IgG4 orbital inflammation in a 5-year-old child presenting as an orbital mass.

IgG4 is a newly known systemic disorder. It can present as orbital inflammation or as an orbital mass. We describe the case of a 5-year-old child with proptosis and globe dystopia who went on to have an orbital biopsy. Initially this was reported to be idiopathic orbital inflammation. After IgG4-RD was considered in the differential, the orbital biopsy was revisited, immunohistochemistry was done and the patient's serum was tested for IgG subclass levels. IgG4-RD was diagnosed and the patient was subsequently treated with prednisone and mycophenolate and made a good recovery. This is the youngest reported case of IgG4-RD in a child.