[The limitation of MB isoenzyme of creatine kinase mass in assess myocardial injury with muscular disease].

OBJECTIVE: To examine the changes in serum MB isoenzyme of creatine kinase mass (CK-MB mass), cardiac troponin I (cTnI), and myoglobulin (Mb) in children with myocarditis and muscular disease in order to evaluate the significance of index CK-MB mass for the diagnosis of myocardium injury in these diseases. METHODS: Blood samples were collected from 40 children with myocarditis, 38 children with muscular diseases, and 10 healthy children, for the measurement of creatine kinase (CK), CK-MB activity, CK-MB mass, cTnI, and Mb. Myocarditis patients also received electrocardiogram and pulse Doppler electrocardiogram examination while muscular diseases patients were subjected to electro-myographic examination, inherit-metabolic diseases screening and related gene analysis. The data were analyzed for differences between groups, and differences between values before and after the treatment. RESULTS: In comparison with healthy controls [CK (U/L): 95.0 ± 27.0, CK-MB activity (U/L): 22.6 ± 1.3, CK-MB mass (μg/L): 2.4 ± 0.3, cTnI (μg/L): 0.012 ± 0.001], the patients with myocarditis had significantly (all P < 0.01) higher mean values in CK (1033.0 ± 408.0), CK-MB activity (101.2 ± 31.5), CK-MB mass (38.2 ± 13.2) and cTnI (5.544 ± 1.554) before the treatment. After 2 weeks of treatment these indexes returned to the level of controls, with cTnI responded the last (CK: 59.3 ± 25.1, CK-MB activity: 24.6 ± 13.2, CK-MB mass: 3.3 ± 2.9, cTnI: 0.125 ± 0.128). One week after treatment, the incidences of CK and CK-MB mass elevation were significantly lower than the values before the treatment [CK: 5.9% (1/17) vs. 56.4% (22/39); CK-MB mass: 8.3% (1/12) vs. 61.1% (22/36), both P < 0.01], with the change in CK-MB mass appeared significantly earlier than cTnI [8.3% (1/12) vs. 73.7% (14/19), P < 0.05]. The patients with muscular disease also had significantly elevated mean value in CK (10193.0 ± 1447.0), CK-MB activity (311.7 ± 44.4), and CK-MB mass (229.2 ± 47.9) in comparison with healthy controls before the treatment (all P < 0.01). But their cTnI (0.021 ± 0.002) was not significantly different from the control at this time. Two weeks after treatment, the elevated indexes were still significantly higher than the control (CK: 5735.6 ± 6187.8, CK-MB activity: 170.7 ± 143.0, CK-MB mass: 207.4 ± 136.6), while the level of cTnI (0.230 ± 0.150) remained at the level of the control group. The incidence of index elevation was not significantly different from the values before the treatment for all the indexes tested [CK: 85.7% (6/7) vs. 97.4% (37/38); CK-MB activity: 85.7% (6/7) vs. 97.4% (37/38); CK-MB mass: 100.0% (2/2) vs. 94.1% (32/34); cTnI: 0(0/1) vs. 6.4% (2/31), all P > 0.05]. CONCLUSIONS: In patients with myocarditis, CK-MB mass and cTnI both follow a consistent pattern of change: elevated in the acute stage of the disease but return to normal after recovery. In patients with muscular diseases, these 2 indexes have different pattern of change. CK-MB mass is significantly higher than control even after the treatment, while cTnI value remain unchanged. Therefore, CK-MB mass has very limited value as an index for myocardial injury in these patients.