Review Question - QID 216439

A 22-year-old woman presents to her primary care physician with severe rectal pain and painful bowel movements. She states that defecating has become so painful that she now avoids it, and her last bowel movement was 5 days ago. Sometimes, she notices a small amount of blood on the toilet paper. These symptoms have progressively worsened over the past month. The patient smokes 1-2 cigarettes a week for the past year and has 2 male sexual partners. Her temperature is 99.2°F (37.3°C), blood pressure is 120/85 mmHg, pulse is 72/min, respirations are 16/min, and oxygen saturation is 100% on room air. Physical exam reveals a small linear skin tear in the posterior midline right next to the anus. Which of the following is the most likely diagnosis?