Symptoms of mountain sickness are due to hypoxia of the brain. The pathogenesis is complex, but acid–base disturbances certainly play a role. When arterial oxygen levels drop, hyperventilation is induced, resulting in a respiratory alkalosis. However, this alkalosis inhibits the hyperventilation necessary for maintaining oxygen pressure. We present a case of a patient with symptoms of mountain sickness at relatively low altitudes, who appeared to have Conn’s syndrome (primary hyperaldosteronism). A 61-year-old male with hypokalaemic hypertension presented with symptoms of mountain sickness at relatively low altitudes. Hyperaldosteronism was suspected and laboratory results showed a non-suppressible aldosterone concentration and a mild metabolic alkalosis. A CT scan of the abdomen revealed an adenoma in the left adrenal gland. Treatment of aldosterone blockade by eplerone normalized blood pressure and the symptoms of mountain sickness at low altitudes disappeared completely. We suggest that in our patient with hyperaldosteronism, the pre-existing metabolic alkalosis inhibited the central respiratory centre after relatively mild hyperventilation. Therefore, mountain sickness in our patient could occur at a relatively low altitude.
