Infantile Kawasaki Disease Mimicking Polyarteritis Nodosa With Severe Ischemic Complications: A Case Report.

Kawasaki disease (KD) is an acute medium-vessel vasculitis that primarily affects young children. In infants, the clinical presentation is frequently atypical or incomplete, with signs appearing progressively and non-simultaneously, which may lead to delayed diagnosis and increase the risk of severe vascular complications. Rarely, KD may present with angiographic findings mimicking polyarteritis nodosa (PAN), further complicating the diagnostic assessment. We report the case of a four-month-old male infant admitted for prolonged fever associated with initially incomplete mucocutaneous manifestations and rapidly progressive digital ischemia. The staggered appearance of symptoms resulted in initial management for presumed infection and subsequent diagnostic delay. Imaging studies revealed multiple extracoronary aneurysms involving medium-sized arteries, distal arterial occlusions, and giant coronary artery aneurysms, suggesting a systemic vasculitis resembling PAN. However, upon careful reassessment of the clinical evolution, the patient's young age and the presence of coronary artery involvement supported the diagnosis of a severe form of infantile KD. Treatment with intravenous immunoglobulins, corticosteroids, and antithrombotic therapy led to clinical and biological improvement, with regression of vascular lesions on follow-up imaging. This case highlights the importance of early consideration of KD in febrile infants presenting with systemic vascular involvement to prevent irreversible ischemic complications.