Erythema nodosum in children: a cohort study from a tertiary pediatric hospital in Italy.

Erythema nodosum (EN), although relatively uncommon in the pediatric population, is the most frequent type of panniculitis in children. The present study aimed to report all the cases of children admitted to our tertiary pediatric hospital with the diagnosis of EN to evaluate the epidemiology, clinical manifestations, etiology, treatment, and the course of this disease in the pediatric age. This observational study retrospectively considered all children evaluated to the emergency room (ER) of Meyer Children's University Hospital, Florence, Italy, discharged with a diagnosis of EN over a 12-year period (from January 2009 to December 2021). Clinical and laboratory data were recorded using a standardized report form. Sixty-eight patients with EN were included. The etiologic diagnosis of EN was made in 38 children (55.9%): 29 (42.6%) had infection-related EN (in particular EBV and β-hemolytic streptococcus), 6 (8.8%) had Crohn's disease, 1 celiac disease, 1 Sjogren syndrome, and 1 Hodgkin lymphoma. In 30 patients (45%), no definitive diagnosis was reached, and they were defined as having idiopathic EN. Most of the laboratory tests were nonspecific. No statistical differences were found in the demographic and clinical data, and the main diagnostic laboratory parameters between patients with idiopathic EN versus those with secondary EN.  Conclusion: Since EN can be isolated or the first manifestation of heterogeneous underlying pathologies, some of which can be severe and life-threatening, it is important to recognize it and carry out all the necessary etiological diagnostic investigations to understand its etiology and start the specific treatment. What is Known: • Erythema nodosum (EN) is the most frequent type of panniculitis in children. • It has been associated with a wide spectrum of disorders, such as different types of infection, malignancies, chronic inflammations, and drugs. What is New: • No statistical differences can be found in clinical features as well as laboratory data, between patients with idiopathic EN versus those with secondary EN. • A broad spectrum of investigations and a proper follow-up should be taken into account in order to prevent a delayed or missed secondary EN diagnosis.