An Investigation of the Effect of Pulsed Radiofrequency Treatment of the Dorsal Root Ganglion on Cerebrospinal fluid, peripheral venous blood and DRG washings in patients with chronic lumbosacral radicular pain

Abstract

The objective of this thesis is to investigate alterations in the cellular and peptide composition of cerebrospinal fluid, blood, DRG washings and saliva in patients with a diagnosis of chronic lumbar radicular pain scheduled for treatment with pulsed radiofrequency (PRF) therapy to the appropriate DRG level. The rationale for choosing this model lies with several factors: firstly, that CNP is a centrally mediated neural phenomenon and secondly that PRF is an effective treatment thereby suggesting that it interferes with the mechanism of CNP in vivo. Therefore, this work will elucidate the effect of PRF on these specimens. CNP is a challenging clinical problem, and a major component of this challenge relates to lack of an objective measurement and reliance on self-reporting. The possibility of establishing a link between the CSF and DRG washings and saliva and/or peripheral blood would open the door to possible biomarker development. DRG washings were obtained as the DRG is outside the CNS allowing a comparator of peripheral to central transmission. Pulsed radiofrequency therapy is a non-ablative pain treatment, which delivers radiofrequency current in short high-voltage bursts to a neuronal dorsal root ganglion (DRG) resulting in interruption of nociceptive afferent pathways. It is accepted the pathophysiology of chronic neuropathic pain (CNP) has a neuroimmune basis. However, the exact mechanisms of available therapies such as PRF is still not known. PD-1 is an immune checkpoint inhibitor, found on activated T-cells which functions by inhibiting both adaptive and innate immune systems. Binding of PD-1 to PD-L1, which is a ligand found on tumour cells creates a complex which inhibits the body's own T-cell mediated response and allows proliferation of tumours. It is known that cancers such as non-small cell lung cancer and metastatic melanoma can remain painless during proliferation stage. Pain presents only at an advanced stage such as bony metastasis. Presence of a PD-1/PD -L1 complex has been suggested as a mechanism of this 'pain-silencing'. Identification of PD-1 in patients with chronic pain may suggest a novel pain pathway that has not been investigated to date. Additionally, alterations in this complex post PRF suggests a potential target for therapy in the future. It has been suggested that pathogenic B cells may influence the development of chronic pain. Several controlled clinical trials have shown that B-cell-targeted therapy with rituximab is effective in patients with rheumatoid arthritis and significantly alleviates their pain. Evidence available for chronic neuropathic pain and the role of B lymphocytes is purely preclinical at present. Comparison of different physiological human samples pre- and post-therapy would allow more detailed characterisation of the effects of PRF; as well as providing information which may enhance our understanding of the pathophysiology of neuropathic pain. Methods Ethical approval was obtained. This study involved taking cerebrospinal fluid, DRG washings, saliva and blood samples before and after PRF treatment. The cellular characteristics of CSF, peripheral blood and saliva T and B cells in addition to neuropeptides and proteome were determined using Flow Cytometry, ELISA and Mass Spectrometry. Patients were screened for neuropathic pain at outpatient clinics at Hermitage Medical Clinic, Dublin and enrolled according to strict inclusion/exclusion criteria of the individual study. Lumbar radicular pain was the required diagnosis for enrolled patients. Demographics and pain scores according to numerical rating scale (NRS) were recorded. A post treatment sample was taken 12 weeks after treatment, in addition to outcome data. We compared the pre and post intervention samples in addition to clinical pain assessment. In vitro work was also performed to examine the effect of PRF on T cells directly. Results Clinically, 75% of patients recruited had a positive outcome post procedure. This was >50% improvement in their chronic pain. In this cohort of patients with lumbar radicular pain who were deemed responders to PRF, a statistically significant alteration in CD4+ Pre-treatment (pre) CSF and Post-treatment(post) DRG was observed (p value 0.0239). A statistically significant alteration in CD8+ pre-DRG vs Pre-CSF was observed (p value 0.0387). A statistically significant difference between CD8+ PD1+ pre-CSF vs post-DRG was observed (p value 0.035). There was no significant corresponding alteration in blood or saliva T-lymphocyte quantification or PD-1/PD-L1 expression. A new finding is presence of T-lymphocytes in DRG washings both pre and post therapy. This has not been reported before. Conclusion: Although effective, PRF therapy did not achieve full remission of symptoms in any patient. Evidence of immunomodulation was present mostly in CSF and also DRG washings without significant alterations seen in blood or saliva. Pre-treatment CSF and post-treatment DRG T-lymphocyte quantification were altered post treatment. Immune checkpoint inhibitors were also altered significantly suggesting PD-1/PD-L1 plays a role in CNP pathogenesis. The chronicity of pain in humans is inherently complex but advances in technology with CSF analysis and neuroimaging in conjunction with sham/placebo-controlled trials will enable better phenotyping of patients and a better understanding of treatment mechanisms and the pathophysiology of neuropathic pain.