Background: Chronic pain usually accompanied by tissue damage and inflammation. However, the pathogenesis of chronic pain remains unclear. Methods: We investigated the role of nerve growth factor (NGF) in chronic inflammatory pain induced by complete Freund's adjuvant (CFA), explored the methylation status of CpG islands in the promoter region of the NGF gene, and clarified the function and mechanism of C/EBPα-NGF signaling pathway from epigenetic perspective in the chronic inflammatory pain model. Results: CFA induced significant hyperalgesia and continuous upregulation of NGF mRNA and protein levels in the L4-6 dorsal root ganglions (DRGs) in rats. Hypomethylation of CpG islands occurred in the NGF gene promoter region after CFA treatment. At the same time, the miR-29b expression level was significantly increased, while the DNA methyltransferase 3b (DNMT3b) level reduced significantly. Moreover, CFA treatment promoted binding of C/ EBPα to the NGF gene promoter region and C/EBPα siRNA treatment obviously decreased expression of NGF levels and also alleviate inflammatory hyperalgesia significantly in rats. Conclusion: Collectively, the results indicated that CFA leads to the upregulation of miR-29b level, which represses the expression of DNMT3b, enhances the demethylation of the NGF gene promoter region, and promotes the binding of C/EBPα with the NGF gene promoter, thus results in the upregulation of NGF gene expression and maintenance of chronic inflammatory pain.

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An ultrasound-guided thoracic paravertebral nerve block was administered for left-sided abdominal pain. Lidocaine 0.4% (9.5 mL) was injected. Spinal anesthesia developed after the injection that resolved after 3 hours. One week later, a magnetic resonance imaging scan of thoracic spine identified a left T10 nerve root sheath cyst. It was postulated that the local anesthetic was injected into the cyst, which communicated with the subarachnoid space. This case report demonstrates the anatomic variations of nerve root sheath cyst sites and the risk of injection into intranerve root sheath cysts during interventional procedures.