Acute Scrotal Involvement in Kawasaki Disease: A Potential Clinical Clue to Persistent Disease Activity

Kawasaki disease (KD) is an acute vasculitis and the leading cause of acquired heart disease in children. Coronary artery aneurysms (CAAs) arise from vascular inflammation during the acute phase; however, in some patients, inflammation may persist despite treatment, and reliable clinical indicators of ongoing disease activity remain limited. Acute scrotal involvement is a rare manifestation of KD, and its clinical significance has not been well established. Here, we report a case of a previously healthy 49-month-old boy who presented with 4 days of fever and the five principal features of KD. He was initially treated with intravenous immunoglobulin, aspirin, and prednisolone, resulting in transient improvement. On Day 7 of illness, he developed recurrent fever and right inguinal pain. Fever persisted on Day 8, accompanied by recurrent lip erythema and worsening inflammation, prompting a second dose of intravenous immunoglobulin. His fever improved on Day 9, when right-sided scrotal erythema and swelling became evident. Ultrasonography revealed a right hydrocele with preserved blood flow and no epididymal torsion. Echocardiography on Day 11 demonstrated medium-sized bilateral CAAs, which were subsequently confirmed by coronary computed tomography. The scrotal findings resolved completely within 1 month. This clinical course suggests that acute scrotal involvement may represent a potential clinical clue to persistent disease activity in KD, warranting careful reassessment for evolving coronary artery involvement.