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Accurately Measuring Outcomes After Surgery for Adult Chiari I Malformation: Determining the Most Valid and Responsive Instruments

Godil, Saniya S. MD; Parker, Scott L. MD; Zuckerman, Scott L. BS; Mendenhall, Stephen K. BS; McGirt, Matthew J. MD

doi: 10.1227/NEU.0b013e3182897341
Research-Human-Clinical Studies

BACKGROUND: There has been a transition to using patient-reported outcome instruments (PROi) to assess surgical effectiveness. However, none of these instruments have been validated for outcomes of adult Chiari I malformation (CMI).

OBJECTIVE: The aim of this study was to determine the relative validity and responsiveness of various PROi in measuring outcomes after surgery for CMI.

METHODS: Fifty patients undergoing suboccipital craniotomy for adult CMI were prospectively followed for 1 year. Baseline and 1-year patient-reported outcomes (visual analog scale for head pain and visual analog scale for neck pain, Neck Disability Index [NDI], Headache Disability Index, SF-12, Zung Self-Rating Depression Scale, and EuroQol-5D [EQ-5D]) were assessed. A level of improvement in general health after surgery was defined as meaningful improvement. Receiver-operating characteristic curves were generated to assess the validity of PROi to discriminate between meaningful improvement and not. The difference between standardized response means (SRMs) in patients reporting meaningful improvement vs not as calculated to determine the relative responsiveness of each outcome instrument.

RESULTS: For pain and disability, the NDI was the most accurate discriminator of meaningful effectiveness (area under the curve: 0.90) and also most responsive to postoperative improvement (standardized response means difference: 1.87). For general health and quality of life, the SF-12 PCS, EQ-5D, and Zung Self-Rating Depression Scale were all accurate discriminators; however, SF-12 Physical Component Scale (SF-12 PCS) and EQ-5D were most accurate. SF-12 PCS was also most responsive.

CONCLUSION: For pain and disability, NDI is the most valid and responsive measure of improvement after surgery for CMI. For health-related quality of life, SF-12 PCS and EQ-5D are the most valid and responsive measures. NDI with SF-12 or EQ-5D is the most valid in patients with CMI and should be considered in cost-effectiveness studies.

ABBREVIATIONS: AUC, area under the curve

CMI, Chiari I malformation

EQ-5D, EuroQol-5D

HDI, Headache Disability Index

NDI, Neck Disability Index

QoL, quality of life

ROC, receiver-operating characteristic

SF-12 PCS, SF-12 Physical Component Scale

SRMs, standardized response means

VAS-Head, visual analog scale for headache

VAS-Neck, visual analog scale for neck pain

Zung, Zung Self-Rating Depression Scale

Department of Neurosurgery, Spinal Column Surgical Outcomes and Quality Research Laboratory, Vanderbilt University, Nashville, Tennessee

Correspondence: Matthew J. McGirt, MD, 4347 Village at Vanderbilt, Nashville, TN 37232-8618. E-mail:

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Received March 30, 2012

Accepted January 9, 2013

Copyright © by the Congress of Neurological Surgeons