LAUSR

Resident in Internal Medicine, Mayo Clinic School of Graduate Medical Education, Rochester, MN (D.S.C., S.I.T.); Advisor to residents and Consultant in Rheumatology, Mayo Clinic, Rochester, MN (U.T.). A 46-year-old man originally from Vietnam with no known long-term medical conditions presented to a primary care clinic for evaluation of gradually progressive, left-sided, lower back pain accompanied by resolving flulike symptoms. He had a history of episodic back pain dating to his mid-20s, but the cause had never been determined. Unlike his prior episodes, on this occasion he first noticed the discomfort after what he thought was a flulike illness, characterized by fevers, chills, myalgia, malaise, and headache, as well as a 6.8-kg unintended weight loss. Although his constitutional symptoms had largely resolved in the week before his presentation, his lower back pain continued to worsen and began radiating to the perineum. His pain increased when he lay flat and was partially alleviated when he walked. The pain was generally worst at night and was accompanied by morning stiffness. He reported no focal weakness, bowel or bladder dysfunction, saddle anesthesia, or history of uveitis, psoriasis, inflammatory bowel disease, or sexually transmitted infections. On physical examination, he was afebrile, and other vital signs were within normal limits. He had marked tenderness to palpation of the left sacroiliac (SI) joint. Results of a FABER (flexion, abduction, external rotation) test were positive on the left side, and a straight leg raise yielded negative results bilaterally. There were no cutaneous lesions, enthesitis, or ocular findings. His neurologic, cardiopulmonary, abdominal, and geniturinary tract examination findings were also unremarkable. Despite a trial of nonsteroidal anti-inflammatory drugs, the patient’s pain persisted for the next several weeks, and follow-up was arranged. At that time, his symptoms and physical examination findings were largely unchanged. Laboratory studies revealed the following (reference ranges given parenthetically): white blood cell count, 7.3 10/L (3.5-10.5 10/L); erythrocyte