Mesenteric panniculitis (MP) is a rare idiopathic condition characterised histologically by chronic inflammatory and fibrosis of mesenteric adipose tissue (1-2). Ogden et al (3) introduced the term MP to encompass sclerosing mesenteritis and mesenteric lipodystrophy. While these conditions share the same features, they differ in the relative predominance of chronic inflammation or fibrosis Pathological features predominant in inflammation are termed MP, whereas those predominant in fibrosis are termed sclerosing mesenteritis (1-2). A systematic review showed that MP primarily affects middle-aged men, presenting most commonly with abdominal pain (78.1%), followed by fever (26.0%), weight loss (22.9%), diarrhoea (19.3%) and vomiting (18.2%) (1). Abdominal tenderness (38.0%) and masses (34.4%) are observed on physical examination (1). MP diagnosis is difficult due to the presentation of non-specific symptoms and unclear findings. Chylous ascites has been reported in two case series of patients with MP, demonstrating frequencies of 18.5% (minimal chylous ascites) (3) and 14.1% (no information regarding amount of ascites) (4). To the best of our knowledge, few case reports describe massive chylous ascites (5-7). Similarly, chylous pleural effusion, a rare complication in patients with MP, has only been documented in two reports, to the best of our knowledge (8-9).

Protein-losing enteropathy (PLE) is characterised by uncompensated loss of plasma protein in the intestines, leading to panhypoproteinemia in the absence of liver or kidney dysfunction (10,11). Studies have identified mucosal damage and lymph drainage failure as primary mechanisms underlying PLE, with several factors contributing to the development of these mechanisms, including inflammatory conditions (such as Crohn's disease and ulcerative colitis), cardiovascular disorders (such as chronic congestive heart failure) and widespread abdominal malignant neoplasms (such as malignant lymphoma and multiple myeloma) (10-11). To the best of our knowledge, however, only six cases of MP-associated PLE have been published (12-17).

The present study reported a case of MP complicated by massive chylous ascites, pleural effusion and PLE and reviewed clinicopathological characteristics of these conditions.

To the best of our knowledge, the present study is the first to report MP accompanied by massive chylous ascites, pleural effusion and PLE. Although a premortem diagnosis of MP was not made, histopathological examination during autopsy revealed findings that were consistent with MP. Excessive fluid buildup and protein loss were likely attributed to intestinal lymph drainage obstruction caused by mesenteric inflammation, fibrosis and fat necrosis in MP.

MP is an idiopathic condition characterised by chronic inflammation and fibrosis of mesenteric adipose tissue (1-2). MP is associated with infection, autoimmune disease and abdominal trauma (1). Certain cases of MP result from IgG4-associated diseases (19). although most cases showed no such associations (20). Therefore, the absence of IgG4-positive plasma cells in the present cased ruled out differential diagnoses for IgG4-related diseases. Since MP is predominant in middle-aged male patients presenting with non-specific symptoms, such as abdominal pain, fever, weight loss and diarrhoea (1), its diagnosis is often difficult. Previous studies have reported a postmortem diagnosis of MP, similar to the present case (9,14). Imaging studies may be valuable diagnostic tools in visualizing certain MP features. CT demonstrates hyperattenuating fat with tumoural pseudocapsules and soft tissue nodules in the mesentery (1,4,21). Magnetic resonance imaging demonstrates an ill-defined, hyperintense signal in mesenteric fat on T2-weighted imaging, reflecting early-stage oedema, followed by a hypointense signal in later stages (1). Calcification, which is a potential consequence of fat necrosis, may be observed in the mesentery (4,7,14), as in the present case. Notably, the presence of calcification might be a characteristic finding on CT scans for MP. Furthermore, while small intestinal mesentery is the most commonly affected site (1), lesions in both the small intestine and colon are possible, as in the present case. The treatment strategy for MP typically involves administration of steroids, colchicine, tamoxifen and antibiotics, with over 70% of patients showing symptom resolution (1,4,21). However, non-responders have been documented (1,4,14,15), with some developing fatal outcomes on follow-up (1,9,14). Here, the patient succumbed to respiratory failure despite medical treatment.

Massive chylous pleural effusion and PLE were rare features in the present case. Table I summarises clinicopathological characteristics of MP cases with chylous pleural effusion or PLE, including the present case (8,9,12-17). To the best of our knowledge, only two prior cases of MP with massive pleural effusion have been documented (8,9). Kobayashi et al (9) reported an autopsy-confirmed case of MP with relatively minimal chylous ascites (200 ml) and massive pleural effusion (left, 1,300; right, 1,400 ml). Although the mechanism underlying chylous effusion in bilateral thoracic cavities remains unclear, transfer from the abdomen via a diaphragmatic defect is hypothesized (8,9). Similarly, bilateral pleural effusion may be present in patients with hepatic hydrothorax and diaphragmatic defect (22,23). In the present case, massive chylous ascites and pleural effusion were observed. While no macroscopic diaphragmatic defect was observed during autopsy, negative intrathoracic pressure may have facilitated transfer of chylous fluid from the abdomen to the pleural cavity. Additionally, autopsy revealed shrunken lungs covered with dense, white fibrous tissue. This feature resembles ‘trapped lung’, which is a consequence of dysfunctional healing following pleural injury (24). This condition progresses from lung entrapment to formation of a visceral pleural peel, persistent pleural effusion and inability of the lung to expand (24). These changes are marked by fibrosis and scarring of visceral pleura, resulting in a peel-like appearance and trapped lung (24). While infection is the most common cause, pneumothorax, haemothorax, thoracic intervention and rheumatoid pleuritis can also lead to trapped lungs (24). Moreover, Owen et al (25) reported complications of trapped lungs and chylothorax in a patient with long-standing cirrhosis due to hepatitis C. Considering the aforementioned findings, the persistent massive chylous pleural effusion in the present case may have contributed to the development of trapped lungs.

Despite its rare occurrence, PLE can be a symptom of MP (Table I). Chylous ascites have been noted in four of seven patients with MP and PLE including the present patient (13,14,17). Among MP patients with PLE, only one showed symptom improvement with steroid therapy (12). In the present case, the patient initially showed improvement of oedema, although worsening ascites and pleural effusion were observed. The occurrence of PLE in MP is likely due to lymphangiectasia of the small intestinal mucosa caused by lymph drainage obstruction (14). Autopsy findings in the present case suggested MP as the underlying cause of PLE. Although rare, PLE may be recognised as a possible complication of MP. Examination including imaging studies and histological examination of the affected mesentery are therefore warranted for diagnosis of MP.

To the best of our knowledge, the present study is the first to describe MP with massive ascites, pleural effusion and PLE, highlighting the potential of MP changes in obstructing lymph drainage in the mesentery. Despite its rarity and non-specific symptoms, MP should be included as a differential diagnosis in patients presenting with the aforementioned features.