Can persistent pain sustain neuroimmune and COX-dependent signaling?

Persistent nociceptive or neuropathic input occurs within a bidirectional pain–inflammation system: nerve injury and ongoing nociceptor activity can promote immune/glial signaling and prostaglandin-mediated sensitization, while these processes may further amplify pain. The overall claim is biologically credible, with moderate-confidence but mainly associative human support.

Clinical and biomarker evidence

• In a small post-cholecystectomy chronic-pain study, patients with persistent pain and visceral hyperalgesia had higher CSF PGEM—a PGE₂ metabolite—than pain-free controls (3.6 vs 2.1 pg/mL). This supports an association with ongoing central COX-derived eicosanoid signaling, not proof that pain causes it.
• In a 968-person abdominal-surgery cohort, higher postoperative neutrophil-to-lymphocyte ratio was associated with chronic postsurgical pain at one year. Other postoperative inflammatory measures have similarly correlated with later pain persistence, but peripheral blood markers do not establish neural immune activation or causal direction.
• In post-herpetic neuralgia, reported IL-6, IL-18, and CSF IL-8 associations are suggestive but inconsistent; available measures such as CSF cytokines, GFAP, and TSPO-PET are exploratory and not interchangeable indicators of glial activation.

Mechanistic interpretation

• Injured peripheral nerves and dorsal-root ganglia can maintain nociceptor activity, inflammatory signaling, and spinal glial/immune engagement. This provides a coherent pathway for sustained neuroimmune activation.
• COX-generated prostaglandins, especially PGE₂, increase sensory-neuron excitability and contribute to peripheral and spinal sensitization. Injured-nerve COX-2/PGE₂ signaling is therefore a plausible contributor, but not a sole explanation, for chronic neuropathic pain.

Clinical implications

• A placebo-controlled selective COX-2 inhibitor trial in post-herpetic neuralgia showed no significant pain advantage at 3 weeks; low-certainty systematic-review evidence is also insufficient for oral NSAIDs in neuropathic pain. Treatment response therefore cannot validate this mechanism.

Bottom line

• Persistent pain plausibly coexists with and may help sustain neuroimmune and COX/PGE₂ signaling, but human evidence currently supports association and mechanistic plausibility rather than demonstrated causal maintenance.