Rollon-Mayordomo, AngelAvellaneda-Camarena, AnaGutierrez-Domingo, AlvaroMartinez-Carapeto, ElenaInfante-Cossio, Pedro2023-02-092023-02-0920212227-684Xhttp://hdl.handle.net/10668/18203Immunoglobulin G4-related disease (IgG4-RD) is a rare chronic systemic inflammatory pathology that poses a diagnostic challenge since it can simulate malignancy when it affects a salivary gland as a mass-like lesion. Here, the authors report an unusual clinical case of a 42-year-old man who presented with a painless, slow-growing swelling located in the right parotid gland with a 12-month evolution. Based on imaging tests and open biopsy, a diagnosis of chronic parotitis was presumed and oral methylprednisolone was prescribed. Due to poor response to medication, a total parotidectomy preserving the facial nerve was performed. The final pathology described a unilateral IgG4-related sialadenitis (IgG4-RS) in the parotid gland in combination with a poorly differentiated multifocal ductal carcinoma. The postoperative course was uneventful except for a temporary facial paresis (grade III according to the House-Brackmann classification system) that resolved completely within 5 months. There were no systemic manifestations on the whole-body 18F-FDG PET/CT. Adjuvant radiotherapy was administered without complications. Twenty-four months follow-up after surgery showed no recurrence or evidence of systemic involvement. This clinical report highlights the importance of considering the synchronous occurrence of a carcinoma underlying an isolated parotid gland mass in the context of IgG4-RS, especially if there is no response to prior steroid medication.enAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/IgG4-related sialadenitis (IgG4-RS)Immunoglobulin G4-related disease (IgG4-RD)case reporthead and neckparotid glandsalivary duct carcinomaresearch article34268092open access10.21037/gs-21-90PMC8258885https://gs.amegroups.com/article/viewFile/70634/pdfhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC8258885/pdf