The challenge of diagnosing psoas abscess.

Diagnosing psoas abscess in patients with low back pain might be hampered by their atypical symptoms. We describe a case in which a 39-year-old retired provost marshal presented to our emergency facility with acute onset of low back pain following an episode of lumbar strain during a flight. His initial computed tomography of lumbar spine and abdominal sonography were inconclusive. Two weeks later, he was admitted to our rehabilitation unit for similar symptoms. One day later, leukocytosis and elevated c-reactive protein following rising body temperature were found. Fever of unknown origin (FUO) was impressed after series of laboratory studies. However, an inflammatory gallium scan performed 2 weeks later due to persistent fever revealed active infection in the L4 vertebra and soft tissue of the L5 paraspinal region. MRI was then performed and demonstrated abnormal enhancement at the bodies of the L2 and L3 vertebrae, prevertebral soft tissue and bilateral psoas muscles. A CT-guided percutaneous aspiration of 10 cc yellowish pus was attained, which yielded no pathogens. His symptoms subsided 1 week after being given appropriate antibiotics. This case showed the importance of nuclear scanning and MRI in patients with low back pain and FUO. It also suggests that repeated imaging study and/or other modality should be considered when the initial imaging result is not compatible with the clinical presentation of psoas abscess, which was initially missed by image studies.