A case of chronic mountain sickness diagnosed by routine pulmonary function tests

Area of Science:

• Pulmonary Medicine
• Sleep Medicine
• Altitude Physiology

Background:

• Cor pulmonale and respiratory acidosis can present diagnostic challenges, particularly in differentiating primary cardiopulmonary disease from central ventilatory control abnormalities.
• Altitude natives often exhibit blunted responses to hypoxia and hypercapnia, with a subset showing a significantly reduced drive to breathe.

Observation:

• A patient presented with symptoms suggestive of cardiopulmonary disease, but arterial blood gases revealed a normal alveolar-arterial gradient, indicating hypoxemia due to hypoventilation.
• Pulmonary function tests showed evidence of air trapping but otherwise normal parameters, further complicating the diagnosis.
• The patient exhibited frequent and severe nocturnal desaturations with hypopnea, consistent with abnormal ventilatory control during sleep.

Findings:

• The clinical presentation and diagnostic findings supported a diagnosis of chronic mountain sickness (CMS), also known as Monge's disease.
• The diagnosis was established using routine arterial blood gases and standard pulmonary function tests, without the need for more specialized ventilatory responsiveness testing.

Implications:

• This case highlights that CMS, characterized by a profoundly depressed ventilatory drive, should be considered in altitude natives with unexplained hypoxemia and respiratory abnormalities.
• Standard, non-invasive diagnostic tools are sufficient for identifying CMS, simplifying the diagnostic pathway for clinicians.
• Understanding the central ventilatory drive abnormalities is crucial for managing hypoxemia and related complications in high-altitude populations.