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Diffusion-Weighted Mri (Dwi) ‘Claw Sign’ Is Useful In Differentiation Of Infectious From Degenerative Modic I Signal Changes Of The Spine 2013

Category General Spine Keyur Patel, MD
Michael Poplawski
Puneet Pawha, MD
Bradley Delman
Thomas Naidich
Lawrence N. Tanenbaum, MD, FACR
Purpose Modic signal changes, a common observation in MR imaging, are signal intensity findings in vertebral body marrow adjacent to the endplates of degenerative discs. Type II and III patterns are easy to recognize and indicative of chronic degenerative disease. Type I Modic change is more likely to be clinically symptomatic and characterized by decreased signal on T1WI and increased signal on T2WI that can be difficult to differentiate from and often suggestive of vertebral osteomyelitis and discitis(1). Of late, diffusion-weighted MR imaging (DWI) has been shown to be a useful tool in imaging of osseous and epidural spinal lesions, including spinal infection (2). In this retrospective observational study of patients who were referred for spinal MRI, we characterize and correlate the MRI appearance of spinal levels in patients with Modic I signal changes, and in patients with confirmed spinal infection, with particular attention to the presence or absence of the DWI “claw sign”.
Materials & Methods Seventy four patients with Modic I type endplate abnormalities were selected and classified into three groups: clinically confirmed discitis/osteomyelitis (n=21), degenerative Modic I change (n=33), and suggestive of infection but clinically disproved (n=20). Each abnormal spinal level was evaluated in terms of MR endplate and disc signal changes, enhancement, and appearance on DWI (b value of 500s/mm2). The presence of diffusion “claw sign” was scored on a scale of 1=definite, 2=probable, 3=questionable, 4=absent (diffuse DWI signal). Results Type I changes in the absence of infection invariably correlated with a characteristic DWI “claw sign” of high diffusion signal at the boundary of the proliferative marrow process and the normal marrow, while patients with type I Modic  signal and confirmed spondylodiscitis exhibited significant absence of the “claw sign” on DWI(average “claw” scoreof 1.21±0.07vs. 3.67±0.17, p<0.01).  Similarly, the group in which infection was initially suggested, but subsequently discounted, had an average score of 1.45±0.13. Suggestion of infection seemed to be related to the presence of high T2 signal in the disc space, which in this study had a high sensitivity, but low specificity for infection. On the other hand, absence of the “claw sign” (combined score 3 and 4) had a high sensitivity (90%), specificity (98%) and predictive values for infection.
Conclusion DWI offers powerful characterization information in patients with Type I Modic MR signal changes and assists in the differentiation of degenerative disease from spondylodiscitis of the spine.
References 1. Dunbar JA, Sandoe JA, Rao AS, et al. The MRI appearances of early vertebral osteomyelitis and discitis. Clin Radiol. 2010 Dec; 65(12):974-81. Epub 2010 Jul 7. 2. Eguchi Y, Ohtori S, Yamashita M,et al. Diffusion magnetic resonance imaging to differentiate degenerative from infectious endplate abnormalities in the lumbar spine. Spine (Phila Pa 1976). 2011 Feb 1;36(3):E198-202.