A 36-year-old man from California who had been skiing at a Colorado ski resort for 3 days developed cough, shortness of breath, headache, and dizziness. The patient has no previous medical problems and takes no medication. He does not use tobacco, alcohol, or illicit drugs. Temperature is 38.3 C (100.9 F), blood pressure is 110/70 mm Hg, and pulse is 102/min. Oxygen saturation is 86% on room air. Examination shows cyanosis, dry mucous membranes, normal jugular venous pressure, and bilateral lung crackles. Heart sounds are normal. There is no peripheral edema. Neurologic examination shows no focal findings. Leukocytes are 13,000/mm³ with 75% neutrophils. The patient is given antibiotics and high-flow oxygen as well as strict bed rest. Six hours later his symptoms markedly improve with a decrease in oxygen requirements. What is the most likely diagnosis?

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Explanation: 11ec25c8_d1fb_f4d1_bc81_3da4b926d180_MD0003_00 This patient with shortness of breath, headache, and dizziness within several days of arriving at high elevation (ie, >2500 m [~8000 ft]) likely has high-altitude illness. His cough, greater-than-expected hypoxemia, and bilateral lung crackles suggest high-altitude pulmonary edema (HAPE), a potential complication of high-altitude illness. hypoxemia In response to the low partial pressure of inspired oxygen (PiO₂) at high altitude, the lungs undergo hypoxic vasoconstriction to optimize alveolar-capillary gas exchange. Some individuals have a genetic predisposition to developing unevenly distributed hypoxic vasoconstriction, which exposes the pulmonary capillaries in relatively less vasoconstricted areas to high perfusion pressure. The regional elevations in perfusion pressure disrupt the alveolar-capillary membrane and lead to patchy, bilateral pulmonary edema (noncardiogenic pulmonary edema). ₂ bilateral pulmonary edema The differentiation of HAPE from bacterial pneumonia (Choice A) can be challenging as both conditions can cause fever, leukocytosis, hypoxemia, and bilateral lung crackles. Recent ascent to high altitude suggests HAPE; conversely, an extended stay at high altitude prior to symptom onset rules out HAPE as it almost never occurs after >1 week at the same altitude. Mild leukocytosis is common with HAPE, but leukocytes >15,000/mm³ or the presence of bands suggests bacterial pneumonia. Rapid improvement of hypoxemia with supplemental oxygen is highly suggestive of HAPE. Although hypoxemia due to multifocal pneumonia does not improve quickly with supplemental oxygen (due to widespread intrapulmonary shunting), supplemental oxygen alleviates the hypoxic vasoconstriction in HAPE to reduce alveolar-capillary perfusion pressure and rapidly improve the edema and hypoxemia. (Choice B) Cardiogenic pulmonary edema involves the transmission of elevated left atrial pressure back to the pulmonary veins and capillaries, most commonly due to left ventricular dysfunction (ie, decompensated heart failure). Dry mucous membranes and the absence of jugular venous distension rule out volume overload and cardiogenic pulmonary edema. (Choice D) Although tachycardia and hypoxemia are typical of acute pulmonary thromboembolism, clear lungs would also be expected, and marked improvement within hours with antibiotics and oxygen therapy but not anticoagulation would be unusual. (Choice E) Although viral pneumonia can rarely present as alveolar consolidation with bilateral lung crackles, interstitial inflammation without alveolar consolidation (or lung crackles) is more typical. Viral pneumonia can sometimes cause significant hypoxemia, but, as with bacterial pneumonia, the hypoxemia is unlikely to improve within several hours. Educational objective: High-altitude pulmonary edema (HAPE) typically presents with shortness of breath, cough, hypoxemia, and bilateral lung crackles. Characteristics that favor HAPE over multifocal pneumonia include recent ascent to high altitude, the absence of leukocytes >15,000/mm³, and rapid improvement with supplemental oxygen. ³ References: Update on high-altitude pulmonary edema: pathogenesis, prevention, and treatment. (http://www.ncbi.nlm.nih.gov/pubmed/19099331)

A 36-Year-Old Man from California Who Had Been Skiing at a Colorado