Exploring the Pathogenesis and Treatment Strategies of Post-Herpetic Neuralgia Based on the "Gut-Immune-Neural Axis": A Narrative Review.

Postherpetic neuralgia (PHN) is a prevalent and refractory neuropathic pain condition that arises after herpes zoster infection, characterized by complex pathophysiological mechanisms and limited efficacy of conventional treatments. Recent advances in the study of the gut-brain axis have expanded to encompass pain modulation, leading to the integrated concept of the "gut-immune-neural axis". This narrative review examines the proposed mechanisms by which gut microbiota may contribute to the onset and progression of PHN by modulating immune homeostasis, neuroinflammation, and neural plasticity. We explore the association between gut dysbiosis and PHN, highlighting the pivotal roles of microbial metabolites such as short-chain fatty acids and tryptophan derivatives in mediating these effects. Furthermore, we discuss emerging microbiota-targeted therapeutic strategies that target this axis to improve PHN management. Through a synthesis of current evidence, this narrative review aims to clarify the mechanistic hypotheses linking gut microbiota to PHN and to discuss potential or investigational therapeutic approaches grounded in gut microbiota modulation. It should be acknowledged that direct human evidence in PHN remains limited and largely observational, that much of the mechanistic support is extrapolated from preclinical models and other neuropathic pain conditions, and that the causal role of gut dysbiosis in PHN has not yet been established.