POSTHERPETIC neuralgia (PHN) is one of the most difficult problems encountered by physicians.1Sympathetic nerve blockade has been used with variable success as a component of therapy for PHN in cranial, cervical, thoracic, and lumbar distributions. Sacral dermatomal involvement of PHN occurs in only 3% of patients.2To our knowledge, sympathetic blockade of the ganglion impar (Ganglion of Walther) has never been described as a useful therapy for PHN of the sacral dermatomes. We present a patient with PHN in a sacral distribution who had an excellent response to blockade of the ganglion impar using a paramedial approach to the ganglion.
A 74-yr-old woman presented to the pain clinic for evaluation of PHN in the sacral distribution. Her zoster outbreak had occurred 7 months previously with severe rectal and vaginal pain followed several days later by a characteristic cutaneous eruption in the vulvar and perianal distribution. She was diagnosed with acute herpes zoster infection and treated with a course of valacyclovir. Within a few weeks, the cutaneous eruptions cleared; however, the perineal pain persisted. Further evaluation revealed no evidence of gynecologic or rectal abnormalities. Work-up for kidney, bladder, or sexually transmitted infections was negative. She denied any urinary frequency or incontinence. A diagnosis of PHN in the sacral distribution was made, and the patient was treated with Neurontin and tramadol with limited improvement in symptoms.
She was referred to our clinic for further evaluation. Initial physical examination revealed that she sat on one hip on a padded cushion as a result of her discomfort. Examination of the genital and rectal areas revealed no visible abnormalities. She was noted to have allodynia of the external genitalia and in the perirectal area. There were no areas of anesthesia noted. She described her pain as sharp and burning and noted painful bowel movements as well as dyspareunia. She initially received a caudal epidural steroid injection, which gave some mild relief of her symptoms near the coccyx but no relief of her vaginal and rectal pain. On her follow-up visit, she was treated with blockade of the ganglion impar using 12 ml of 0.25% bupivacaine and 40 mg of triamcinolone using a paramedial approach and 22-gauge 3.5-inch spinal needle (Becton-Dickinson, Franklin Lakes, NJ) prepared with two 110-degree bends (fig. 1). She reported immediate relief of her painful symptoms in the perineal area. Telephone follow-up at 1week and 2 and 3 months revealed continued relief of 85–90% of her painful symptoms. She reported that she was able to return to normal activities and only occasionally experienced “minimal” pain in the perineum. At 5-month follow-up, the pain had gradually returned to approximately 80% of the pretreatment level. Repeat blockade of the ganglion impar in the same manner reestablished the pain relief. She has now received three ganglion impar blocks with an average period of relief lasting approximately 5 months. She has been extremely pleased with the results.
Varicella zoster virus, a member of the herpes virus family, is a significant cause of morbidity. The incidence of Varicella (chickenpox) is over 4 million cases per year whereas the incidence of zoster is 300,000 cases per year.3Primary infection with Varicella zoster virus results in Varicella (chickenpox); this is followed by a latent phase where the virus remains sequestered in dorsal root ganglia or the trigeminal ganglion. The virus usually remains dormant; however, it may be reactivated, leading to herpes zoster (shingles). Reactivation may be triggered by infection, immunosuppression, trauma, irradiation, malignancy, and advancing age.4,5Herpes zoster is characterized as severe pain in one or more dermatomes usually followed by a vesicular skin eruption 7 to 10 days later. Persistence of painful symptoms for 4–6 weeks after the termination of the acute phase of infection is referred to as PHN.6Prevalence of PHN is 9–45% of all cases of herpes zoster.7Early institution of sympathetic blockade has been advocated to decrease the incidence and severity of PHN.8,9This therapy remains controversial because a direct correlation between sympathetic blockade and prevention of PHN has not been proven by randomized prospective trials.
The ganglion impar is a solitary retroperitoneal structure. It is the fused terminal end of the paravertebral sympathetic chain and is found at the level of the sacrococcygeal junction (fig. 2). Neural blockade of the ganglion impar has been advocated as a means of managing intractable pelvic and perineal pain in cancer patients.10A review of the literature reveals very limited information on the usefulness of blockade of the ganglion impar for pain other than that of neoplastic origin.
The original technique for blockade of the ganglion impar described by Plancarte and Valazquez10involves a midline approach through the anococcygeal ligament with advancement of the needle tip cephalad to the anterior surface of the sacrococcygeal ligament. This technique involves placing one or two bends near the tip of the needle to more easily approximate the location of the ganglion.10However, a gently curved needle has also been advocated to negotiate around the natural curve of the coccyx.11Insertion of a finger in the rectum has been advocated as a safeguard against perforation of the rectum because it lies in close proximity to the solitary ganglion.10This technique can be quite uncomfortable in a patient with rectal pathology and also makes it difficult to maintain sterility during the procedure. Wemm Jr. and Saberski12advocate passing directly through the sacrococcygeal ligament to reach the ganglion impar. This approach can be useful in patients with normal anatomy but may prove challenging in patients with arthritic changes in the bones and calcification of the ligaments of the sacrum and coccyx. Raj et al .13briefly describe a paramedial approach to the ganglion which we have utilized in our clinic for several years. Huang14recently described a lateral approach to the ganglion approaching from below the transverse process of the coccyx inferior to the level of the sacrococcygeal junction. We believe a paramedial approach to the ganglion impar is a beneficial alternative because this technique does not require insertion of a finger in the rectum and may allow a greater tolerance of the procedure for patients and physicians.
The pain caused by postherpetic neuralgia may involve both peripheral and central mechanisms.1This understanding likely explains why postherpetic neuralgia is so difficult to treat effectively and also stresses the importance of multiple modality therapy.
The role of corticosteroids in pain relief for this patient is uncertain. Corticosteroid injections with nerve blocks have had unpredictable and limited success in treatment of PHN.1Perhaps if further treatment is required for this patient, blockade of the ganglion impar with local anesthetic and no corticosteroid would offer some clarification of the role of corticosteroid in this instance.
Sacral dermatomal distribution of zoster and PHN is unusual but can lead to severe and disabling pain. Blockade of the ganglion impar may play a significant role in treatment of this disabling pain; however, the dramatic results in this patient should be interpreted cautiously. Further investigation is needed to determine efficacy of this sympathetic block in the treatment of the pain of zoster and PHN in the sacral dermatomes. Because of the low incidence of complications with blockade of the ganglion impar, it may have a role in early aggressive therapy of zoster in the sacral dermatomes.
The authors wish to thank Jeff R. Gibson, M.D. (Assistant Professor, Department of Anesthesiology, Scott & White Memorial Hospital, Texas A&M University, Temple, Texas), for valuable comments in the preparation of this manuscript; Bryan Moss (Medical Illustrator, Scott & White Memorial Hospital) for his illustration; Gary Hansen (Corporate Photographer, Scott & White Memorial Hospital) for photography; and Glen Cryer (Publications Manager, Scientific Publications, Scott & White Memorial Hospital, Temple, Texas), Stacy Maness and Julia Blackwell (Medical Editors, Scientific Publications, Scott & White Memorial Hospital, Temple, Texas) for assistance in preparation of this manuscript.