Hypoxic ventilatory depression in a patient with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes.

We describe a case of a 21-year-old man with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) who presented with hypoxic ventilatory depression. He had chronic hypoventilation, which was not explained by weakness of respiratory muscles. His hypercapnic ventilatory response was not impaired. In contrast, hypoxic ventilatory depression was observed in the isocapnic progressive hypoxic response test. After exposure to hypoxic conditions, his respiratory frequency decreased and tidal volume was unchanged. The hypoxic ventilatory depression was partially blocked by pretreatment with aminophylline. In conclusion, we need to be careful with patients with MELAS who are hypoxaemic because a vicious circle of hypoxia and hypoventilation can occur.