Atypical abdominal pain: uncovering malignant peritoneal mesothelioma in suspected Crohn's disease: a case report.

Background: Malignant peritoneal mesothelioma (MPM) is a rare and aggressive cancer from the serosal membranes of the abdominal cavity. In the United States, MPM accounts for about 10-15% of all mesothelioma cases, and translates into approximately 600 new cases diagnosed annually. It is typically diagnosed in Caucasian individuals, and while asbestos exposure is a well-established risk factor for pleural mesothelioma, its association with peritoneal mesothelioma remains less clear. Clinical symptoms of MPM, such as abdominal pain, bloating, and weight loss, overlap with other gastrointestinal disorders, which often leads to delayed diagnosis. This case report presents a unique instance of MPM initially misdiagnosed as ileal Crohn's disease (CD), highlighting the importance of differential diagnosis in such complex cases. Case Description: A 62-year-old Caucasian male with a history of diverticulitis was referred to an inflammatory bowel disease (IBD) center for reported ileal CD. The patient experienced 3 years of persistent abdominal pain, constipation, fatigue, early satiety, and weight loss. Previous imaging, including computed tomography scans, suggested ileal thickening and inflammatory fat stranding, but no histologic confirmation of CD was obtained. He had been treated with Humira without improvement, and intermittent courses of prednisone provided temporary relief. Despite his diagnosis of CD, his symptoms were unresponsive to standard treatments. Upon further evaluation, Humira levels were undetectable, and magnetic resonance enterography (MRE) yielded no significant findings. A diagnostic laparoscopy was performed, revealing peritoneal mesothelioma, which was confirmed by biopsy as the diffuse, epithelioid type. The diagnosis was supported by positive immunohistochemical staining for calretinin, CK7, and CK5/6. Conclusions: This case underscores the importance of considering a broad differential diagnosis in patients with non-specific abdominal symptoms. Although CD was initially suspected, MPM was ultimately identified through diagnostic laparoscopy and histological analysis. The case highlights the need for comprehensive diagnostic evaluation, including histologic confirmation and objective markers, to accurately differentiate between conditions with similar presentations. Clinicians should maintain a high index of suspicion for rare etiologies, such as peritoneal mesothelioma, particularly in patients with a history of asbestos exposure, to ensure timely and appropriate management.