A prospective cohort study of serum sickness-like reactions in the pediatric population

Background Serum sickness-like reaction (SSLR) is a hypersensitivity response, typically triggered by antibiotics or infections, presenting with rash, joint pain, and fever. Misdiagnosis is common due to the lack of standardized diagnostic criteria. Objective To characterize clinical and laboratory features of SSLR in pediatric patients to improve diagnostic accuracy and management. Methods A prospective cohort study was conducted at the Children's Hospital in London, Ontario, from October 2022 to September 2024. Children (0 to 18 years) presenting with rash and joint pain or edema were enrolled. Data included clinical presentation, laboratory findings, joint ultrasound results, and treatment outcomes. Results Of 27 patients, 59% were males. The mean age at the presentation was 4 years. Amoxicillin was the most frequent trigger (85.2%). Annular morphology was the most common presentation of skin rash. Ultrasound ruled out true arthritis. The rash was resolved in about 5 days and the joint pain in 4 days. Systemic steroids accelerated joint pain resolution but did not reduce disease duration. Lymphocyte toxicity assays confirmed drug causality in 58.3%, correlating with annular rash and elevated T-cell activation markers. Conclusions The findings have important implications for the diagnosis, management, and prognosis of SSLR in pediatric patients, paving the way for future research in this area.