Extracorporeal Shock Wave Lithotripsy and Endotherapy for Pain in Chronic Pancreatitis

Pain is the predominant symptom in patients with chronic pancreatitis (CP) and remains a considerable therapeutic challenge. In patients with pathological changes of the pancreatic duct, including stones and strictures, endoscopic procedures with or without preceding extracorporeal shock wave lithotripsy (ESWL) and surgery have been used with varying success to treat pain. The rationale for endoscopic therapy or surgical drainage procedures is based on the hypothesis that obstruction of the pancreatic duct leads to ductal hypertension and pain. However, clinical pain symptoms correlate poorly with pancreatic ductal morphology and the response to endoscopic or surgical treatment is unpredictable, with long term response rates ranging from 30-60%. The evidence for these treatments are, however, based on case-series and comparison between different procedures, while no prospective sham controlled trials have evaluated the effectiveness of invasive treatments for pain in CP. In addition, a marked placebo effect has been observed in most trials of painful CP and this, together with the natural history of disease, needs consideration when treatment effects are evaluated. Therefore, the rationale behind invasive treatments for pain in CP treatments can be questioned.

Recent meta-analyses have documented that the non-specific effects of surgery and other invasive procedures are generally large; particularly in the field of pain-related conditions. For example, arthroscopic meniscectomy for degenerative meniscal lesions has for many years been considered the state of the art treatment for this common condition. However, a high quality randomized controlled trial (RCT) and meta-analysis have not shown any differences in pain relieving effects between surgery and sham procedures for degenerative meniscal lesions. These findings challenge conventional wisdom and underline the necessity of properly conducted RCTs including a sham procedure, when the effectiveness of invasive procedures is evaluated.

Albeit endoscopic therapy or surgery are widely used for pain in CP these treatments are only effective in a subset of patients. An improved understanding of the mechanisms underlying pain in CP suggest that the pain etiology in most patients is multifactorial and, in addition to the proposed mechanical mechanisms for pain (ductal obstruction/hypertension), a large body of evidence support a ´neuropathic pain phenotype´ with abnormal processing in the peripheral and central neural pathways. This likely explains the variable response to endoscopic and surgical treatments and underline an unmet need for biomarkers to identify responders to the different treatment modalities.

Quantitative sensory testing (QST) can be used to investigate the state of the pain system; the technique is based on the rationale that different neural pathways and networks can be explored using standardized stimulation with simultaneous recording of the evoked pain response by psychophysical and/or objective methods. Due to spinal convergence between visceral afferents from the pancreas and somatic afferents from the Th10 skin dermatome, somatic QST can be reliable used to assess if the pain system is locally sensitized by nociceptive input from the pancreas (segmental sensitization). However, in many patients with chronic pain the pain system has become dysfunctional and has undergone a more universal sensitization. In such cases the QST profile of testing in several dermatomes together with specific test paradigms (temporal summation and assessment of descending inhibition) can be used to determine whether patients have abnormal central pain processing.

The hypothesis of the present study is that combined ESWL and endotherapy induce short term (3 months) and mid-term (6 months) pain relief in patients with CP compared to a sham procedure. In addition, the investigators hypothesize that QST can be used to predict the outcome of combined ESWL and endoscopic therapy. Hence, patients with evidence of abnormal pain processing are hypothesized to have a worse outcome to treatment compared to patients with segmental or no evidence of sensitization.