Introduction
Postherpetic neuralgia (PHN) is a debilitating condition that is often interfering daily life of patients. 
The erector spinae plane block (ESPB) is a myofascial plane block first introduced in 2016 for treating thoracic neuropathic pain. 
Recently, several studies have reported evidence for the efficacy of ESPB in the management of thoracic neuropathic or postoperative pain. 
The resolution of neuropathic pain after ESPB suggests that both dorsal and ventral rami of thoracic spinal nerves are affected by local anesthetic and it is thought to be the main mechanism of analgesia. 
We present a case of pain reduction after ESPB in thoracic PHN which has been showed poor response to other treatments.

Case Presentation
Present Illness 
A 43-year-old woman visited our pain clinic with a chronic pain of right lower thoracic region started four years ago after herpes zoster. She suffered from burning and stabbing pain with NRS from 3 to 7 out of 10, mainly at T9 dermatomes. Physical examination revealed allodynia and hyperesthesia over the affected dermatomes. 
She had received various medications including pregabalin, nortriptyline HCL and alprazolam and thoracic epidural steroid injections (ESI) at other hospital. However, there was no significant improvement. 
We performed ESI in the T9/10 interlaminar space, and one month later, a transforaminal ESI at the right T9 level with the diagnosis of PHN. In spite of reduction of pain, she still reported that there was interference of daily life. 
Then, we planned an ultrasound guided thoracic ESPB at the level of T9 in the right side and performed as follows.

 Procedure
After the patient was prone positioned, we sterilized her skin with the alcohol swab. 
The ultrasound (Sonosite M-Turbo®) probe with 13 MHz was installed in a longitudinal orientation on the spinous process, and we counted the spinous process from T12 to T9.  
After finding the spinous process of T9 in a longitudinal orientation, the ultrasound moved the probe right laterally to discover the transverse process. Then, we rotated the US probe 90 degrees. As a consequence, the trapezius muscle, the latissimus dorsi muscle, the erector spinae muscle, and the transverse process were visualized (Fig 1).
The 26 gauge, 2 inch needle was inserted in-plane technique until touching transverse process. We injected the 0.375% ropivacaine 25 cc in the fascial plane. There was no complication during and after the procedure.
 Post procedure progress.
During a follow-up of three months, she reported a significant resolution of symptoms, with a NRS from 0 to 2 out of 10, and was in good condition. 
Furthermore, she said that ESPB was the most effective treatment she had ever received.

Conclusion
This is the first reported case of using ESPB for management of refractory PHN in pain clinic. 
Randomized controlled studies are required to prove efficacy of ESPB on PHN patient and to determine the optimal volume and dose.

ERECTOR SPINAE PLANE BLOCK IN THE MANAGEMENT OF POSTHERPETIC NEURALGIA