Duloxetine as a Primary Cause of Microscopic Colitis: A Case Report

Abstract

Introduction: Lymphocytic colitis is a subtype of microscopic colitis (MC), an inflammatory condition characterized by excessive watery diarrhea and endoscopically normal colonic tissue. Many etiologies, including adverse effects from medications, are thought to lead to this condition via an exaggerated immune response. This is evident by lymphocyte aggregates visible on histological specimens. Case: This is a case of a 33-year-old female who presented with a chief complaint of loose, watery diarrhea of 4 weeks duration. She reported abdominal pain with up to 10 bowel movements per day. She denied any other symptoms, including GI alarm symptoms. Her pertinent medical history included GERD and fibromyalgia, managed with duloxetine for the past 4 months. Additional medications included gabapentin and valacyclovir. Other history included no recent use of antibiotics, travel, sick contacts, or changes in diet or medication. Initial stool studies noted a negative pathogen panel and normal pancreatic elastase level. However, fecal calprotectin and lactoferrin levels were elevated, raising the index of suspicion for an inflammatory process. Other labs included normal levels of TTG IgG and IgA antibodies, ESR, CRP, Saccharomyces cerevisiae IgG and IgA antibodies, and Anti-Neutrophil Cytoplasmic Antibodies. Colonoscopy was subsequently performed which noted a normal terminal ileum, scattered mild erythematous mucosa in the sigmoid colon, and internal hemorrhoids. Random and focused biopsies were obtained in the terminal ileum and throughout the colon. Small bowel biopsies were unremarkable. Biopsies of the ascending, transverse, descending, and sigmoid colon revealed colonic mucosa with acute and chronic inflammation in the lamina propria and chronic cryptitis. These findings were consistent with active MC, lymphocytic subtype. She subsequently began to decrease her dose of duloxetine with an eventual plan to discontinue the medication altogether. Budesonide was also prescribed for 8 weeks. Within 1 week, her symptoms improved. However, it was not until she fully discontinued the duloxetine that her symptoms completely resolved. Discussion: This patient's clinical course demonstrates a likely case of duloxetine induced MC. While there have been 6 published case reports of duloxetine induced MC, it remains a rarely reported entity. When evaluating for causes of MC, one should always pay close attention to a patient's medications as the possible causative agent.