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