Role of magnetic resonance imaging and 18-fluorodeoxyglucose positron emission tomography-computed tomography in identifying pain generators in patients with chronic low back pain
Authors: Sharma Deepak Nandkishore , Yerramneni Vamsi Krishna , Srivastava Madhur Kumar , Yerragunta Thirumal , Akurati Sasank 
Published: November 2023

Objective:
Low back pain (LBP) is a major cause of pain and disability. Identification of the pathology accurately or the pain generators is sometimes difficult with the conventional modalities such as magnetic resonance imaging (MRI), computed tomography (CT), or X-ray. Nuclear medicine investigations such as single-photon emission CT (SPECT/CT) or 18-fluorodeoxyglucose positron emission tomography-CT (18-FDG PET-CT) have emerged as an adjuvant tool in these cases. In this study, we evaluated and analyzed the role of 18-FDG PET-CT in identifying active pain generators and the outcomes of interventions based on that compared to MRI.

Methodology:
This study included all patients who fell under inclusion criteria presented with chronic LBP with or without radiculopathy. History and clinical examination were done as well as Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) scores were calculated. All the patients underwent MRI lumbosacral spine with sacroiliac (SI) joint and 18-FDG PET-CT whole spine. Patients in whom PET-CT was positive and active pain generator was identified were managed for the specific level or pain generator responsible by appropriate modalities, i.e. surgery, interfacetal injections, transforaminal epidural injections, and SI joint injections. Patients in whom PET-CT was negative were managed according to the pain generator identified on the basis of MRI and clinical correlation. Patients were told to follow-up after 1 week and 1 month, and subsequent improvement was evaluated on the basis of VAS after 1 week and 1 month and ODI score after 1 month.

Results:
A total of 20 patients were included in the study, with a mean age of 41.9 ± 13.53 years. Twelve patients had multiple level pathology without the indication of significant pain generator and eight patients’ symptoms did not correlate with the MRI findings. 18-FDG PET-CT was done in all patients. 10% (2/20) patients were identified with active pain generators on PET-CT which were not identified on MRI. Eleven out of twenty patients underwent intervention in the form of surgery or pain injections. The mean VAS and ODI score in the patients intervened on the basis of 18-FDG PET-CT improved by 70.59% and 50%, respectively, whereas in patients who underwent intervention on the basis of MRI had improvement in mean VAS and ODI score by 58.57% and 30.81%, respectively after 1 month.

Conclusion:
Inflammation and associated degenerative process in the spine is a continuous process and affects multiple levels and might not be easily picked up on MRI or other conventional modalities. Thus, 18-FDG PET-CT is useful in identifying these active inflammatory processes and thereby helping in the localization of active pain generators. Treating these active pain generators has a better outcome in patients after intervention in terms of better pain relief and quality of life and also reduces the levels being treated.