Outcomes and Predictors of Ultrasound Guided Trigger Point Injections for Chronic Abdominal Wall Pain

Abstract

Purpose: Chronic abdominal wall pain (CAWP) is reported to account for up to 30% of cases of chronic abdominal pain. Diagnosis relies upon history and identifying a focal area of tenderness with a positive Carnett's test (CAWP increases with tensing rectus abdominis). Ultrasound guided trigger point injection (TPI) with local anesthetic is used as a treatment of CAWP, however, little is known about outcomes of this treatment. The aim of this study was to determine the effectiveness of ultrasound guided TPI and predictors of a successful TPI. Methods: Patients receiving TPI between July 1 2010-June 30 2011 for presumed CAWP were mailed a questionnaire. Primary endpoint was measured using the Treatment Efficacy Questionnaire (TEQ), consisting eight items (scored 1-5). Other outcome measures and the Somatic Symptom Checklist (SSC) score were also completed. Medical records were reviewed to ascertain patient, pain and TPI characteristics. The associations of TEQ score with clinical features and demographics were assessed using linear regression models. Results: Of the 218 patients contacted, 120 (55%) responded to the survey. Females, elderly, and married had greater odds of responding to the survey. Among the 120 patients, median pain duration was 12 months and right upper quadrant was the commonest site of pain (35%). Pain was rated as 8-10 (on a 1-10 scale) by 57%, 4-7 by 35% and 1-3 by 8% of patients. Majority (77%) described pain as an ache and 33% complained of a constant, daily pain. Narcotic use was reported in 46 (38%) and 88 (73%) had a history of at least one abdominal surgery. Most (94%) patients received a combination of anesthetic and corticosteroid for the TPI. The median (Interquartile range) TEQ score was 23 (18 to 30) with 44 of the 120 (37%) meeting the criteria for responder (successful TPI, TEQ ≥ 28). Compared to before treatment, 36% reported being “significantly better” and 22% “slightly better.” 37 of the 120 (30%) noted a response within 24 hrs of TPI, 23 (19%) in 1-3 days and 27 (22%) after three days and 35 (29%) never responded. Pain relief lasted >12 weeks in 43% of patients. The SSC score was univariately associated with TEQ score, but not age or BMI. Multiple linear regression analyses identified only SSC score as a significant negative predictor of the TEQ score (partial R-square of 5%, p<0.05) and the overall model R-square values were all <12%. Conclusion: Ultrasound guided TPI can provide significant, long-term symptom relief in a third of patients with chronic abdominal pain attributed to CAWP. Lower degree of somatization was modestly predictive of an increased response. CAWP should be considered in a patient with chronic abdominal pain and TPI should be offered, however, better predictors of response are needed.