Serum macromolecular creatine kinase type 1 as a diagnostic clue in inflammatory bowel disease?

In adults, macromolecular creatine kinase (CK) type 1 has been linked to ulcerative colitis (UC), but not to Crohn's disease (CD). We present two patients with pediatric inflammatory bowel disease (IBD) in which macrocreatine kinase (macro-CK) type 1 led to the final diagnosis of UC. A 13 year old with bloody diarrhea and weight loss was diagnosed with CD. CK elevation was interpreted as perimyocarditis attributed to CD. CK elevation persisted; however, cardiac evaluation remained unremarkable. CK gel electrophoresis revealed macro-CK type 1. During a disease flare-up and reevaluation (endoscopy and histology), the diagnosis was changed to UC. A 12-year-old girl with bloody diarrhea, weight loss, and anemia was diagnosed with CD (patchy distal colitis and aphtoid lesions). Repeated CK elevation was observed. Gel electrophoresis confirmed macro-CK type 1. After reevaluation during a flare-up (endoscopy and histology), the diagnosis was changed to UC. Conclusion CK elevation in pediatric IBD could suggest macro-CK type 1 formation, which is possibly linked to UC. In a subset of IBD patients, macro-CK type 1 could help differentiate UC from CD.