Histopathological characteristics of myocarditis in acute-phase Kawasaki disease.

AIMS: To elucidate the histopathological characteristics of myocarditis in acute-phase Kawasaki disease (KD).

METHODS AND RESULTS: The examined materials were from 29 autopsied KD patients who died within 40 disease days following onset. Each heart was divided into three levels: base, middle and apex. At each of these levels, the myocardium was divided further into the epicardial, middle and endocardial layers, and the time-courses of the changes in the myocarditis and the distribution of inflammation were analysed. Inflammatory cell infiltration, consisting mainly of lobulated leucocytes and large mononuclear cells, was seen in the myocardial interstitium in all cases. Inflammatory cell infiltration was already seen by disease day 6 in a patient with no coronary arteritis; it became prominent after day 10 and gradually disappeared after day 20. Myocarditis was initially distributed diffusely throughout the heart, but after day 10 it was localized in the base and epicardial layer.

CONCLUSIONS: In KD, myocarditis develops even earlier than epicardial coronary arteritis; it peaks by disease day 10 and then disappears gradually after day 20. The myocarditis is distributed unevenly, ranging from the entire heart to the epicardial layer of the base of the heart.