A 24-yeаr-оld wоmаn presents tо her doctor complаining of abdominal pain and diarrhea. For the past 6 months she has noticed loose stools associated with diffuse abdominal pain. The diarrhea is non-bloody and not associated with any particular foods. She has had intermittent fevers during the past month and reports a 7 lb. unintentional weight loss, but denies any recent travel. She has a history of anxiety and nephrolithiasis. She is currently taking paroxetine and a combined oral contraceptive. Her temperature is 100.1°F (37.8°C), blood pressure is 110/60 mmHg, pulse is 75/min, and respirations are 14/min. Physical exam reveals a thin young woman with normal heart and lungs sounds. Her abdomen is diffusely tender to light palpation with increased bowel sounds. Multiple shallow ulcers are found on the oral mucosa, and a perianal tag is noted during rectal exam. What is most likely to be found on additional workup for this patient?