[Pseudohyperkalemia in myotonic dystrophy].

Serum electrolytes were measured in 14 patients with myotonic dystrophy and 25 healthy controls. The serum level of sodium was 144.8 +/- 3.2 (mean +/- SD) mEq/l in myotonic dystrophy and 142.0 +/- 1.9 mEq/l in the controls, and the level of potassium was 4.6 +/- 0.4 mEq/l and 4.0 +/- 0.3 mEq/l, respectively. Both electrolyte levels were significantly higher in the disease (p < 0.01, p < 0.001). Blood samples obtained from 5 patients and 5 controls were allowed to stand at room temperature, and serum electrolyte levels were repeatedly measured at 5, 30, 60, 120 minutes after blood collection. The measurement of serum potassium in myotonic dystrophy was elevated in the parallel with standing-time. The serum potassium was significantly higher in the patients than in the controls at 60 and 120 minutes standing. These results suggest that myotonic dystrophy has red blood cell membrane abnormality which allows potassium to leak.