S5115 Unraveling the Mystery of Persistent Eosinophilia: A Challenging Diagnosis of a Parasitic Infection

Introduction: Peripheral eosinophilia can be attributed to various etiologies, including allergic, hematologic, autoimmune, and infectious causes. However, initial inconclusive evaluations can make achieving a diagnosis cumbersome and challenging. We present a case of persistent eosinophilia and concurrent gastrointestinal symptoms ultimately caused by Strongyloides steracolis (SS) infection, despite numerous negative laboratory, serum and colon biopsies. This case underscores the importance of maintaining parasitic infection on the differential and pursuing repeat tissue sampling when clinical suspicion remains high. Case Description/Methods: A 34-year-old woman presented for evaluation of intermittent symptoms of left lower quadrant abdominal pain, abdominal bloating, and altered bowel movements for 2 months. Past medical history was significant for persistent eosinophilia (10-20%) and fibromyalgia associated with sacroiliitis. She underwent an extensive hematologic evaluation for persistent eosinophilia including serological testing and bone marrow biopsy. Extensive stool studies were inconclusive. Initial colonoscopy in January 2021 revealed diffuse granularity of the colonic mucosa with biopsy revealing moderate to severe eosinophilic infiltration (5-10%). Eosinophilic infiltration was prominent in lamina propria with associated crypt distortion; there was no evidence of granulomas, parasites, or viral cytopathic effect. Stool studies were negative for infectious etiologies including ova and parasites. In May 2022, repeat Esophagogastroduodenoscopy and colonoscopy were performed for persistent eosinophilia and continued abdominal symptoms, revealing lymphocytic gastritis and granular mucosa in proximal ascending colon and cecum. Repeat random colon biopsies revealed SS in the background of eosinophilic colitis. Ivermectin therapy was started, resulting in resolution of abdominal symptoms and eosinophilia. The patient remains in clinical remission over the last 3 years of follow up. She also had no upper gastrointestinal symptoms due to lymphocytic gastritis after eradication therapy of SS infection. Discussion: This case highlights the challenging aspect of diagnostic work up of peripheral eosinophilia due to gastrointestinal parasitic infection that was not detected on multiple stool studies and index colonoscopy. Moreover, it emphasizes the importance of repeat colon biopsies, if clinical suspicion for parasitic infection remains high.