Dear Editor, We present findings from a longitudinal, prospective study that examined the long-term efficacy of ultrasound-guided injection of incobotulinumtoxinA in six patients with piriformis syndrome. Characterized by buttock pain corresponding to the anatomical location of the piriformis muscle that varies according to patient position or activity, piriformis syndrome is a rare and poorly defined disorder—often still included in the broad definition of lower back pain . While etiology is not well established, the most accepted pathophysiologic factor in piriformis syndrome is compression of the sciatic nerve, which passes below and through the piriformis muscle. In the absence of a specific test, piriformis syndrome is primarily diagnosed on the basis of clinical symptoms, physical examination, and a positive response to local injection of anesthetic into the muscle . Conservative treatment of piriformis syndrome involves the use of analgesics, anti-inflammatory drugs and muscle relaxants, physical therapy, and intramuscular injection of corticosteroid and/or local anesthetics, guided by various imaging techniques. However, the operational complexity of guidance techniques such as fluroscopy and electromyography can limit their clinical usefulness . Ultrasound-guided injection offers process simplification in tandem with efficient, localized delivery of the injected drug , although clinical evidence to support its efficacy, safety, and precision for performing piriformis injections is currently lacking. Recently, injection of botulinum toxin into the piriformis muscle has shown promise in the management of piriformis syndrome [5–9]. We look to build upon this evidence base by establishing the long-term efficacy of incobotulinumtoxinA treatment, extending the duration of follow-up from the 12 to 16 weeks used in clinical trials to date [6,8,10] to six months. Our study, conducted at the Physical Medicine and Rehabilitation Department of the Hospital Virgen Macarena, Seville, Spain, assessed the efficacy, safety, and precision of a single ultrasound-guided injection of 100 U incobotulinumtoxinA (Xeomin; Merz Pharmaceuticals GmbH, Frankfurt am Main, Germany; in 2 mL saline) into the piriformis muscle of adults with chronic buttock or sciatic pain clinically compatible with piriformis syndrome. The study received relevant ethical approval. IncobotulinumtoxinA dose selection was based on previous studies of botulinum toxin for piriformis syndrome, which have used doses of 40 U incobotulinumtoxinA (case study), 50 to 100 U onabotulinumtoxinA, 150 to 200 U abobotulinumtoxinA, and 5,000 to 12,500 U rimabotulinumtoxinB . Patients were recruited on the basis of treatment-refractory buttock pain in the anatomical area of the piriformis muscle on selective finger palpation and at echopalpation, a pain score of 5 or higher out of 10 on a visual analog scale (VAS), and over three months of pain progression. Patients undergoing treatment with anticoagulants, with neurologic focality at the lower homolateral limb diagnosed as impairment of osteotendon reflexes or loss of strength, and the presence of other pathologies causing muscle weakness were excluded. In total, 24 patients (mean age = 57.0 years, SD = 12.6 years, 83.3% female) were recruited. Of these, only six (25.0%) attended with a correct diagnosis of piriformis syndrome, with sciatica (41.7% of patients) and chronic lower back pain (33.3%) accounting for misdiagnoses. Localization of the injection site was determined as described previously . The piriformis muscle appeared as a hypoechoic band-shaped mass on a hyperechoic image that corresponded to the sciatic recess (Figure 1). Poor needle imaging due to depth and inclination, an acknowledged difficulty with ultrasound-guided injection techniques, and limited visualization of the sciatic nerve (six cases, 25.0%) were the main technical difficulties encountered. Complications associated with the injection procedure were acute, self-limiting sciatica (one patient) and postinjection pain (four patients). Figure 1 View largeDownload slide Ultrasound image of the piriformis muscle. A Mindray M–7 ultrasound with a convex transducer at 5 to 7.5 MHz frequency was used. The piriformis muscle appears as a hypoechoic band on a hyperechoic image corresponding to the iliac fossa. GM = gluteus maximus; GSN = great sciatic notch; PM = piriformis muscle; SCT = subcutaneous tissue; SN = sciatic nerve. Figure 1 View largeDownload slide Ultrasound image of the piriformis muscle. A Mindray M–7 ultrasound with a convex transducer at 5 to 7.5 MHz frequency was used. The piriformis muscle appears as a hypoechoic band on a hyperechoic image corresponding to the iliac fossa. GM = gluteus maximus; GSN = great sciatic notch; PM = piriformis muscle; SCT = subcutaneous tissue; SN = sciatic nerve. Patients perceived an improvement in chronic pain intensity and quality of life (QoL) for up to six months after treatment with 100 U incobotulinumtoxinA, as evidenced by statistically significant reductions in VAS pain scores and significant improvements in pain-related QoL based on the Lattinen Index (LI; validated in Spanish ) at one and six months following treatment (P < 0.05, Bonferroni test for comparison of means) (Figure 2). At six months, all patients achieved predefined responder thresholds (≥50% score reduction from baseline) for both VAS and LI scores, with a significant correlation between the two (Spearmann correlation coefficients of 0.80 and 0.90 for months 1 and 6, respectively). The LI items that showed the greatest reduction in scores were degree of disability and sleep duration, suggesting that these were directly related to patient-perceived improvement in QoL. Six months after incobotulinumtoxinA injection, half of the patients were asymptomatic and the remainder reported feeling better; no patients reported unchanged or worsening symptoms. IncobotulinumtoxinA injections were well tolerated, and no adverse reactions were reported. Figure 2 View largeDownload slide Pain and QoL improvements after botulinum toxin treatment. A) Mean (SD) VAS score, range from 0 (no pain) to 10 (severe pain). B) Mean (SD) LI score of QoL in chronic pain, range from 0 (no impairment) to 20 (severe effect on QoL by pain). *Significant reductions (P < 0.05 Bonferroni test for comparison of means) in VAS and LI scores were found between baseline and one month post-treatment and baseline and six months post-treatment. LI = Lattinen Index; QoL = quality of life; VAS = visual analog scale. Figure 2 View largeDownload slide Pain and QoL improvements after botulinum toxin treatment. A) Mean (SD) VAS score, range from 0 (no pain) to 10 (severe pain). B) Mean (SD) LI score of QoL in chronic pain, range from 0 (no impairment) to 20 (severe effect on QoL by pain). *Significant reductions (P < 0.05 Bonferroni test for comparison of means) in VAS and LI scores were found between baseline and one month post-treatment and baseline and six months post-treatment. LI = Lattinen Index; QoL = quality of life; VAS = visual analog scale. The use of ultrasound guidance for incobotulinumtoxinA injection into the piriformis muscle reduced the technical complexity of the injection procedure in comparison with other conventionally used guidance techniques without increasing the incidence of complications or reducing the overall effectiveness of the procedure. That the procedure required only a single consultation without any need for irradiation has positive implications with respect to resource utilization in clinical practice. However, such promise must be countered by the fact that accurate localization of the piriformis muscle requires expertise in order to avoid injury to the sciatic nerve. Given the higher cost of botulinum toxin compared with that of local anesthetics  and the risk of muscle atrophy and fat generation that has been reported following botulinum toxin injection in piriformis syndrome , we acknowledge that this treatment approach may be most relevant for those patients with a level of disease that has proven refractory to previous treatment approaches. In conclusion, these results support the use of ultrasound-guided injection of 100 U incobotulinumtoxinA for the long-term management of treatment-refractory piriformis syndrome, suggesting that, with adequate clinical examination, the diagnostic need for an initial conservative injection of anesthetics may be eliminated. However, given the limited sample size, we acknowledge that further investigation is warranted before firm conclusions can be drawn, particularly regarding the lowest effective dose of incobotulinumtoxinA and the cost-effectiveness of such an approach. Acknowledgments The authors would like to thank the study patients and investigators. This study and the editorial support were funded by Merz Pharmaceuticals GmbH, Frankfurt am Main, Germany, with an unrestricted grant. Editorial support in the preparation of this manuscript (editing for English language) was provided by Claire Cairney (PhD) of Complete Medical Communications. References 1 Niu CC, Lai PL, Fu TS, Chen LH, Chen WJ. Ruling out piriformis syndrome before diagnosing lumbar radiculopathy. Chang Gung Med J 2009; 32: 182– 7. Google Scholar PubMed 2 Misirlioglu TO, Akgun K, Palamar D, Erden MG, Erbilir T. Piriformis syndrome: Comparison of the effectiveness of local anesthetic and corticosteroid injections: A double-blinded, randomized controlled study. Pain Physician 2015; 18: 163– 71. Google Scholar PubMed 3 Fishman SM, Caneris OA, Bandman TB, Audette JF, Borsook D. Injection of the piriformis muscle by fluoroscopic and electromyographic guidance. Reg Anesth Pain Med 1998; 23: 554– 9. Google Scholar PubMed 4 Smith J, Hurdle MF, Locketz AJ, Wisniewski SJ. Ultrasound-guided piriformis injection: Technique description and verification. Arch Phys Med Rehabil 2006; 87: 1664– 7. Google Scholar CrossRef Search ADS PubMed 5 Benzon HT, Katz JA, Benzon HA, Iqbal MS. Piriformis syndrome: Anatomic considerations, a new injection technique, and a review of the literature. Anesthesiology 2003; 98: 1442– 8. Google Scholar CrossRef Search ADS PubMed 6 Lang AM. Botulinum toxin type B in piriformis syndrome. Am J Phys Med Rehabil 2004; 83: 198– 202. Google Scholar CrossRef Search ADS PubMed 7 Childers MK, Wilson DJ, Gnatz SM, Conway RR, Sherman AK. Botulinum toxin type A use in piriformis muscle syndrome: A pilot study. Am J Phys Med Rehabil 2002; 81: 751– 9. Google Scholar CrossRef Search ADS PubMed 8 Fishman LM, Anderson C, Rosner B. Botox and physical therapy in the treatment of piriformis syndrome. Am J Phys Med Rehabil 2002; 81: 936– 42. Google Scholar CrossRef Search ADS PubMed 9 Porta M. A comparative trial of botulinum toxin type A and methylprednisolone for the treatment of myofascial pain syndrome and pain from chronic muscle spasm. Pain 2000; 85: 101– 5. Google Scholar CrossRef Search ADS PubMed 10 Yoon SJ, Ho J, Kang HY, et al. Low-dose botulinum toxin type A for the treatment of refractory piriformis syndrome. Pharmacotherapy 2007; 27: 657– 65. Google Scholar CrossRef Search ADS PubMed 11 Santamato A, Micello MF, Valeno G, et al. Ultrasound-guided injection of botulinum toxin type A for piriformis muscle syndrome: A case report and review of the literature. Toxins (Basel) 2015; 7: 3045– 56. Google Scholar CrossRef Search ADS PubMed 12 Chan CW, Peng P. Ultrasound-guided blocks for pelvic pain. In: Narouze SN, ed. Atlas of Ultrasound Guided Procedures in Interventional Pain Management . New York: Springer-Verlag; 2010: 207– 24. 13 González-Escalada JR, Camba A, Muriel C, et al. Validación del índice de Lattinen para la evaluación del paciente con dolor crónico. Rev Soc Esp Dolor 2012; 19: 181– 8. 14 Graboski CL, Gray DS, Burnham RS. Botulinum toxin A versus bupivacaine trigger point injections for the treatment of myofascial pain syndrome: A randomised double blind crossover study. Pain 2005; 118: 170– 5. Google Scholar CrossRef Search ADS PubMed 15 Al-Al-Shaikh M, Michel F, Parratte B, et al. An MRI evaluation of changes in piriformis muscle morphology induced by botulinum toxin injections in the treatment of piriformis syndrome. Diagn Interv Imaging 2015; 96: 37– 43. Google Scholar CrossRef Search ADS PubMed © 2017 American Academy of Pain Medicine. All rights reserved. For permissions, please e-mail: email@example.com
Pain Medicine – Oxford University Press
Published: Feb 1, 2018
It’s your single place to instantly
discover and read the research
that matters to you.
Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.
All for just $49/month
Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly
Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.
Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.
Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.
All the latest content is available, no embargo periods.
“Hi guys, I cannot tell you how much I love this resource. Incredible. I really believe you've hit the nail on the head with this site in regards to solving the research-purchase issue.”Daniel C.
“Whoa! It’s like Spotify but for academic articles.”@Phil_Robichaud
“I must say, @deepdyve is a fabulous solution to the independent researcher's problem of #access to #information.”@deepthiw
“My last article couldn't be possible without the platform @deepdyve that makes journal papers cheaper.”@JoseServera