Beyond the Cloudy Effluent: Unveiling Hidden Adenocarcinoma in a Patient on Peritoneal Dialysis with Suspected Peritonitis

Introduction: Several case reports have documented instances where peritoneal dialysis patients presenting with symptoms suggestive of PD-related peritonitis were ultimately diagnosed with peritoneal malignancies due to metastatic disease. Case Description: 78-year-old Female with DM2, HTN, Gout, history of cervical cancer s/p TAH-BSO and brachytherapy 25 years ago, history of breast cancer s/p lumpectomy, radiation, and endocrine therapy 8 years ago with ESKD on automated peritoneal dialysis presented with abdominal pain for two weeks. She was diagnosed with culture negative peritonitis recently twice by her dialysis unit, latest episode was 2 weeks ago for which she recieved intraperitoneal vancomycin and oral fluconazole. Despite completion of the therapy, she remained symptomatic and presented to our hospital. PD fluid sent for cell count, grams stain, culture, and cytology showed RBC count 1086/cumm , WBC count 6356/cumm, segmented neutrophils 45%, lymphocytes 9%, monocytes/histocytes 43%, gram stain and culture were negative and cytology showed malignent cells consistent with adenocarcinoma with following immunohistochemical results (BerEp4+, CK7+, CK20+, CDX2+). Diffenential for sites of origin based on the biomarkers included GI, pancreatobiliary, or ovarian. Mammogram was normal. Total body CT scan showed abnormal thickening of the cecum and proximal ascending colon conceraning for colon cancer. Colon cancer markers were elevated :CA19-9 (1166 U/ml), and CEA (22 ng/ml). Patient refused further workup including colonoscopy and went home on hospice. Discussion: This case highlights the diagnostic complexity in a PD patient presenting initially with presumed peritonitis, but ultimately found to have metastatic adenocarcinoma. It is important to consider the refractory and recurring nature of the peritontis in a PD patient and broaden the differential for etiology to more than bacterial peritonitis. Detailed look of the peritoneal fluid analysis of the cell differential demonstrated only 45% neurophils and 43% monocyte/histocyte predominance. This is atypical for bacterial infection, which usually is over 50% neurtophil count and low monocyte count. Next step in evaluation is to send the effluent for cytology and consider imaging which done in this case established the diagnosis.