DIAGNOSTIC ACCURACY OF DIFFUSION-WEIGHTED MRI CLAW SIGN IN DIFFERENTIATING INFECTION FROM DEGENERATIVE MODIC TYPE I SIGNAL CHANGES OF THE SPINE: A CASE-CONTROL STUDY

Abstract

Background: Differentiating spinal infections from degenerative Modic type I signal changes remains a diagnostic challenge due to overlapping imaging features. Diffusion Weighted Imaging (DWI) offers promising potential, particularly through the identification of the “claw sign,” a well-defined linear hyperintensity at the endplate margin indicative of degenerative pathology. Accurately characterizing this sign could improve diagnostic precision, inform clinical decision-making, and reduce misclassification of infectious versus degenerative spinal lesions.

Objective: To assess the diagnostic accuracy of DWI in detecting the “claw sign” and its effectiveness in differentiating spinal infections from degenerative Modic type I signal changes on MRI.

Methods: This prospective case-control study was conducted at the Armed Forces Institute of Radiology and Imaging, Pakistan Emirates Military Hospital, Rawalpindi. A total of 66 adult patients were enrolled—33 with confirmed spinal infections and 33 with degenerative Modic type I changes. All patients underwent standardized spinal MRI protocols, including DWI sequences. Radiological assessments focused on the presence and clarity of the “claw sign,” scored as definite, probable, questionable, or negative. Two independent radiologists, blinded to clinical data, reviewed all imaging. Diagnostic accuracy metrics including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy were calculated. Interobserver reliability was also assessed using Cohen’s kappa.

Results: The “claw sign” exhibited a sensitivity of 97%, specificity of 62%, PPV of 62%, NPV of 69%, and overall diagnostic accuracy of 97%. It was definite in 85% of controls versus 24% of infection cases. Cohen’s kappa showed excellent inter-rater agreement at 0.95. Subgroup analysis revealed slightly lower performance in febrile and neurologically symptomatic patients.

Conclusion: DWI “claw sign” is a highly sensitive, reproducible indicator of degenerative Modic type I changes. Its moderate specificity highlights the need for adjunctive clinical and imaging assessments. Broader validation through multicenter studies is recommended.