Recurrent incomplete Kawasaki disease with small-joint-predominant arthritis during the acute phase

An adolescent boy was admitted on illness day 6 with fever and left cervical lymphadenopathy. He had been treated for complete Kawasaki disease (KD) approximately a decade earlier. He subsequently developed painful swelling of the left wrist and bilateral finger and toe interphalangeal joints, impairing grip strength; ultrasonography confirmed synovitis. Although fever resolved by illness day 12, arthritis persisted. New conjunctival injection, lip erythema and a secondary rise in C-reactive protein led to a diagnosis of incomplete KD on illness day 18, followed by intravenous immunoglobulin. Arthritis rapidly improved and he was discharged without residual joint symptoms or coronary artery abnormalities. KD-associated arthritis may vary by disease phase, with acute-phase polyarthritis sometimes involving small joints and later arthritis affecting larger joints. Distinguishing this presentation from systemic juvenile idiopathic arthritis can be challenging; serial reassessment of the clinical course and treatment response is essential.