Differentials
Asthma, acute exacerbation
SIGNS / SYMPTOMS
Although the absence of common triggers such as house dust mites, pollution, and pollen may improve the symptoms of some sufferers, exercise, low humidity, and cold exposure may exacerbate the condition in others.[65]
The presence of wheeze and diurnal variation of symptoms is rare in high-altitude pulmonary edema (HAPE).
INVESTIGATIONS
Therapeutic trial with short acting beta-2 agonists should significantly improve symptoms.[25]
Community-acquired pneumonia
SIGNS / SYMPTOMS
May be difficult to clinically differentiate.
The presence of green or yellow sputum, rigors, and a high fever that do not resolve on descent are suggestive of pneumonia.
INVESTIGATIONS
Elevated WBC and positive sputum cultures.
CXR may demonstrate infiltration, consolidation, effusions, and cavitation.
Acute exacerbation of chronic heart failure (CHF)
SIGNS / SYMPTOMS
While significant numbers of individuals with cardiac risk factors head to altitude, the vast majority do not.[66] It is therefore far more likely that those presenting with peripheral edema, cyanosis, tachypnea, cough, and blood-stained sputum are suffering from HAPE and should be treated accordingly.
Pronounced right-sided heart failure (ascites, hepatomegaly, and an elevated jugular venous pressure) may help distinguish the condition from HAPE.
Presence of a gallop rhythm or a heart murmur (will be absent in HAPE).
INVESTIGATIONS
Cardiomegaly on CXR.
ECG may demonstrate arrhythmia, ischemic ST- and T-wave changes.
Echo shows abnormal systolic and diastolic function.
Hyperventilation syndrome
SIGNS / SYMPTOMS
May be triggered by the demands of the high-altitude environment; therefore is often difficult to distinguish clinically from HAPE.
Those with HAPE predominantly suffer from the effects of hypoxia; those with hyperventilation will be affected by hypocapnia, dizziness, paresthesia, and perceptual disturbances.
INVESTIGATIONS
Diagnosis is clinical.
Myocardial infarction
SIGNS / SYMPTOMS
Unlike the chest pain in HAPE, MI pain is often described as a crushing pain radiating into the neck, jaw, and arms. While this may be eased with oxygen and rest similar to HAPE, descent may have little effect upon such symptoms.
The presence of acute mountain sickness symptoms and evidence of cough and abnormalities on chest auscultation makes a diagnosis of HAPE more likely.
INVESTIGATIONS
ECG demonstrates arrhythmia or acute ischemic ST- and T-wave changes.
Cardiac catheterization will demonstrate abnormal coronary flow.
Pulmonary embolism
SIGNS / SYMPTOMS
In the absence of clinical signs of deep vein thrombosis (pain, swelling, and redness in an affected limb) distinguishing pulmonary embolism (PE) from HAPE is difficult in the field setting.
In the absence of any improvement on descent or HAPE treatment, the diagnosis of HAPE will be unlikely.
INVESTIGATIONS
Positive D-dimer.
ECG changes suggestive (but not diagnostic) of PE include tachycardia, new right axis deviation, new right bundle branch block and the classical S wave in lead I, Q wave with T-wave inversion in lead III.
Ventilation-perfusion scan demonstrates abnormality in perfusion.
CT pulmonary angiography demonstrates the presence of thrombus in the pulmonary vessels.
Acute psychosis
SIGNS / SYMPTOMS
Thought disorder, delusions, and sensory hallucinations are features consistent with a diagnosis of acute psychosis.
Although high-altitude cerebral edema (HACE) tends to present with motor symptoms, visual disturbance, and changes in the level of consciousness, in some cases the condition can be confused with psychotic behavior (personality changes and episodes of bizarre behavior).
Unlike HACE, symptoms may resolve spontaneously at altitude or persist for long periods without any evidence of physical deterioration typically seen in HACE.
In acute psychosis treatment with dexamethasone and supplemental oxygen will be ineffective.
INVESTIGATIONS
Diagnosis is clinical.
Carbon monoxide poisoning
SIGNS / SYMPTOMS
Difficult to differentiate clinically.
Carbon monoxide poisoning has been found to occur at altitude following prolonged exposure to gas stoves in confined areas such as snow holes or small tents.[67]
Typically, individuals present with flu-like symptoms before eventually developing ataxia, confusion, and loss of consciousness.
INVESTIGATIONS
Carboxyhemoglobin level is elevated.
Dehydration
SIGNS / SYMPTOMS
Warm temperatures, prolonged periods of exertion, and limited access to clean water makes dehydration a common problem at altitude. Like acute mountain sickness, headache, nausea, dizziness, and tiredness may all occur. However, these symptoms tend to respond quickly to 1 to 2 liters of isotonic fluid. In addition, thirst, orthostatic hypotension, reduced urine output, and the presence of dry skin and mucous membranes may all help distinguish dehydration from high-altitude illness.
INVESTIGATIONS
Diagnosis is clinical.
Diabetic ketoacidosis (DKA)
SIGNS / SYMPTOMS
Known history of insulin-dependent diabetes. Recent infection or change in insulin therapy.
The presence of polyuria, thirst, and acetone on the breath supports the diagnosis of DKA. May be precipitated by high altitude.[68]
INVESTIGATIONS
Elevated glucose level.
Ketonuria.
Exhaustion
SIGNS / SYMPTOMS
While exhaustion may follow a prolonged period of exertion at altitude, difficulties in sleeping, nausea, headache, and dizziness should be absent.
Importantly, in exhausted individuals abnormal neurologic signs are absent and they should still be able to perform basic tasks such as eating, drinking, and going to the toilet.
INVESTIGATIONS
Diagnosis is clinical.
Hangover
SIGNS / SYMPTOMS
Headache, nausea, and malaise of a hangover can mirror the symptoms of acute mountain sickness.
A history of excess alcohol use, an absence of sleep disturbance, and improvement with fluids and simple analgesics supports hangover as a cause of symptoms.
INVESTIGATIONS
Diagnosis is clinical.
Hypoglycemia
SIGNS / SYMPTOMS
Neurologic changes seen following prolonged periods of hypoglycemia are easily confused with illness at high altitude.
In the absence of blood glucose measurement, a history of palpitations, shakiness, and cold extremities may be associated with the early manifestations of a hypoglycemic attack.
Clinical improvement following the administration of sugary foods makes acute mountain sickness unlikely.
INVESTIGATIONS
Low glucose level.
Hyponatremia
SIGNS / SYMPTOMS
Symptoms are similar to acute mountain sickness and high-altitude cerebral edema; however, cramps and a raised body temperature (>102.2°F[>39°C]) may distinguish these from heat exhaustion and salt depletion.[69][70]
Those with heat exhaustion respond to salt replacement and appropriate fluid resuscitation.
In cases of hyponatremia caused by the intake of excessive amounts of water, fluid restriction is necessary.
INVESTIGATIONS
Electrolytes abnormal, although diagnosis is clinical in field.
Hypothermia
SIGNS / SYMPTOMS
Difficult to differentiate clinically.
Core temperature low.
Warming measures (hot water bottles, additional layers of dry clothing, and the consumption of warm drinks and food) will correct symptoms.
Hypothermia can often occur in those with HAPE or HACE.
INVESTIGATIONS
Diagnosis is clinical.
Ingestion of hallucinogenic agents
SIGNS / SYMPTOMS
A wide range of hallucinogenic agents are now available in popular high-altitude destinations.
While psychiatric symptoms predominate, changes in neurology can make it difficult to distinguish their use from HACE.
Supplemental oxygen and other HACE treatments will have no effect.
A thorough history from teammates and onlookers is essential.
INVESTIGATIONS
Diagnosis is clinical.
Migraine
SIGNS / SYMPTOMS
Ascent to high altitude is a recognized trigger for migraine.
The presence of a prodrome and aura may help distinguish migraine from acute mountain sickness (AMS). Similarly, migraine headaches tend to be unilateral and pulsating and unlike AMS can be accompanied by nasal stuffiness, scalp tenderness, and changes in bowel and bladder habits.
While migraines typically last for up to 72 hours, AMS symptoms may persist for longer and sometimes only resolve with descent.
Unlike some migraines, AMS is not associated with menstruation and does not cause visual disturbances or unilateral motor weakness.
INVESTIGATIONS
Diagnosis is clinical.
Seizures, generalized
SIGNS / SYMPTOMS
In high-altitude cerebral edema, seizures tend to occur in the final stages of the condition and will have been preceded by other symptoms.
At altitude, seizure activity in those with epilepsy varies between individuals. The combination of poor sleep, hypoxia, and hypocapnia has been postulated as a cause for increasing activity in some cases.[71]
A thorough history is useful in these cases and may identify changes in the patient's medication compliance; or, in those presenting with unexpected seizures, there may be evidence of unexplained events several years before.[71]
INVESTIGATIONS
MRI and EEG are confirmatory and will demonstrate epileptiform activity, and focal or localizing abnormality.
Stroke
SIGNS / SYMPTOMS
Most commonly present with amaurosis fugax, dysphasia, and unilateral disturbances in sensory and motor function, in some cases changes in consciousness can occur that may be clinically difficult to differentiate from HACE.
HACE is often preceded by symptoms of acute mountain sickness and improves with descent and appropriate treatment; symptoms of transient ischemic attack or stroke often persist.
INVESTIGATIONS
CT head will demonstrate ischemia or hemorrhage.
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