxemia, pulmonary hypertension.
• Cardiologist: if right-heart strain or arrhythmias are present.
• Hematologist: for complex cases of severe polycythemia requiring therapeutic phlebotomy or cytoreductive therapy.

Wondering “who to consult online”? Telemedicine platforms can help with initial guidance—interpreting your CBC results, suggesting when to see a specialist, or clarifying overnight oximetry patterns. Still, telehealth is a supplement: you’ll need in-person exams for accurate blood draws, echocardiograms or urgent care if you have warning signs like chest pain or syncope. In emergencies, call local services—no video chat can replace urgent oxygen or phlebotomy.

Treatment Options and Management

Treating CMS blends reducing red blood cell mass, improving oxygenation, and addressing symptoms. Key strategies include:

• Phlebotomy: periodic blood removal to lower hematocrit—classic, effective but can cause iron deficiency if overdone.
• Oxygen therapy: home-based nocturnal oxygen for those with severe hypoxemia (< 80% SpO₂), improves sleep quality and cognitive symptoms.
• Medications: ex. acetazolamide to stimulate ventilation; some studies explore drugs targeting pulmonary hypertension (e.g., sildenafil) but data is modest.
• Lifestyle adjustments: stop smoking, reduce indoor smoke exposure, balanced nutrition (avoid iron supplements except under hematologist guidance), moderate exercise.
• Descent: moving to lower altitude is the most definitive “cure,” but not always feasible due to socioeconomic or cultural reasons.

First-line therapy is typically phlebotomy plus oxygen; advanced cases may need combined drug approaches or even airplane evacuation to low altitude. Always weigh benefits vs side effects (e.g., phlebotomy-caused anemia, acetazolamide-induced paresthesia).

Prognosis and Possible Complications

The outlook for chronic mountain sickness varies. Mild CMS often stabilizes if managed well, but severe untreated cases can develop serious complications:

• Pulmonary hypertension & right-heart failure: chronic high pulmonary pressure strains the heart, leading to congestive symptoms.
• Thrombotic events: thickened blood poses risk for clots—deep vein thrombosis or rarely pulmonary embolism.
• Cognitive impairment: persistent hypoxia may subtly affect memory and executive function.
• Reduced quality of life: fatigue, poor sleep, exercise intolerance can impact work, social activities, and mental health.

Factors influencing prognosis include how early you diagnose, access to treatment (oxygen, phlebotomy), and ability to modify risk factors. Those who relocate to lower elevations often see rapid symptomatic relief, though some vascular changes may persist.

Prevention and Risk Reduction

Preventing CMS focuses on minimizing chronic hypoxia and controlling excessive erythropoiesis. Strategies include:

• Gradual ascent & acclimatization: for newcomers or workers, avoid rapid moves above 2,500 m; allow weeks-months for adaptation.
• Living conditions: proper ventilation, reduce indoor smoke from cookfires, use clean-burning stoves.
• Periodic health checks: regular CBC and SpO₂ monitoring in high-altitude communities, catch rising hematocrit early.
• Diet & lifestyle: balanced diet rich in antioxidants, moderate exercise avoiding extreme exertion, no smoking or heavy alcohol.
• Medical prophylaxis: low-dose acetazolamide or intermittent oxygen in those with borderline saturation—discuss with a specialist.

Screening programs in Himalayan or Andean villages can detect early polycythemia and guide interventions. That said, not all CMS is preventable—genetic factors and socioeconomic barriers play a role.

Myths and Realities

High-altitude life is rife with lore. Let’s bust some myths about CMS:

• Myth: “Drink more water and you’ll never get CMS.”
  Reality: Hydration helps overall health but doesn’t stop hypoxia-driven RBC overproduction.
• Myth: “Only trekkers get altitude sickness, not locals.”
  Reality: Locals can get CMS over years; it’s precisely a chronic adaptation failure.
• Myth: “Natural herbs are sufficient treatment.”
  Reality: No validated herbal cure. Some plants (like maca root) are touted but lack robust clinical backing.
• Myth: “You can’t do anything until you descend.”
  Reality: Phlebotomy, oxygen, and meds can manage symptoms even if descent isn’t immediately possible.
• Myth: “Acute altitude sickness and CMS are the same.”
  Reality: They share hypoxia but differ in timeline, pathophysiology, and management.

Media sometimes sensationalizes “superhuman mountain men,” ignoring that chronic hypoxia eventually takes its toll. Real-life evidence shows balanced interventions work best.

Conclusion

Chronic mountain sickness is a complex, under-recognized form of high-altitude illness affecting long-term residents above ~2,500 meters. It stems from an overzealous adaptation—too many red blood cells and persistent hypoxia—leading to headaches, breathlessness, fatigue, pulmonary hypertension, and potential heart strain. Early detection via regular check-ups, hemoglobin monitoring, pulse oximetry, and prompt management with phlebotomy, oxygen, and lifestyle changes can greatly improve quality of life. While descent remains the most definitive solution, practical measures in situ are crucial. If you suspect CMS, seek professional medical advice—timely evaluation and evidence-based treatment can make a world of difference.

Frequently Asked Questions (FAQ)

• Q1: What is chronic mountain sickness?
  A1: A condition in long-term high-altitude residents marked by excessive red blood cells and low blood oxygen, causing fatigue and headaches.
• Q2: How common is CMS?
  A2: Prevalence varies by region—up to 15–20% in Andean highlanders, lower in Tibetan populations.
• Q3: What causes it?
  A3: Chronic hypoxia triggers overproduction of erythropoietin, leading to polycythemia and hyperviscosity.
• Q4: Who is at risk?
  A4: Residents at altitudes >2,500 m, especially middle-aged men with genetic predisposition and poor living conditions.
• Q5: How is CMS diagnosed?
  A5: Based on clinical symptoms, CBC to check hemoglobin, pulse oximetry, arterial blood gases, and heart/lung imaging.
• Q6: What are key symptoms?
  A6: Frequent headaches, breathlessness with mild exertion, dizziness, ruddy complexion, sleep problems.
• Q7: Can it be treated without descending?
  A7: Yes—phlebotomy, oxygen therapy, medications like acetazolamide, and lifestyle adjustments help manage symptoms.
• Q8: Is CMS preventable?
  A8: Partly—gradual ascent, reducing indoor smoke, regular health screening, and avoiding smoking can lower risk.
• Q9: What complications can occur?
  A9: Pulmonary hypertension, right-heart failure, increased clot risk, subtle cognitive decline if untreated.
• Q10: Which doctor should I see?
  A10: Start with a primary care or local clinic; referrals often go to pulmonologists, cardiologists, or hematologists.
• Q11: Can telemedicine help?
  A11: It’s useful for initial guidance on test results and lifestyle advice but not a substitute for in-person emergency care.
• Q12: Are there myths about CMS?
  A12: Yes—herbal cures or overhydration myths persist; evidence-based treatments remain phlebotomy and oxygen.
• Q13: How soon do symptoms improve after treatment?
  A13: Some see relief within days of phlebotomy or oxygen; full adjustment may take weeks.
• Q14: Can children get CMS?
  A14: Rarely, but prolonged hypoxia in adolescent high-altitude dwellers can lead to early signs—monitor growth and symptoms.
• Q15: Does CMS lead to permanent damage?
  A15: If detected early and managed, long-term damage is limited; prolonged untreated cases risk heart and vessel complications.