Effectiveness and Durability of Combined Application of Pulsed Radiofrequency and a Steroid to the Dorsal Root Ganglion for Postherpetic Neuralgia: a Randomized Controlled Trial

Varicella-zoster virus reactivates in sensory ganglia as the dorsal root ganglion (DRG). The DRG contains many receptor channels and is an important region for pain signal transduction. Sustained abnormal electrical activity to the spinal cord via the DRG in acute herpes zoster can result in neuropathic conditions such as postherpetic neuralgia (PHN). Postherpetic neuralgia (PHN) is the final stage of varicella-zoster infection and is manifested as severe refractory neuropathic pain. Preventing the transition of herpes zoster-related pain to PHN is a very important therapeutic principle for patients at an early stage, especially for older patients. The exact discriminative time point for PHN has not yet been standardized. Various criteria have been used, from 30 days to 180 days after zoster onset. If pain persists for more than 180 days after zoster onset, the likelihood of pain reduction is very low and such a condition is considered "well established" PHN. Therefore, it is advisable to actively attempt various treatment modalities for pain control before the condition progresses to a recalcitrant state. Pulsed radiofrequency (PRF) is a variant of thermal radiofrequency that applies pulsed current to limit heat generation to less than 42˚C, creating a little risk of thermal or nerve injury. Recently, the use of PRF has increased in many chronic pain conditions, including trigeminal neuralgia, chronic spinal pain, musculoskeletal pain, and it was recently used effectively for postherpetic neuralgia. Transforaminal epidural steroid injection has been proven in previous studies to provide effective analgesia for cases of herpes zoster-related pain. We hypothesize that combined use of pulsed RF and steroid injection applied to the DRG may achieve a better outcome than use of epidural steroid injection alone.