Episodic hyponatremia in mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS).

Various organ involvements and endocrinologic abnormalities associated with electrolyte imbalance, including hyponatremia, are seen in patients with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS); however, the clinical significance of hyponatremia in these patients is rarely reported. We analyzed the serum sodium concentration profiles and clinical and laboratory data of seven patients with MELAS. We found that hyponatremia occurred episodically in four of the seven patients from an early stage of the disease. We identified excessive sodium loss in urine to be associated with the hyponatremic episodes and the causes of hyponatremia in two patients as relative adrenal insufficiency, acute renal failure, and serious paralytic ileus. However, even extensive examinations failed to reveal the cause in other patients. Because severe hyponatremia can cause serious complications, clinicians should pay attention to serum sodium levels and maintain them properly in patients with MELAS.