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

Introduction

Malignant peritoneal mesothelioma (MPM) is a rare malignancy confined to the abdominal cavity (1). In the United States, MPM accounts for about 10–15% of all mesothelioma cases, and this translates into approximately 600 new cases diagnosed annually (2). Most cases occur in Caucasians. Industrial pollutants including asbestos exposure is a well-known cause in pleural mesothelioma but less associated with peritoneal mesothelioma (3,4). Symptoms are variable and non-specific but predominantly include abdominal pain, abdominal distention, bloating, weight loss and early satiety. Due to non-specific clinical symptoms, diagnosis of MPM can be often delayed (5,6). We present a case report of reported ileal Crohn’s disease (CD) with an unexpected diagnosis of peritoneal mesothelioma. This case highlights the need for histologic confirmation of CD and thorough evaluation for other potential etiologies in complex cases. We present this case in accordance with the CARE reporting checklist (available at https://jgo.amegroups.com/article/view/10.21037/jgo-2025-272/rc).

Case presentation

A 62-year-old Caucasian male with a history of diverticulitis was referred to an academic inflammatory bowel disease (IBD) center for reported ileal CD on Humira (adalimumab) 40 mg every 2 weeks. The patient had constant stabbing abdominal pain for 3 years associated with constipation. He had fatigue and early satiety resulting in significant weight loss. He had no history of tobacco use. His mother had colon cancer, but otherwise, there was no family history of malignancy. Although he had reported asbestos exposure for approximately 40 years working as a radio technician, he had no evidence of bilateral pleural plaques or fibrosis. He was diagnosed with ileal CD at an outside hospital based on video capsule endoscopy (VCE) significant for scattered erosions in the ileum. Prior esophagogastroduodenoscopy (EGD) and colonoscopies were unrevealing. He had multiple computed tomography (CT) imaging studies with ileal thickening and moderate inflammatory fat stranding (Figure 1). He did not have iron or B12 deficiency. Fecal calprotectin was not performed. He did not have histologic confirmation of CD. He was given multiple intermittent courses of prednisone by his primary care provider or during emergency room visits. His symptoms of abdominal pain resolved immediately with prednisone. Given his clinical presentation, erosions seen on VCE, ileal inflammation and thickening findings on imaging and improvement on prednisone, he was empirically started on Humira as insurance denied Stelara and Skyrizi. His clinical symptoms did not improve while on Humira.

Figure 1 CT abdomen/pelvis with contrast showing a recurring inflammatory process. Similar changes were seen previously. (A) Coronal view involving predominately the distal small bowel (left arrow) and concomitant inflammatory changes seen in the sigmoid colon (right arrow). (B) Axial view showing dilated loops of small bowel consistent with an ileus (arrows) but no bowel obstruction seen. CT, computed tomography.

On evaluation at University Medical Center New Orleans, Humira level was checked and was undetectable with moderate antibodies. Humira was discontinued. Magnetic resonance enterography (MRE) was performed which was largely unrevealing. Due to concern for possible other etiologies such as mesenteric adenitis or panniculitis to explain his symptoms, decision was made to perform a diagnostic laparoscopy. Diagnostic laparoscopy revealed peritoneal mesothelioma, confirmed by biopsy as diffuse, epithelioid type (Figure 2). The diagnosis was supported by positive staining for calretinin, pan-keratin, cytokeratin (CK)7, and CK5/6. Other malignancies were ruled out with negative carcinoembryonic antigen (CEA), MOC-31, CK20, CDX2, desmin, SOX-10, CD45, and S100. Negative results for gene fusions in NTRK1/2/3, ALK and RET (7,8). A summary of staining/markers indicative of MPM and a visual timeline of the patient’s clinical course are provided (Tables 1,2).

Figure 2 Diagnostic laparoscopy revealed extensive tumor burden. (A) Diffuse peritoneal seeding was present. (B) Intra-abdominal tumors with peritoneal nodularity were identified, and peritoneal biopsies were performed.

CT chest revealed no evidence of thoracic metastatic disease. Staging workup at that time revealed no evidence of extra-peritoneal disease. Repeat diagnostic laparoscopy a week later to evaluate for cytoreductive surgery revealed diffuse intraperitoneal disease with majority of small bowel and small bowel mesentery involved with cancer. The patient was deemed a nonsurgical candidate and referred to MD Anderson for opinion regarding further management. Repeat CT imaging one month later showed increasing peritoneal carcinomatosis (Figure 3). The patient was recommended palliative systemic chemo-immunotherapy on protocol 2022-0982 (phase 2 randomized trial of neoadjuvant or palliative chemotherapy with or without immunotherapy for peritoneal mesothelioma) and was randomized to Arm 1 with carboplatin + pemetrexed + bevacizumab + atezolizumab (9).

Figure 3 CT abdomen/pelvis with contrast showed the patient’s known peritoneal mesothelioma—matted peritoneal, omental and mesenteric disease predominantly in the right lower quadrant (left arrow) but seen throughout the abdomen (right arrow). There is nodular thickening associated with the fissure of the ligamentum teres measuring 3.4 cm loculated thin wall fluid collection in the pelvis measuring 9.6 cm × 7.4 cm. Small volume ascites is also seen in the pelvis. No bowel obstruction or hydronephrosis. CT, computed tomography.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent for publication of this case report and accompanying images was not obtained from the patient or the relatives after all possible attempts were made.

Discussion

This case highlights the critical importance of maintaining a broad differential diagnosis when evaluating non-specific abdominal symptoms. While CD was initially suspected due to bowel wall thickening seen on imaging and erosions on VCE, the patient never had a confirmed diagnosis of CD as histology was not obtained via enteroscopy. The scattered ileal erosions may represent a normal variant, nonsteroidal anti-inflammatory drug (NSAID)-induced enteropathy, or ischemia, though the latter typically presents in a segmental distribution. It is suspected that the patient had a spontaneous mesothelioma since pathogenic germline variants were not found. Despite patient reported asbestos exposure, he did not have long-term effects noted in his lungs.

The patient’s prompt symptomatic improvement with prednisone may be due to the potent anti-inflammatory and immunosuppressive effects of corticosteroids, which transiently suppress both tumor-associated and paraneoplastic inflammatory responses. Peritoneal mesothelioma often induces a robust inflammatory environment in the peritoneum, leading to symptoms such as abdominal pain and ascites with elevated systemic inflammatory markers. Glucocorticoids can reduce cytokine production (notably IL-6), vascular permeability, and leukocyte infiltration, thereby alleviating these symptoms even in the absence of true autoimmune or granulomatous disease. It is also important to recognize that granulomatous or sarcoid-like reactions can occur in the vicinity of tumors, including mesothelioma, and these inflammatory changes are steroid-responsive, potentially mimicking primary granulomatous diseases (e.g., CD, tuberculosis, or histoplasmosis). This can further confound the clinical picture and lead to a misleading but rapid clinical response to steroids. However, this response is typically transient, and symptoms often recur or progress as the underlying malignancy advances (10,11).

In patients with persistent symptoms and radiographic abnormalities, pursuing diagnostic laparoscopy is essential. It remains the only definitive method to directly inspect the parietal peritoneum and the serosal surfaces of the bowel, which are inaccessible to endoscopic biopsy and may harbor pathology not evident on mucosal sampling. Laparoscopy with biopsy is the gold standard for diagnosing MPM, as imaging and cytology lack specificity and fine-needle or endoscopic biopsies may not provide adequate tissue or access to the relevant surfaces (7,12).

Historically, MPM carried a poor prognosis. The median overall survival ranges from 6 to 12 months without treatment. However early diagnosis, individualized treatment plans based on specific disease characteristics and specialized treatment centers have improved outcomes (4,13,14). With cytoreductive surgery and hyperthermic intraperitoneal chemotherapy this combination has significantly improved survival rates. Median overall survival can extend from 34 to 92 months, with 5-year survival rates between 39% and 91%, depending on factors like tumor burden and histological subtype (5,15). For patient’s ineligible for surgery, chemotherapy regimens such as pemetrexed combined with cisplatin have shown median overall survival of approximately 13.1 months (6,14).

As an educational tool for gastroenterology and oncology providers, this case challenges reliance on clinical impressions, encourages diagnostic laparoscopic biopsy and further workups for atypical presentations to avoid missed or delayed diagnoses of rare but serious conditions. On the other hand, it is limited in generalizability as a single case report. This case also illustrates the impact of cognitive heuristics, such as anchoring and premature closure, where overreliance on an initial diagnosis (e.g., CD) despite persistent unexplained findings and poor response to therapy can hinder timely consideration of alternative diagnoses such as MPM.

Conclusions

This case report highlights a rare, atypical presentation of peritoneal mesothelioma in setting of asbestos exposure in a patient thought to have ileal CD, illustrating the complexities in diagnosing peritoneal mesothelioma. This case underscores the need for vigilant monitoring using clinical evaluation, objective markers with labs, imaging, endoscopy and histopathology to accurately diagnose diseases, assess disease activity and guide treatment. It is imperative to consider other etiologies particularly in the setting of non-specific symptoms to ensure appropriate diagnosis and treatment plan.

Acknowledgments

The abstract has previously been published in the Advances in Inflammatory Bowel Diseases (AIBD) Abstract Book.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://jgo.amegroups.com/article/view/10.21037/jgo-2025-272/rc

Peer Review File: Available at https://jgo.amegroups.com/article/view/10.21037/jgo-2025-272/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jgo.amegroups.com/article/view/10.21037/jgo-2025-272/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent for publication of this case report and accompanying images was not obtained from the patient or the relatives after all possible attempts were made.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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