EVALUATION OF A MODIFIED BRIEF PAIN INVENTORY TO MEASURE PAIN ASSOCIATED WITH HERPES ZOSTER

*P. Coplan (1), K. Schmader (2), A. Nikas (1), I. Chan (1), P. Choo (3), H. Guess (1), M. Levin (4), G. Johnson (5), M. Oxman (6). (1) Merck Research Laboratories, West Point, PA, USA; (2) Duke University & Durham VA Medical Centers, Durham, NC, USA; (3) Harvard Pilgrim Health Care & Harvard Medical School, Boston, MA, USA; (4) University Of Colorado, Denver, CO, USA; (5) VA Cooperative Studies Program Coordinating Center, West Haven, CT, USA; (6) University of California San Diego & San Diego VA Medical Centers, La Jolla, CA, USA

Objectives:
(1) To assess the reliability and validity of the Zoster Brief Pain Inventory (ZBPI) in measuring zoster pain and (2) to evaluate the operational definition of postherpetic neuralgia (PHN) as a worst pain score (WPS) of > 3 on the ZBPI 0-10 scale (0= none, 10= worst imaginable pain) more than 30 days after rash onset.

Methods:
In a prospective observational study, outpatients > 60 years of age with zoster in Boston, Denver, Durham, and San Diego were interviewed at regular intervals until the earlier of 6 months or a WPS of 0 reported on two consecutive interviews. At each interview, patients completed in person or by telephone the ZBPI, McGill Pain Questionnaire present pain intensity (PPI) and modified PPI measuring pain in the last 24 hours (modified PI) scales from the McGill Pain Questionnaire, quality of life (QoL)
(SF-12 and EuroQOL) and activities of daily living (ADL) questionnaires. Days 14 and 35 after rash onset were pre-specified as primary timepoints. Kappa statistics compared WPS cut-offs with the six-point PPI and modified PI to evaluate the proposed operational definition of PHN.

Results:
121 subjects were enrolled (48% over 70 years, 63% female, 87% Caucasian) within 14 days of rash onset (48% within 7 days). The intra-class correlation coefficient of reliability was (=0.63 comparing WPS measures at Day 5-7 to Day 8-10 and 0.78 comparing Day 8-10 to Day 11-14. Spearman correlations between the ZBPI WPS and the PPI were 0.73 and 0.77 at Day 14 and Day 35 respectively. Correlations with interference with ADL ranged from between 0.52 with and Walking Ability to 0.77 with General Activity. Increasing WPS were associated with worsening QOL scores and increasing ADL interference scores. The Kappa statistic for definition of PHN of WPS
>3 compared to the McGill modified PI score ("moderate" or worse pain) was 0.67 (95% CI = 0.49 - 0.80) and a cut-off > 3 provided the optimal Kappa compared to the McGill modified PI score ("moderate" or worse pain). No significant interference in ADL was observed at WPS of < 3.

Conclusions:
The ZBPI is a reliable and valid measure of zoster pain. A WPS > 3 after 30 days since rash onset is a reasonable operational definition of PHN.

Corresponding Author: P. Coplan, Sc.D., Associate Director, Epidemiology Department, Merck Research Laboratories, Merck & Co., Inc., PO Box 4, BL 1-7, West Point, PA 19486-0004, USA