Introduction: Outcomes studies utilize patient reported outcome (PRO) measurements to assess treatment effectiveness but can lack direct clinical meaning. Minimum clinical important difference (MCID) is a tool which measures the critical threshold needed to achieve clinically- relevant treatment effectiveness. MCID remains uninvestigated for Percutaneous Stereotactic Rhizotomy (PSR), a common surgical procedure for Trigeminal Neuralgia (TN). We aimed to determine MCID for the most commonly used PRO measures of pain after PSR: Visual Analog Scale (VAS) and Barrow Neurological Institute Pain Scale (BNI-PS).

Methods: 43 consecutive patients with TN who decided to undergo PSR by a single surgeon were prospectively assessed with VAS and BNI-PS preoperatively and 2 years postoperatively. Three anchors were utilized to assign each patient’s outcome. Three well-established, anchor-based methods were then used to calculate MCID.

Results: Patients experienced significant improvement in both VAS (10.0 vs. 3.35, p<0.001) and BNI-PS (5.0 vs. 2.44, p<0.001) after PSR. The area under the receiver operating characteristic curve was greater for BNI-PS compared to VAS for all three anchors, indicating BNI-PS is probably better-suited for calculating MCID. The three MCID calculation methods generated a range of MCID values for each of the PROs (VAS: 4.13-8.20, BNI-PS: 1.03-3.30).

Conclusions: PSR-specific MCID is highly variable based on calculation technique. Some of these calculations appear to either overestimate or underestimate the patients’ preoperative expectations. When the different MCID methods are averaged, the results are clinically appropriate and consistent with preoperative expectations. The average MCID for VAS is 5.98 and for BNI-PS is 2.29.

Patient Care: Understanding the Minimum Clinically Important Difference (MCID) of the standardized patient reported outcome (PRO) measurements for Trigeminal Neuralgia allows us to assign clinical meaningfulness to these standardized objective outcome tools.

Learning Objectives: By the conclusion of this session, participants should be able to: 1. Describe two standardized Patient Reported Outcome (PRO) measurement tools for patients undergoing PSR for TN. 2. Describe Minimum Clinically Important Difference (MCID) for TN patients undergoing PSR. 3. Describe the usefulness of "anchors" in calculating the MCID for TN patients undergoing PSR.

References: 1. Carreon LY, Glassman SD, Campbell MJ, Anderson PA: Neck Disability Index, short form-36 physical component summary, and pain scales for neck and arm pain: the minimum clinically important difference and substantial clinical benefit after cervical spine fusion. Spine J 10:469-474, 2010 2. Copay AG, Glassman SD, Subach BR, Berven S, Schuler TC, Carreon LY: Minimum clinically important difference in lumbar spine surgery patients: a choice of methods using the Oswestry Disability Index, Medical Outcomes Study questionnaire Short Form 36, and pain scales. Spine J 8:968-974, 2008 3. Copay AG, Subach BR, Glassman SD, Polly DW, Jr., Schuler TC: Understanding the minimum clinically important difference: a review of concepts and methods. Spine J 7:541-546, 2007 4. Eller JL, Raslan AM, Burchiel KJ: Trigeminal neuralgia: definition and classification. Neurosurg Focus 18:E3, 2005 5. Jaeschke R, Singer J, Guyatt GH: Measurement of health status. Ascertaining the minimal clinically important difference. Control Clin Trials 10:407-415, 1989 6. Lefaucheur JP, Drouot X, Cunin P, Bruckert R, Lepetit H, Creange A, et al: Motor cortex stimulation for the treatment of refractory peripheral neuropathic pain. Brain : a journal of neurology 132:1463-1471, 2009 7. Park SH, Hwang SK: Outcomes of gamma knife radiosurgery for trigeminal neuralgia after a minimum 3-year follow-up. Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia, 2011 8. Parker SL, Adogwa O, Paul AR, Anderson WN, Aaronson O, Cheng JS, et al: Utility of minimum clinically important difference in assessing pain, disability, and health state after transforaminal lumbar interbody fusion for degenerative lumbar spondylolisthesis. Journal of neurosurgery. Spine, 2011 9. Rogers CL, Shetter AG, Fiedler JA, Smith KA, Han PP, Speiser BL: Gamma knife radiosurgery for trigeminal neuralgia: the initial experience of The Barrow Neurological Institute. International journal of radiation oncology, biology, physics 47:1013-1019, 2000 10. Stratford PW, Binkley JM, Riddle DL, Guyatt GH: Sensitivity to change of the Roland-Morris Back Pain Questionnaire: part 1. Physical therapy 78:1186-1196, 1998 11. Tang CT, Chang SD, Tseng KY, Liu MY, Ju DT: CyberKnife stereotactic radiosurgical rhizotomy for refractory trigeminal neuralgia. J Clin Neurosci 18:1449-1453, 2011