Gastrointestinal: Abdominal actinomycosis: A disease mimicking Crohn's disease

A 68‐year‐old female farmer has suffered persistent moderate dull pain in the right lower abdomen for 19 months, without any other suggestive symptoms and signs. Laboratory data and imaging did not show evidence of infectious, autoimmune, or neoplastic diseases. Colonoscopy showed a normal terminal ileum but scattered erythematous mucosa and purulent secretions in the ileocecum (Fig. 1a). Biopsy revealed chronic inflammation with granulomas (Fig. 1b). Immunohistochemical staining of EBV‐encoded RNA, acid‐fast staining, and polymerase chain reaction test for tuberculosis were negative. Crohn’s disease (CD) was considered, and mesalazine was given for 10 months. However, her symptom was not improved, but an egg‐sized mass appeared at her right lumbar region. Abdominal computed tomography and intestinal contrast ultrasonography suspected the presence of ileocecal fistula with sinus formation extending to lumbar abdominal wall subcutaneously (Fig. 1c,d). Percutaneous puncture of the lumbar sinus was performed, but culture of the extracted pus was negative. Cefotaxime, ceftezole, and amoxicillin sulbactam were applied with standard dose for 7 days consecutively as empirical treatment, which turned out ineffective. Repeated colonoscopy showed nodular lesions in the ileocecum, and the biopsy revealed chronic inflammation. Crohn’s disease diagnosis for this patient was doubtful due to her old age of onset with striking intestinal fistula but mild symptoms, atypical findings of colonoscopy. Then ileocecal resection was indicated for ileocecal fistula with sinus formation. Surgery found that congestive and swelled ileocecum adhered closely to posterior and lateral abdominal wall. There was a fistula from ileocecum to lumbar back skin, with 1.5 cm in width and 5 cm in depth. Postoperative pathology revealed the presence of flaky mycelioid structures and granulomas (Fig. 2a). Methenamine silver staining confirmed the presence of actinomycetes (Fig. 2b). After surgery, combined with intravenous therapy of benzylpenicillin sodium (5.6 million IU × q6h for 30 days), the patient recovered completely. Her lumbar sinus was also healed. During 1‐year follow‐up, there were no signs of recurrence. The diagnosis of actinomycosis was finally confirmed. Actinomycosis, as an opportunistic infection, often affected patients with immunodeficiency, cancer, trauma, or malnutrition. However, it has also been reported in some healthy individuals. Abdominal actinomycosis is an unusual form of visceral involvement and has been reported rarely. As a group of anaerobic Gram‐positive bacteria normally colonizing the gastrointestinal tract, actinomycetes may be pathogenic when mucosal injury occurs. Appendix, cecum, and colon are the most commonly affected sites in the digestive tract. It is usually difficult to diagnose actinomycosis because of the lower positive rate of actinomycetes with routine cultivation method. Methenamine silver staining of tissue section by which typical characteristics of actinomycetes can be detected may be helpful to the suspected cases. Moreover, actinomycete infection is characterized by significant fibrosis, formation of granulomas, and transmural and suppurative inflammation with abscess and fistula, which may mimic CD. However, CD is always presented in young patients with typical findings of colonoscopy. In rare cases, actinomycete infection may also be a comorbidity in patients with CD, making the disease more complicated. In conclusion, abdominal actinomycosis may mimic fistulizing CD, and it should be considered in the differential diagnosis of CD.