SPECT-CT as a Predictor of Pain Generators for Patients Undergoing Medial Branch Block for Chronic Back Pain

Introduction: The ability to accurately predict pain generators for chronic back pain remains elusive. Medial branch nerve blocks (MBB) are currently used in the diagnosis and management of facetogenic pain. We aimed to evaluate whether SPECT-CT can accurately predict the location of pain generators and if uptake-targeted injections are associated with improved outcomes in patients with chronic back pain.

Methods: A retrospective cohort review was completed on patients having a MBB after SPECT-CT for chronic back pain between 2010 and 2022 at a tertiary academic center. Only patients who had MBB following SPECT-CT were included in this evaluation. Patients undergoing injections at foci of abnormal uptake only were compared with patients undergoing injections of foci with and without uptake as well as only without uptake concerning immediate positive response, visual analog score – VAS.

Results: A total of 428 patients underwent SPEC-CT for chronic back pain. Of those 353, received a MBB following SPEC-CT. A median immediate change in VAS of 4 (IQR=3) was observed (p < 0.01), comparing pre- and post-procedure pain. Multivariable linear regression models found age to be a factor associated with positive response to MBB (regression coefficient 0.02±0.01, p=0.02 and adjusted 0.03±0.01, p=0.01) and patients receiving MBB at foci of radiotracer uptake to have improved outcomes when compared with patients having MBB at foci without uptake (regression coefficient 1.00±0.47, p=0.03 and adjusted 0.99±0.47 p=0.03). In 76 patients a decrease over 70% VAS from baseline was observed with multivariable logistic regression models showing age (adjusted OR=0.05±0.01 p< 0.01) and time to block (adjusted OR=0.03±0.001 p=0.04) as predictive factors of MBB response.

Conclusion : This study suggests there is benefit with use of SPECT-CT to guide MBB and that younger patients and patients with shorter time to treatment after SPECT scans have higher likelihood of a positive response to lumbar medial branch block.