Rationale: Immunoglobulin G4-related disease (IgG4-RD) is an inflammatory condition of unknown cause. Cancer might be related to the development of certain IgG4-RD but to date, little literature documents it.
Patient concerns: A 78-year old man presented with unilateral proptosis responsive to steroids, initially attributed to nonspecific orbital inflammation.
Diagnosis: Right hemicolectomy was performed because of a suspicious lesion which turned out to be tubulovillous adenoma on histological analysis. Eight months after the surgery, a mass infiltrating the mesentery was found and biopsy revealed IgG4-RD.
Interventions: Both the orbital inflammation and abdominal mass infiltrating the mesentery were responsive to steroids and rituximab administered to treat IgG4-RD.
Outcomes: In the course of IgG4-RD, the patient developed bilateral optic perineuritis, causing bilateral visual loss. Colon cancer with synchronous multiple liver metastases was found 1 year after rituximab treatment.
Lessons: This case raises the possibility of IgG4-RD being a paraneoplastic syndrome in some patients. Cancer screening should probably be performed in some elderly patients diagnosed with IgG4-RD.