A case of multisystem inflammatory syndrome in children in a Japanese boy: with discussion of cytokine profile.

The new disease concept of multisystem inflammatory syndrome in children (MIS-C), which is a systemic inflammatory syndrome with multiple organ involvement after SARS-CoV2 infection, was established in 2020. MIS-C is common in Hispanic and black children in Europe and North America, with few reports in East Asians. A significant portion of patients with MIS-C develop Kawasaki disease (KD)-like symptoms. Therefore, differential diagnosis is challenging, especially in East Asia, where KD is most prevalent. No Japanese cases have been reported in the literatures so far. We report a case of MIS-C in Japan with KD-like symptoms. A 9-year-old Japanese boy, who was infected with SARS-CoV2 1 month previously along with his family, was admitted to our hospital owing to fever for 6 d and erythema mainly in the groyne and pubic area. He also had conjunctivitis, strawberry tongue and diarrhoea. His laboratory findings were as follows: WBC, 12,840/µL (lymphocytes, 4%); CRP, 22.6 mg/dL, pro-calcitonin, 1.8 ng/mL (normal, <0.50 ng/mL); NT pro-BNP, 7627 pg/mL (<125 pg/mL); and troponin T, 0.14 ng/mL (<0.01 ng/mL). His cardiac function was normal. We initially diagnosed him with KD. His fever rapidly resolved with intravenous immunoglobulin (IVIG) and there were no coronary artery lesions. Desquamation of the fingers was observed later. Finally, a history of SARS-COV2 infection, his age, atypical skin rash, elevation of markers of inflammation and heart failure and lymphopenia suggested the diagnosis of MIS-C rather than KD. Differentiation between KD and MIS-C is necessary even in Japan, especially in patients with atypical features of KD.