Clinical impact of persistent hyperCKemia in a Norwegian general population: A case-control study

A case control study of the relationship between persistent serum creatine kinase elevation and polyneuropathy

Creatine kinase (CK) has been associated with neuropathy, but the mechanisms are uncertain. We hypothesized that peripheral nerve function is impaired in subjects with persistent CK elevation (hyperCKemia) compared to age- and sex matched controls in a general population. The participants were recruited from the population based Tromsø study in Norway. Neuropathy impairment score (NIS), nerve conduction studies (NCS) and electromyography (EMG) in subjects with persistent hyperCKemia (n = 113; 51 men, 62 women) and controls (n = 128; 61 men, 67 women) were performed. The hyperCKemia group had higher NIS score than the controls (p = 0.050). NCS of the tibial nerve showed decreased compound motor action potential amplitude (p < 0.001), decreased motor conduction velocity (p < 0.001) and increased F-wave latency (p = 0.044). Also, reduced sensory amplitudes of the median, ulnar, and sural nerves were found. EMG showed significantly increased average motor unit potential amplitude in all examined muscles. CK correlated positively with glycated hemoglobin and non-fasting glucose in the hyperCKemia group, although not when controlled for covariates. The length dependent polyneuropathy demonstrated in the hyperCKemia group is unexplained, but CK leakage and involvement of glucose metabolism are speculated on.

Approach to the Patient With HyperCKemia

PURPOSE OF REVIEW

Neurologists commonly receive consultation requests regarding the evaluation of patients with an elevated serum creatine kinase (CK), a condition known as hyperCKemia. This article outlines an approach to the history and examination of patients with hyperCKemia in order to narrow the localization and differential of an elevated CK and guide possible next steps. This article aims to help clinicians identify treatable or reversible etiologies as well as those that will change management.

RECENT FINDINGS

An unrevealing patient history (assessing for acquired and hereditary etiologies) in an otherwise neurologically intact individual who has a normal nerve conduction study and EMG predicts that the likelihood of diagnosing the patient after further investigations will be quite low. After a comprehensive workup, a positive diagnosis is made in approximately 25% of cases of hyperCKemia.

SUMMARY

The best predictors for added diagnostic yield with further testing in hyperCKemia are a higher level of CK and a younger age; the presence of weakness increases the likelihood of a specific cause other than idiopathic or familial hyperCKemia. Many etiologies do not yet have treatments that alter clinical outcomes, and, even in the absence of a specific diagnosis, good communication with patients and primary care providers remains essential to ensure longitudinal surveillance with expectant management for potential consequences. Many patients with hyperCKemia of uncertain etiology, however, will not develop significant muscle disease on longitudinal follow-up.

Creatine kinase as a marker of obesity in a multi-ethnic population

OBJECTIVE

Creatine kinase (CK), the central regulatory enzyme of energy metabolism, is particularly high in type II skeletal muscle fibers, which are associated with insulin resistance and obesity. As resting plasma CK is mainly derived from skeletal muscle, we assessed whether plasma CK is associated with markers of obesity.

METHODS

In this cross-sectional study, we analyzed a random sample of the multi-ethnic population of Amsterdam, the Netherlands, consisting of 1444 subjects aged 34-60 years. The primary outcome was the independent association between plasma CK after rest and waist circumference. Other outcomes included waist-to-hip ratio and body mass index.

RESULTS

Mean waist circumference increased from the first through the third CK tertile, respectively 90.3 (SD 13.4), 93.2 (SD 14.3), and 94.4 (SD 13.3) cm (p < 0.001 for differences between tertiles). The increase in waist circumference was 8.91 (95% CI 5.35 to 12.47) cm per log CK increase after adjustment for age, sex, African ethnicity, educational level, physical activity and plasma creatinine. Similarly, CK was independently associated with waist-to-hip ratio and body mass index, with an increase of respectively 0.05 (95% CI 0.03 to 0.07) and 3.6 (95% CI 2.3 to 5.0) kg/m² per log CK increase.

CONCLUSIONS

Plasma CK is independently associated with measures of obesity in a multi-ethnic population. This is in line with the central role of type II skeletal muscle fibers in energy metabolism and obesity. Prospective studies should assess whether resting plasma CK could be an easy accessible marker of CK rich type II fiber predominance that helps identify individuals at risk for obesity.