Serum sickness-like reaction in pediatric age - experience of an Imunoalergology Unit

Background: Serum sickness is a systemic reaction reported after administration of heterologous serum. It is clinically characterized by fever, skin lesions, arthralgia/arthritis, lymphadenopathy, and nephritis and by presence of immune complexes. Serum sickness-like reaction mimics serum sickness and its pathophysiology is not well understood. It is more common in pediatric age and often associated with drug administration. This study aimed to characterize serum sickness-like reaction cases evaluated at a Drug Allergy Clinic. Material and methods: An analytical, retrospective, longitudinal study of a sample of 39 children (56% male) with diagnosis of serum sickness-like reaction evaluated at a Drug Allergy Clinic between January 2007 and December 2017 was performed. Results: Children had an average of 4.8 years at the time of reaction. In most cases (97%), beta-lactam antibiotics were the suspected triggering drugs. On average, clinical manifestations developed 7.5 days after treatment start. Skin lesions developed in all patients, and arthralgia/arthritis in 92.3%. Fifteen percent of children were hospitalized. Penicillin-specific IgE was evaluated in 87% of patients, but only tested positive in two. Skin prick tests and intradermal tests were performed in 46% of cases and were positive in seven. Oral challenge test was performed in 26% of patients and was positive in three. Conclusion: Serum sickness-like reaction is a rare and poorly understood entity. Diagnosis is essentially clinical, requiring a high index of suspicion. In the acute phase, usefulness of complementary tests lies mainly in the differential diagnosis with other diseases.