Does Ultrasound-Guided Rectus Sheath Block Reduce Abdominal Pain in Patients with Postherpetic Neuralgia?

To the Editor Postherpetic neuralgia (PHN), one cause of severe neuropathic pain, is believed to result from both peripheral and central sensitization of herpes zoster.1 Clinically, antidepressants and anticonvulsants are recommended as the first line of treatment for PHN.2 However, the analgesic effect of these medications is limited,3 and nerve blocks, including epidural nerve block and root block, are used to reduce the pain and abnormal sensation such as allodynia associated with PHN. We recently treated a patient with PHN on the abdomen by ultrasound-guided rectus sheath block.4 We obtained the patient's written consent to report this case. A 71-year-old man reported 1 year of severe pain on the left side of the abdomen after herpes zoster (T-11 area). He had been treated with antidepressants and anticonvulsants without much success and was referred to our pain clinic. At the initial clinical visit, he complained of a burning, continuous pain on his left abdomen (T-8–T-11 area) with an intensity of 78 mm (out of 100) on a visual analog pain scale. His pain was limited between his anterior axillar line and the midline. The pain increased with movement and touching the area and was severe enough to interfere with his sleep. Mechanical allodynia was also present without any sensory loss at the painful area. After analyzing his clinical course and characteristics, the patient was diagnosed with PHN. Ultrasound-guided rectus sheath block was planned, and with the patient in the supine position, a 22-gauge, 70-mm short bevel nerve block needle (Plexufix®, B. Braun Melsungen AG, Melsungen, Germany) was inserted approximately 5 cm left lateral from his umbilicus under ultrasound guidance using a linear probe (MicroMaxx®, SonoSite Inc., Bothell, WA; HFL38 13 to 6 MHz linear probe), and 20 mL of 0.3% ropivacaine was injected to the periposterior rectus abdominis area. Ultrasonography showed local anesthetic spread between T-7 and T-12 segments. Fifteen minutes after the injection, the patient's spontaneous pain and mechanical allodynia disappeared completely. Analgesia was confirmed between T-8 and T-11 segments by pinprick. At the 1-month follow-up, the patient's pain had reduced to 25 mm on a visual analog pain scale, and mechanical allodynia had decreased. Therefore, an ultrasound-guided rectus sheath block was repeated 3 times at 14-day intervals, after which the pain and mechanical allodynia disappeared completely at the 3-month follow-up. No side effects were observed during the nerve block treatments. Ultrasound-guided rectus sheath block has several advantages in comparison with conventional nerve blocks including epidural nerve block. First, local anesthetics can be directly applied to peripheral nerves in the region of pain. Second, high concentrations of local anesthetics can be used. Third, the spread of applied local anesthetics can be confirmed by ultrasonography. Additional studies including proper controls are needed to confirm efficacy and safety of ultrasound-guided rectus sheath block in patients with abdominal pain due to PHN. Jitsu Kato, MD, PhD Kaname Ueda, MD Yuko Kondo, MD, PhD Mayu Aono, MD Dai Gokan, MD, PhD Miho Shimizu, MD, PhD Setsuro Ogawa, MD, PhD Department of Anesthesiology Nihon University Itabashi Hospital Tokyo, Japan [email protected]