Clinical Concerns Getting to the Bottom of Chronic Post-Surgical Pain Yoram Shir, MD As presented at Thursday Evening Learning Series, McGill University, Montreal, Quebec (March 2006) opulation surveys in the last two decades show that chronic pain is a universal ailment, bringing upon substantial suffering, disability and economic loss. In Canada, almost one third of the adult population suffers from chronic pain.1 While multiple etiologies of chronic pain have been identified and characterized, chronic post-surgical pain (CPSP) is still a neglected area (Table 1). Only recently has it become clear that surgery is a major contributing factor in more than 20% of chronic pain patients attending the pain clinic.3 Moreover, in half of these patients, surgery was the sole factor initiating the chronic pain condition. Unfortunately, there is only limited data on CPSP in the general population. This fact is hard to explain considering our advanced knowledge of pain mechanisms, measurement and treatment modalities. P Larry’s Pain • Larry, 52, is a heavy smoker diagnosed with lung cancer. • He was seen at our Pain Centre eight months after undergoing a thoracotomy and an upper lobectomy of the left lung. • Following the surgery he developed ongoing severe pain in the surgical area. The pain was accompanied by poor sleep and depression. • The treating surgeon and oncologist could not identify a reason for the severe pain. • Initial treatment with non-opioid analgesics and codeine preparations had no affect on the pain. What further treatment options are available? See next page What is the incidence of common CPSP syndromes? CPSP can probably develop after any surgery. However, due to reasons that are not entirely clear, certain surgeries carry higher risk for developing CPSP (Table 2).4 It should be noted that the reported incidence of most CPSP syndromes varies significantly among studies. For example, between 20% to 70% of women undergoing breast cancer surgery report CPSP. This variation probably stems from multiple factors (e.g., retrospective vs. prospective studies, ethnic origin, etc.), some of which are not yet known. Table 1 Definition of post-surgical pain2 • Pain developing after surgery. • Pain persisting for at least two months. • Other causes for pain have been excluded. The Canadian Journal of Diagnosis / May 2006 83 What are the contributing factors for developing CPSP? More on Larry • More than 50% of patients undergoing a thoracotomy are at risk for developing chronic post-thoracotomy pain, similar to Larry. • Treatment at our Pain Center involved pharmacologic and invasive interventions, including amitriptyline, 25 mg at bed time, neurontin 1200 mg per day, strong opioids for a limited period, scar infiltration with local anesthetics, steroids and intercostal blocks. • Six months after initiating treatment, Larry’s pain decreased by 50%, his sleep and mood improved and he was able to resume working on a part-time basis. Table 2 Reported incidence of common chronic post-surgical pain syndromes • Following lumbar spine surgery (failed back surgery syndrome): 15% to 30% • Phantom pain following limb amputation: 30% to 80% • Post thoracotomy: 22% to 67% • Following breast cancer surgery: 20% to 72% Can we decrease acute post-surgical pain? • Gallbladder surgery: 3% to 56% • Inguinal hernia repair surgery: 0% to 54% • Coronary artery bypass grafting: 56% Dr. Shir is an Associate Professor of Anesthesiology at McGill University in Montreal and the Medical Director of the Pain Centre at the McGill University Health Centre, Montreal, Quebec. 84 Multiple presurgical, intrasurgical and post-surgical contributors have been suggested as risk factors for developing CPSP. It is important to recognize the factors that may cause CPSP in order to develop strategies to prevent and/or better treat the problem. The major known contributing factors are listed in Table 3. Of these, severe acute post-surgical pain is the most consistent risk factor for developing CPSP. It is important to realize, however, that not all factors are relevant to each CPSP syndrome. For example, younger age is associated with an increased rate of CPSP in women undergoing breast cancer surgery, but it does not predict an increased risk of CPSP in patients undergoing coronary artery bypass surgery.5 In contrast to one’s expectations, the size of surgery is not necessarily a predictor of increased levels of CPSP. For example, a laparoscopic cholecystectomy is most likely not associated with lower CPSP than open gallbladder surgery. Or, in women with breast cancer, less invasive preservative surgery is associated with higher levels of CPSP, compared to a formal mastectomy.6 Since increased levels of acute post-surgical pain elevate the risk of CPSP, proper postoperative analgesia could be important not only for reducing morbidity and the length of hospitalization, but also to prevent transition into chronicity. Table 4 lists commonly used measures for decreasing acute pain after surgery. Unfortunately, approximately 80% of patients still have pain after surgery, 86% of which report at least moderate pain.7 The Canadian Journal of Diagnosis / May 2006 CPSP What are the current treatment modalities for CPSP? I am not familiar with specific recommendations for treating CPSP. Therefore, these pain syndromes should probably be treated like other chronic pain conditions; treatment should depend on: • the type of pain (e.g., visceral, neuropathic), • pain levels, • previous treatment modalities and • other medical conditions (Table 5). Currently, there is practcally no data on the long-term prognosis of these patients, or on the success rate of their treatment. Table 3 Possible contributing factors for developing chronic post-surgical pain • Younger age • Increased preoperative pain • High preoperative depression and anxiety • Surgical technique • Severe acute post-surgical pain Table 4 Commonly used analgesic measures for acute post-surgical pain • Medications: non-opioids, opioids Can we decrease the incidence of CPSP in the future? It is a well accepted fact that efforts aimed at preventing CPSP have a better chance of decreasing the incidentce of CPSP than treating it once it has already developed. Prevention can be achieved in two ways: 1. Identifying predictors for CPSP At present, we cannot predict which patients will develop severe pain after experiencing trauma or undergoing surgery. It is possible, however, that preoperative differences in pain sensitivity could predict post-surgical pain. Indeed, preliminary psychophysical studies indicate that increased preoperative pain levels, in response to painful pressure, (i.e., hot and cold stimuli) were significantly associated with increased post-surgical pain.8 It is possible then, that normal responses, prior to injury, could predict the intensity of acute and chronic pain after surgery. The ability to identify patients at higher risk for developing CPSP • Wound infiltration with local anesthetics • Peripheral nerve blocks • IV patient-controlled analgesia with opioids • Epidural analgesia Table 5 Treatment of chronic postsurgical pain • Pharmacotherapy: - Non-opioid analgesics - Adjuvant medications (e.g., antidepressants, antiepileptics) - Opioids • Physical modalities: - Physiotherapy and rehabilitation - TENS • Invasive interventions: - Nerve blocks - Ablative procedures • Psychological and behavioral approach TENS: Trans-cutaneous electrical nerve stimulation The Canadian Journal of Diagnosis / May 2006 85 before surgery will hopefully enable the early use of more aggressive analgesic measures. 2. Developing preventive analgesic measures Although still controversial, there are indications that aggressive analgesic interventions provided before surgery could prevent the alterations in sensory processing. The alterations in sensory processing amplify postinjury pain and lead to chronicity. Presurgical interventions (e.g., continuous use of epidural anesthesia and analgesia) could decrease the incidence of chronic post-surgical pain.9 Dx References 1. Moulin D, Clarke A, Speechley M, et al: Chronic pain in Canada prevalence, treatment, impact and the role of opioid analgesia. Pain Res Manag 2002; 7(4):179-84. 2. Macrae W: Chronic pain after surgery. Br J Anaesth 2001; 87(1):88-98. 3. Crombie I, Davies H, Macrae W: Cut and thrust: Antecedent surgery and trauma among patients attending a chronic pain clinic. Pain 1998; 76(1-2):167-71. 4. Perkins F, Kehlet H: Chronic pain as an outcome of surgery. Anesth 2000; 93(4):1123-33. 5. Macdonald L, Bruce J, Scott N, et al: Long-term follow-up of breast cancer survivors with post-mastectomy pain syndrome. Br J Cancer 2005; 92(2):225-30. 6. Tasmuth T, von Smitten K, Kalso E: Pain and other symptoms during the first year after radical and conservative surgery for breast cancer. Br J Cancer 1996; 74(12):2024-31. 7. Apfelbaum J, Chen C, Mehta S, et al: Postoperative pain experience: results from a national survey suggest postoperative pain continues to be undermanaged. Anesth Analg 2003; 97(2):534-40. 8. Granot M, Lowenstein L, Yarnitsky D, et al: Postcesarean section pain prediction by preoperative experimental pain assessment. Anesth 2003; 98(6):1422-6. 9. Obata H, Sarto S, Fujita N et al: Epidural block with mepivacaine before surgery reduces long-term post-thoracotomy pain. Can J Anesth 1999; 46(12):1127-32. 86 Take-home message • Chronic post surgical pain is an under recognized, prevalent and a debilitating public health problem. • Current clinical practices are not sufficient to prevent the development of chronic post-surgical pain. • Preventive measures and early aggressive interventions should be developed. • The primary physician should have a central role in early detection and treatment of this problem. The Canadian Journal of Diagnosis / May 2006