Septic sacroiliitis due to Proteus mirabilis.

This case demonstrates the difficulty frequently encountered in making an early diagnosis of septic sacroiliitis. The proper use of appropriate laboratory tests and radiologic examinations can narrow the differential diagnosis significantly, with confirmation resting on culture results. Appropriate antibiotic therapy will depend on the organism isolated. When confronted by the typical clinical findings and supporting ancillary data of septic sacroiliitis, the physician should consider the possibility of an unusual organism such as Proteus mirabilis and should direct antibiotic therapy accordingly.