Asymptomatic elevation of creatine kinase in patients with hyponatremia

Elevated creatine kinase (hyper-CKemia) has been observed in small number of patients with hyponatremia. This study evaluated the features and outcomes of patients admitted with hyponatremia complicated by hyper-CKemia. Patients admitted with hyponatremia and concurrently found to have elevated creatine kinase (CK) of above 375 IU/L (male) or 225 IU/L (female), over a 5-year period were retrospectively reviewed. Those with myocardial injury (elevated CK-MB isoenzyme [CK-MB/CK percentage of >2.5%] or Troponin T [>0.02 μg/L]), traumatic or ischemic muscle damage, primary myopathic disorder, seizures prior to CK measurement or those taking medications which can cause myopathy, were excluded. Thirty-two patients with hyponatremia and hyper-CKemia were identified. All patients had no muscular symptoms or weakness. The commonest cause of hyponatremia in this cohort was related to diuretics (50%). The mean sodium level on presentation was 116.0 ± 6.9 mmol/L and the median peak CK was 895.5 (interquartile range: 610.8-1691.8) IU/L. Six (18%) patients developed acute kidney injury (AKI). The length of hospital admission of the entire cohort was 8.0 ± 5.8 days. Patients with hyper-CKemia in the setting of diuretic-associated hyponatremia were older and had longer hospital length of stay compared with primary-polydipsia-associated. Asymptomatic hyper-CKemia is an uncommon association with hyponatremia of various etiologies. Hyponatremia-associated hyper-CKemia can be complicated by AKI.