Bilateral Brucellar Sacroiliitis Mimicking Tuberculous or Inflammatory Spondyloarthropathy: A Case Report.

Brucellosis is a zoonotic infection, endemic in rural areas. It is caused by Brucella species, which are transmitted through the intake of unpasteurized dairy products and contact with infected animals. Sacroiliac joint involvement is common in brucellosis and typically presents as unilateral sacroiliitis. Contrarily, bilateral sacroiliitis is less typical and may mimic tuberculosis, pyogenic infection, or inflammatory spondyloarthropathy. We report a case of a 19-year-old man who presented with a one-month history of bilateral buttock pain radiating to the legs and a 2-week history of fever, chills, rigors, and febrile diaphoresis. He reported unpasteurized milk intake. Physical examination revealed bilateral sacroiliac joint tenderness, and Patrick's and Gaenslen's provocation tests elicited pain in both sacroiliac joints. Laboratory findings showed leukocytosis, elevated CRP, and ESR. Standard agglutination testing was positive for anti-Brucella antibodies, and MRI confirmed bilateral sacroiliitis, along with erosive changes and marrow edema. A diagnosis of brucellosis complicated by bilateral sacroiliitis was proposed. The patient was started on doxycycline, co-trimoxazole, and gentamicin. Gentamicin was used for 22 days, while doxycycline and co-trimoxazole were continued for a total planned duration of 13 weeks. During follow-up visits (day 15 and day 45), the patient demonstrated clinical improvement, evident by laboratory parameters, pain improvement, no fever, difficulty walking, and medication-related adverse effects. This case emphasizes that clinicians in endemic areas must consider brucellosis as a differential diagnosis in patients with bilateral lower back or buttock pain. MRI findings and serology testing are useful in early recognition. While blood cultures, PCR, and biopsy are necessary for definitive diagnosis.