PATHOPHYSIOLOGY OF RADICULAR PAIN: THE RADICULAR PAIN CASCADE
Radicular pain is characterized by the spreading of the nociceptive input in combination with complex cellular and molecular processes (at the axon and the DRG) that initiate and maintain the increased nociceptive signal input.
In the event of a disc degenerating nerve, the following cascade of events occur:
1. Pro-inflammatory cytokines are released at the site of lesion:
An inflammatory cascade is initiated by the release of inflammatory mediators or Cytokines, such as TNF-α (Tumor Necrosis Factor-alpha)
2. Ectopic or abnormal neuronal firing at the DRG driven by neurotrophins
Once TNF-α reaches the DRG, the production of the neurotrophic factor NGF (nerve growth factor) in the surrounding inflamed tissue is stimulated. NGF triggers the production of another neurotrophic factor: BDNF (brain-derived neurotrophic factor)
3. Ectopic firing at the Dorsal Horn and central pain sensitization
Both NGF and BDNF are also important factors in the development of central sensitization. In other words, they interfere with neuronal excitability and transmission in the dorsal horn; maintaining abnormal pain signaling. Ectopic firing also indices microglia activation
Figure reproduced with permission from Copyright Clearance Center (Van Boxem K et al. Reg. Anesth. Pain Med. 2014;39:149–159).