immunoglobulin g4 ( igg4)-related disease ( igg4rd ) is a relatively recently defined condition that is histologically characterized by an extensive infiltration of lymphocytes and igg4-positive plasma cells with storiform fibrosis . at present , it is known that various organs can be affected by igg4rd , including the pancreas , bile duct , gallbladder , liver , lung , salivary gland , retroperitoneum , and gastrointestinal tract . , we report a case of igg4rd of the stomach presenting as a subepithelial mass without any other organ involvement . autosomal dominant polycystic kidney disease was diagnosed on abdominal computed tomography ( ct ) , and she was referred to our gastroenterology clinic for further evaluation of an intramural enhancing mass in the gastric fundus that was incidentally found on the ct scan ( fig . 1 ) . she had no gastrointestinal complaints , and physical examination showed no abnormalities . the laboratory results were unremarkable except for hypocytic and hypochromic anemia ( hemoglobin , 10.1 g / dl ) . helicobacter pylori - positive lymphofollicular gastritis was seen , and , macroscopically , a 4-cm subepithelial mass with surface ulceration was found on the fundus ( fig . endoscopic ultrasonography ( eus ) showed a 3.41.6 cm well - circumscribed homogeneous hypoechoic mass located mainly in the muscularis mucosa and submucosa ( fig . 2c ) . because multiple biopsy specimens only showed chronic ulcer on microscopic examination , laparoscopic wedge resection was performed to rule out tumors with malignant potential such as a neuroendocrine tumor ( net ) or gastrointestinal stromal tumor ( gist ) . grossly , the resected specimen showed a well - defined whitish - gray solid subepithelial mass ( fig . fibrosis admixed with inflammatory cells was seen composing the submucosal mass that extended to the subserosa ( fig . bland - looking spindle cells were arranged in a storiform pattern in the collagenous stroma ( fig . 4b ) , and there was a dense infiltration of polymorphous inflammatory cells composed predominantly of plasma cells with a few lymphocytes , eosinophils , and neutrophils ( fig . these spindle cells showed one to two mitoses per 10 high power fields ( hpfs ) , and positive staining for smooth muscle actin and negative staining for alk , desmin , cd34 , dog-1 , c - kit , and s-100 . additional immunohistochemical staining revealed increased igg - positive and igg4-positive plasma cells ( 402/hpf and 102/hpf , respectively ) , and the ratio of igg4+/igg+ plasma cells was 25.3% ( fig . because these pathological features were compatible with igg4rd , and there was no evidence of any other organ involvement , isolated gastric igg4rd was finally diagnosed . the serum igg and igg4 levels were not elevated ( 1,012 and 295 mg / l , respectively ) . she was discharged without significant postoperative complications , and there has been no evidence of disease recurrence during the 1-year follow - up period . igg4rd was first proposed as a new clinicopathological entity by kamisawa et al .   in 2003 as a multisystemic disease in patients with autoimmune pancreatitis . igg4rd is histologically defined as an intensive infiltration of igg4-positive plasma cells and t - lymphocytes with storiform fibrosis , and clinically known to respond well to steroids . multiple organs can be affected synchronously or metachronously , including the pancreas , biliary tree , liver , kidneys , salivary gland , orbit , breast , pericardium , aorta , skin , lungs , prostate , meninges , retroperitoneum , and gastrointestinal tract . recently , many cases of igg4rd affecting organs other than the pancreas have been reported , such as igg4-related inflammatory pseudotumors of the liver , lungs , and greater omentum   with or without autoimmune pancreatitis , and isolated igg4rd seems to have been increasingly detected owing to an increased awareness of this disease entity . however , igg4rd in the stomach is still rare . on the basis of the eight cases reported thus far , the gastric manifestations of this disease seem to consist of two types : polypoid mass - like ( six cases ) or ulcerative ( two cases ) lesions ( table 1 ) . rollins et al . first described 5 to 6 cm gastric igg4-related pseudotumors with no evidence of any other organ involvement as confirmed with laparoscopic resection . thereafter , na et al .   reported an 8-mm gastric nodular igg4rd confirmed with endoscopic submucosal dissection , and kim et al . described two cases of igg4-related inflammatory pseudotumors in the stomach , in which eus showed a well - defined homogeneous hypoechoic mass arising from echo layer 4 ( muscularis propria ) . on the other hand , fujita et al .   reported a case with refractory gastric ulcers that worsened after standard proton pump inhibitor therapy and h. pylori eradication , and similarly bateman et al .   described a case of intractable gastric ulcer showing storiform fibrosis and abundant infiltration of igg4-positive plasma cells . of a total of eight cases reported , only one case of ulcerative - type igg4rd was possible to confirm by using conventional endoscopic biopsy with elevated serum igg4 levels . for the remaining seven cases , the patients had to undergo surgical or endoscopic resection for the final diagnosis , and their serum igg4 levels were within the reference range . in this regard , na et al .   suggested that predominant inflammatory infiltrates of igg4rd in the gastric submucosa while sparing the mucosa seem to make the diagnosis difficult . furthermore , endoscopic and radiographic difficulties in distinguishing igg4rd from other malignancies or tumors with malignant potential are also reasons for a troublesome diagnosis . these situations lead to a higher possibility of unnecessary surgery in these patients , although igg4rd is a medically treatable condition that responds well to steroid therapy . in our case , macroscopically , a 4-cm subepithelial mass with surface ulceration was incidentally found on the fundus , and eus revealed a well - circumscribed homogeneous hypoechoic mass located mainly in the muscularis mucosa and submucosa . although endoscopic biopsy failed to detect the disease , we considered laparoscopic wedge resection to rule out a net or gist without doubt . after obtaining the final diagnosis and reviewing similar cases in which patients had undergone unnecessary surgery , we learned that clinical awareness and suspicion of igg4rd is the most important factor in diagnosing this disease entity . although h. pylori - associated gastritis was seen in our case , there has been no evidence of a link between igg4rd and h. pylori infection thus far . in conclusion , isolated gastric igg4rd is very rare . because it is difficult to endoscopically differentiate igg4rd from other potentially malignant tumors and to definitively identify the disease with conventional endoscopic biopsy , it is most important to recognize this disease entity to avoid unnecessary surgery . because igg4rd is known to respond well to steroids , it is important to attempt to confirm the disease before considering invasive surgery . furthermore , we suggest considering igg4rd in the differential diagnosis in the presence of a gastric subepithelial mass that has a homogeneous hypoechoic feature on eus .
immunoglobulin g4 ( igg4)-related disease ( igg4rd ) is a relatively recently recognized entity that is histopathologically characterized by an extensive infiltration of lymphocytes and igg4-positive plasma cells with dense fibrosis . 
 igg4rd is now known to affect any organ system , and a few cases of gastrointestinal lesions have also been reported . however , solitary igg4rd of the stomach is still very rare . 
 furthermore , as it can mimic malignant conditions , it is important to recognize this disease to avoid unnecessary surgery . 
 herein , we present a case of igg4rd presenting as an isolated subepithelial mass in the stomach .