Granulomatous vasculitis is a necrotizing small-vessel vasculitis, and granulomatous inflammation is strongly associated with anti-neutrophil cytoplasmic autoantibodies . The typical clinical manifestation is a triple syndrome, that is, upper respiratory disease, pulmonary inflammation and glomerulonephritis. Gastrointestinal tract involvement is uncommon, and is usually found at autopsy. The types of lesions mainly include submucosal edema, ulcers, hemorrhage, mesenteric ischemia, intestinal obstruction and perforation. The diagnosis of gastrointestinal complications depends largely on these clinical manifestations.
Pagnoux et al.  conducted a study on 62 patients with systemic necrotizing vasculitis that involved the gastrointestinal tract, and found that the most common symptoms were abdominal pain (97%), nausea, vomiting, diarrhea, bloody stools, and melena. Furthermore, previous studies have also observed these symptoms [10, 11]. The locations of GPA lesions in the gastrointestinal tract are diverse, and can involve all parts of the intestine. The most common pathological manifestations are ulcer, intestinal necrosis and perforation [2, 3, 10, 11].
Although the present understanding of gastrointestinal lesions in GPA patients has increased, there are few reports on the endoscopic appearance of GPA involving the bowel with accompanying images. In previous years, Robin et al.  reported a case of GPA with intestinal lesions mainly characterized by ulcers. However, the tissue biopsy was nonspecific inflammation, and lacked the characteristics of granulomatous vasculitis. Endoscopic biopsy findings are often non-specific inflammation, ulcers, or erosions, and these can rarely be diagnosed as GPA. Camilleri et al.  pointed out that this may be correlated to superficial tissue biopsy, because the small and medium blood vessels are located deeper under the mucosa. Therefore, it is also necessary to distinguish between infectious bowel diseases, non-infectious inflammatory bowel diseases and ischemic colitis, such as Crohn’s disease characterized by aphthous ulcers, paving stone-like changes, and segmental lesions and ischemic enteritis characterized by longitudinal map-like ulcers. Besides, side effects of immunosuppressants should also be excluded. In the present case of GPA, the colonoscopy has revealed a manifestation of black ring-shaped lesion not previously reported in any disease. The degenerative intestine mucosal tissue formed a black ring-shaped membranous tissue that could be traversed by an endoscope. The intestinal wall biopsies beneath it had characteristics of inflammatory granulation, with no normal colon glands. This has not been observed in previous studies. However, colonoscopy was not performed after treatment with immunosuppressants and glucocorticoids.
In conclusion, when GPA patients suffer from abdominal pain, diarrhea, bloody stools, or melena, the differential diagnosis should be made while taking into account the possibility of granulomatous vasculitis involving the gastrointestinal tract. Colonoscopy combined with tissue biopsy can help to determine the nature of the disease, and provide an effective method for differential diagnosis.