Case report: The masquerading spectrum: a pediatric case series of IgG4-related disease.

IgG4-related disease (IgG4-RD) is a rare fibro-inflammatory condition with scarce data on its clinical spectrum and management in the pediatric population.We present a single-center observational study of six children with clinically and morphologically confirmed IgG4-RD. We analyzed the age of onset, time to diagnosis, and comprehensive clinical, imaging, laboratory, and histopathological findings at presentation and during follow-up (range: 3 months to 7 years). The 2020 revised comprehensive diagnostic criteria for IgG4-RD were used. The diagnosis was based on a biopsy of orbital tissue with detection of signs of fibrosis, obliterating phlebitis, and subsequent immunohistochemical testing for the presence of IgG4. The disease manifested itself in 4 patients with orbital pseudotumor, in 1 patient with diabetes insipidus, in 1 patient with fever, signs of high inflammatory and immunological activity. The diagnostic delay ranged from 3 to 12 months. Treatment regimens included glucocorticoids combined with cytostatic agents (n=3), cytostatic monotherapy (n=2), and initial glucocorticoid monotherapy (n=1). Three patients achieved a good clinical and radiological response without disease progression. One patient experienced multiple relapses while on topical steroid therapy, which were successfully controlled after switching to systemic cytostatic therapy. Two children achieved incomplete remission. They were advised to continue rituximab therapy. This case series underscores the diagnostic challenge and phenotypic diversity of pediatric IgG4-RD. The most common clinical manifestation in our patients was orbital involvement. Prednisone and cytostatic agents were effective for inducing and maintaining remission. Our findings contribute to the evolving understanding of this rare condition in childhood.