Luke N. Ledbetter MD, Presenter: Nothing to Disclose

Karen Lisa Salzman MD, Abstract Co-Author: Consultant, Amirsys, Inc Stockholder, Amirsys, Inc

Lubdha Mahavir Shah MD, Abstract Co-Author: Nothing to Disclose

Spine infections, including vertebral body osteomyelitis and discitis, are relatively common causes of morbidity and mortality. The most common clinical symptom is nonspecific back pain, making a clinical diagnosis difficult. Magnetic resonance imaging (MRI) is the optimal modality for evaluation of suspected vertebral infections. Characteristic MRI characteristics of spine infections include low T1 signal and high T2 signal within the vertebral bodies, high T2 signal within the intervertebral disc, and variable post contrast osseous and disc enhancement. These findings often overlap with noninfectious etiologies, such as degenerative disc disease, inflammatory spondyloarthopathy, neuropathic arthopathy, and hemodialysis associated spondyloarthropathy. Our purpose in this study is to demonstrate that abnormalities with in the psoas musculature, the psoas sign, is strongly associated with lumbar discitis-osteomyelitis and not commonly observed in noninfectious etiologies of lumbar pathology such as degenerative disc disease, inflammatory spondyloarthopathy, neuropathic arthopathy, and hemodialysis associated spondyloarthropathy.  

A retrospective imaging and chart review was preformed of all patients who received a MRI of the lumbar spine in the calendar year of 2013 with the clinical indication or findings that included the key words “infection,” “discitis,” or “osteomyelitis.” Patients were divided into an infectious (23 patients) and noninfectious group (25 patients) based on either biopsy and/or clinical treatment for infection after imaging. Studies were reviewed for presence or absence of abnormal T2 signal and, if available, enhancement within the psoas musculature. Statistical analysis was performed with a two-tailed Fisher’s exact test.  

The infection group showed a positive psoas sign in 21 of 23 patients. The noninfection group had a positive psoas sign in 2 of 25 patients. The association of psoas sign with discitis-osteomyelitis was found to be statistically significant (p <0.05).  

The psoas sign is strongly associated with lumbar discitis-osteomyelitis.

Discitis-osteomyelitis can be a difficult clinical and imaging diagnosis secondary to nonspecific symptoms and imaging findings. A positive psoas sign on MRI can be used as a reliable finding to suggest lumbar discitis-osteomyelitis as opposed to noninfectious etiologies.

Ledbetter, L, Salzman, K, Shah, L, Psoas Sign in Lumbar Vertebral Infections: “Look at Me Lesion!”.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14009838.html