Pseudohyperkalemia in myotonic dystrophy type 1: A case report

Myotonic dystrophy type 1 (DM1) is an autosomal dominant familial muscular dystrophy caused by abnormal CTG repeat expansion in the myotonic dystrophy protein kinase (DMPK) gene. The cardinal features of DM1 patients are muscular weakness, myotonia, and arrhythmia. DM1 patients with electrolyte imbalance caused by endocrinological alterations have also been reported. Herein, we report a female patient with DM1 and hyperkalemia, which fluctuated depending on the blood collection methods. We revealed that cold stimulation of red blood cells was associated with hyperkalemia, whereas blood examination immediately after collection showed normal potassium levels. She was, therefore, diagnosed with pseudohyperkalemia. Several previous reports have described DM1 patients with pseudohyperkalemia, similar to ours. Neurologists should be aware that some patients with DM1 may have pseudohyperkalemia. Thus, consider retesting with prompt measurement after blood collection to rule out pseudohyperkalemia when a patient shows hyperkalemia. If confirmed, evaluate for DM1 as a potential differential diagnosis.