COVID-19 infection-induced worsening of recurrent CK-MB isozyme elevation due to macro-CK type 1 in a child: case report.

Background: Macro-creatine kinase (macro-CK) type 1, a macroenzyme composed of creatine kinase (CK) and immunoglobulin, is associated with hypothyroidism, tumour, autoimmune diseases, myositis, and cardiovascular diseases, and may even be found in the absence of associated pathology. However, its relationship with coronavirus disease (COVID-19) infection remains unreported.

Case Summary: An 11-year-old male patient presented with recurrent myocardial enzyme abnormalities, mainly manifested as elevated activities of CK and CK isoenzyme [particularly CK-myocardial band (MB)] with activity inverse (CK-MB higher than CK). Dynamic examinations revealed a continuous increase in CK-MB activity closely related to infection, peaking immediately after COVID-19 infection (CK 1838 U/L and CK-MB 1644 U/L). Nonetheless, the patient remained asymptomatic, with the normal results of cardiac magnetic resonance imaging and muscle biopsy and persistently normal results of echocardiogram and electrocardiogram. He had normal values of CK-MB mass and high-sensitivity troponin T (hs-cTnT) suggesting possible false elevation of CK-MB activity assayed via immunoinhibition-based CK-MB measurement. Macro-CK type 1 was confirmed by CK isoenzyme electrophoresis with a macro-CK type 1 band detected in the patient's serum. The patient remained asymptomatic over a year's follow-up.

Discussion: The sustained pseudoelevation of CK-MB activity caused by macro-CK type 1 is often misdiagnosed as myocardial damage. This diagnosis can be established via agarose gel electrophoresis of CK and CK mass assay. This case illustrates that COVID-19 infection closely correlates with macro-CK type 1 occurrence. It highlights the clinical value of understanding the relationship and emphasizes the importance of education for differential diagnosis to avoid misdiagnosing myocardial damage.