Review Question - QID 108434

A 56-year-old female presents for initial evaluation by a rheumatologist with a chief complaint of back and joint pain. She says that she has been having mild pain for years, but that the pain has become worse over the course of the last 6 months. She clarifies that the pain is most severe in the mornings just after waking up but seems to improve throughout the day. She also notices that her mouth feels dry and she has difficulty eating dry food such as crackers. Finally, she has the sensation of having bits of sand in her eyes. She denies any past medical history or medication use. Serology for which of the following would most likely be positive in this patient?