Microscopic colitis (MC) is a chronic inflammatory bowel disease characterized by watery diarrhea and a macroscopically normal-appearing colonic mucosa on colonoscopy. It is classified into lymphocytic colitis (LC) and collagenous colitis (CC). Its incidence has increased in developed countries, but data from Latin America remain limited. We present the case of a 65-year-old woman with fibromyalgia and recent use of duloxetine, who presented with chronic diarrhea. Colonoscopy revealed edematous mucosa with loss of vascular transparency, deep furrows with a cobblestone-like appearance, and an open dot-like surface pattern. Histopathological analysis confirmed a diagnosis of LC. After discontinuing duloxetine, the diarrhea resolved spontaneously without the need for corticosteroids. Although MC has traditionally been described as presenting with a normal-appearing colonic mucosa, studies h...