What Is Altitude Sickness?

Altitude sickness, also called acute mountain sickness, is a collection of symptoms that can develop when a person ascends to high elevations too quickly and the body has not had time to acclimatise to the reduced oxygen and lower air pressure. Altitude sickness can be mild, moderate, or severe. Its most common form involves fatigue, headache, poor appetite, and dizziness, but severe cases can progress to life-threatening fluid accumulation in the brain or lungs.

Why Does Dizziness Occur at High Altitude?

Dizziness is one of the hallmark symptoms of altitude sickness. Several factors contribute to its development. The reduced partial pressure of oxygen at altitude causes hypoxia, or low oxygen delivery to tissues, including brain tissue. The inner ear, which contains the vestibular system, is particularly sensitive to changes in blood oxygen and pressure. In addition, alterations in breathing patterns, such as periodic breathing during sleep, can change carbon dioxide levels and affect the acid-base balance of the blood, which in turn can affect the function of the vestibular nerve and central balance pathways.

Dizziness in altitude sickness is often reported as a feeling of lightheadedness, unsteadiness, or a sensation of movement when there is none, known as vertigo. The symptoms may worsen with physical exertion and are frequently accompanied by headache, nausea, and a lack of coordination.

The Role of Otoneurology

Otoneurology is the medical specialty that focuses on the evaluation and management of disorders affecting the inner ear, the vestibular system, and the neural pathways that connect balance and hearing with the brain. Otoneurology considers dizziness, vertigo, imbalance, and hearing-related problems together, because these symptoms often share a common origin in the peripheral or central vestibular system.

In the context of altitude sickness, otoneurology provides a valuable framework for understanding why dizziness happens and how it can be distinguished from other causes of dizziness, such as benign paroxysmal positional vertigo, vestibular migraine, or Ménière disease. While atmospheric pressure changes, hypoxia, and physical exertion all interact in a high-altitude environment, the otoneurological evaluation helps to map symptoms to specific structures, such as the semicircular canals, the otolith organs, or the vestibular nuclei in the brainstem.

Types and Stages of Altitude Sickness

Altitude sickness is generally classified into several overlapping conditions:

• Acute mountain sickness (AMS): The mildest and most common form, with symptoms such as headache, dizziness, fatigue, shortness of breath, and sleep disturbance.
• High-altitude cerebral edema (HACE): A severe and potentially fatal form of altitude sickness in which the brain swells due to fluid leakage. Dizziness progresses to confusion, hallucinations, clumsiness, and altered consciousness.
• High-altitude pulmonary edema (HAPE): A severe fluid accumulation in the lungs that can accompany or follow AMS. HAPE causes severe breathlessness, cough, and weakness, reducing oxygen delivery to the brain and worsening dizziness.

The risk of altitude sickness rises with increasing elevation, particularly above 2,500 metres, and is greater when a person ascends rapidly without adequate rest. Individual susceptibility varies and a prior history of altitude sickness is a strong predictor.

How Dizziness Is Assessed in Altitude Sickness

A careful history and targeted physical examination are essential to evaluate dizziness at altitude. Key questions involve the timing and triggers of dizziness, whether it occurs with movement or at rest, whether it is accompanied by hearing loss, tinnitus, or ear fullness, and whether there is a sense of spinning versus lightheadedness. A neurological and otoneurological examination may include tests of eye movement, positional testing, balance and gait assessment, and observation for nystagmus, which is an involuntary rhythmic movement of the eyes that can accompany vestibular disorders.

At altitude, a simple clinical evaluation can often distinguish benign lightheadedness due to hypoxia from more serious neurological signs such as ataxia, which is a severe sign of cerebral oedema. Ataxia, or inability to coordinate movements, is a key warning sign that deterioration is occurring and that immediate descent is required.

Prevention and Management

The most effective way to prevent altitude sickness is a gradual ascent that allows acclimatisation. A common recommendation is that once above 3,000 metres, an individual should not increase sleeping altitude by more than about 500 metres per day and should include a rest day every two or three days. Adequate hydration, a light diet, and avoidance of alcohol and sedatives are also helpful.

If symptoms of altitude sickness, particularly headache and dizziness, develop, the primary treatment is descent to a lower altitude. Further ascent should be stopped until symptoms resolve. Supplemental oxygen and medications such as acetazolamide can be helpful in preventing and treating mild symptoms, but they should never be used as a substitute for descent in severe cases.

For individuals who are prone to dizziness or who have pre-existing balance disorders, an otoneurological assessment before travel to high altitude can provide useful guidance. Working with a knowledgeable physician can help identify risk factors and set realistic plans for gradual ascent, monitoring of symptoms, and emergency response.

Key Takeaways

Altitude sickness is a common and potentially dangerous condition that affects travellers, mountaineers, skiers, and workers who travel to high elevations. Dizziness is a prominent symptom, and it can arise from hypoxia, changes in breathing, and the effects of reduced pressure on the vestibular system. Otoneurology offers a specialised way of evaluating dizziness and balance, providing important insight into how altitude affects the inner ear and its connections in the brain.

Anyone who develops dizziness at altitude should respect the symptom as a sign that the body is struggling to adapt. Rapid or worsening dizziness, especially when accompanied by headache, vomiting, confusion, or unsteadiness, requires immediate descent and urgent medical attention.