A Unique Adverse Event of Radiotherapy in a Patient With IgG4-related Disease: A Case Report.

BACKGROUND/AIM: IgG4-related disease (IgG4RD) is a rare autoimmune proinflammatory condition that mimics other cancers and has unique pathological findings. The effects of radiotherapy in patients with IgG4RD remain unknown. CASE REPORT: A male patient in his seventies who received radiotherapy (68 Gy/39 fr) for bladder cancer 5 months prior, presented to our hospital with fatigue and swelling in both legs. The patient had a history of IgG4-related sclerosing cholangitis, a subtype of IgG4RD. Leg edema gradually worsened despite treatment with a diuretic agent. Computed tomography showed hyperdense soft-tissue lesions in the irradiated area. The serum level of IgG4 increased to 1,380 mg/dl. One month after administration of a corticosteroid (10 mg per day) as an ex juvantibus treatment for IgG4RD, leg edema disappeared. Soft-tissue lesions in the irradiated area decreased in size. The adverse event was ultimately diagnosed as the recurrence of IgG4RD in the irradiated area. To the best of our knowledge, this is the first case report of an adverse event of radiotherapy for a patient with IgG4RD. CONCLUSION: We experienced a unique adverse event of radiotherapy in a patient with IgG4RD. Caution is advised on radiotherapy administration in patients with IgG4RD.