1 Introduction
IgG4-related disease (IgG4-RD) is a condition in which the immune system causes inflammation and the formation of masses in various organs, including the pancreas and bile duct[1]. Nonetheless, encountering IgG4-RD involving the digestive system (identified as IgG4-related gastrointestinal disease; IgG4-GID) is rare. To date, a mere 19 instances of IgG4-GID manifesting as an isolated mass in the stomach have been recorded in medical studies. This article details the experience of a 44-year-old Asian male who received a diagnosis of IgG4-GID that appeared as an solitary gastric mass. The patient underwent surgery and showed no signs of recurrence six months post-operation.

2 Case history / examination

A 44-year-old Asian man was admitted to the hospital with chest tightness, abdominal distension, and belching. The C13 breath test yielded positive results, and a follow-up examination after 2 weeks of quadruple anti-Helicobacter pylori treatment showed negative results. Gastroscopy revealed a gastric mass(Figure 1).Endoscopic Ultrasonography(EUS) identified a hypoechoic submucosal mass measuring 2.3x1.6cm in the gastric body, originating from the fourth layer, with insufficient blood flow signal(Figure 2). Enhanced gastric Computer scan confirmed the presence of the mass tumor growing both inside and outside the gastric body,and other organs weren’t be involved. Gastric stromal tumor was firstly considered as diagnosis and ectopic pancreas or gastric lipoma was considered in the differential diagnosis.The patient underwent endoscopic submucosal dissection (ESD), which revealed that the tumor was adherent, unencapsulated, highly vascularized, and difficult to remove so converted to laparoscopic surgery. Pathological examination of the resected tissue showed submucosal nodular lesions primarily located in the gastric submucosa and muscularis. The lesions exhibited infiltration of IgG4-positive plasma cells (up to 80/HPF, Figure 3) and more than 40% of IgG4+/IgG+ plasma cells (Figure 4). Additionally, regional proliferation of vascular endothelium and inflammatory cell infiltration of nerves was observed (Figure 5).These pathological evidences pointed to IgG4-RD.
Other laboratory test results showed an elevated creatinine level of 107umol/L(normal is less than 97umol/l). However, the blood routine, coagulation function, liver function, serum IgG4 level, tumor markers, high-sensitivity C-reactive protein level, antinuclear antibodies, antineutrophils Cytoplasmic antibodies, and immunoglobulin G,immunoglobulin M and immunoglobulin A were all within normal ranges.Additional laboratory test results indicated a raised creatinine concentration, registering at 107umol/L(normal is less than 97umol/L). Yet, other tests encompassing serum IgG4 were all within acceptable limits. The food-intolerance IgG4 test showed that the serum IgG4 level of eggs was higher than 1000 U/ml.