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Microvascular Decompression for Classic Trigeminal Neuralgia: Determination of Minimum Clinically Important Difference in Pain Improvement for Patient Reported Outcomes

Reddy, Vishruth K. BA*; Parker, Scott L. MD*; Patrawala, Samit A. MD*; Lockney, Dennis T. BS*; Su, Pei-Fang PhD; Mericle, Robert A. MD§

doi: 10.1227/NEU.0b013e318286fad2
Research-Human-Clinical Studies

BACKGROUND: Outcomes studies use patient-reported outcome (PRO) measurements to assess treatment effectiveness, but can lack direct clinical meaning. Minimum clinically important difference (MCID) calculation provides a point estimate of the critical threshold needed to achieve clinically relevant treatment effectiveness. MCID remains uninvestigated for microvascular decompression (MVD), a common surgical procedure for trigeminal neuralgia.

OBJECTIVE: We aimed to determine MCID for the most commonly used PRO measures of pain after MVD: Visual Analog Scale (VAS) and Barrow Neurological Institute Pain Scale (BNI-PS).

METHODS: Sixty consecutive patients with classic trigeminal neuralgia who decided to undergo MVD by a single surgeon were prospectively assessed with VAS and BNI-PS preoperatively and 2 years postoperatively. Three anchors were used to assign each patient's outcome. We then used 3 well-established, anchor-based methods to calculate MCID.

RESULTS: Patients experienced significant improvement in both VAS (9.9 vs 2.0, P < .001) and BNI-PS (5.0 vs 1.9, P < .001) after MVD. The area under the receiver-operating characteristic curve was greater for BNI-PS than for VAS for all 3 anchors, indicating that BNI-PS is probably better suited for calculating MCID. The 3 MCID calculation methods generated a range of MCID values for each of the PROs (VAS: 1.40-8.87, BNI-PS: 0.95-3.26).

CONCLUSION: MVD-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 6.25 and for BNI-PS is 2.44.

ABBREVIATIONS: AUC, area under the receiver-operating characteristic curve

BNI-PS, Barrow Neurological Institute Pain Scale

CI, confidence interval

HTI, Health Transition Index

MCID, minimum clinically important difference

MDC, minimum detectable change

MVD, microvascular decompression

PRO, patient-reported outcome

SD, standard deviation

TN, trigeminal neuralgia

VAS, Visual Analog Scale

*Vanderbilt University Medical Center, Nashville, Tennessee;

Department of Biostatistics, Vanderbilt University Medical Center, Nashville, Tennessee;

§HW Neurological Institute, Nashville, Tennessee

Correspondence: Robert A. Mericle, MD, Department of Neurosurgery, HW Neurological Institute, 2011 Church Street, Suite 505, Nashville, TN 37203. E-mail: Mericle@HWneuro.com

Received February 29, 2012

Accepted December 25, 2012

Copyright © by the Congress of Neurological Surgeons