THE VALIDITY OF A MEASURE OF THE SEVERITY AND DURATION OF HERPES ZOSTER PAIN

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

Objectives:
A zoster pain measure that incorporates severity and duration is potentially useful as an outcome measure in zoster clinical trials. This study assessed the validity and responsiveness of a zoster pain severity-by-duration measure using an area under the curve (AUC) of the 0-10 worst pain scale (0= none, 10= worst imaginable pain) from the Zoster Brief Pain Inventory (ZBPI).

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 over 6 months or until no zoster pain was reported on 2 consecutive interviews. The following questionnaires were administered in person or by telephone: the ZBPI, McGill Pain Questionnaire (MPQ), SF-12, EuroQoL, and a zoster-specific activities of daily living (ADL) questionnaire. AUCs for these measures were calculated by multiplying the average of two consecutive scores by the duration (days) between those scores. Construct validity was assessed by Spearman correlations and trends between the ZBPI pain AUC and AUCs of other measures. Responsiveness was assessed by the proportional change in the pain AUC associated with changes in the other AUC measures of pain, function and quality of life.

Results:
121 subjects were enrolled (48% over 70 years, 63% female, 87% Caucasian, 38% high school education or less) within 14 days of rash onset (48% within 7 days). The ZBPI Pain AUC correlated highly with the MPQ pain AUC (0.89, 95% CI=0.85-0.93), the SF-12 pain domain (0.84, 95% CI=0.78-0.89), EuroQoL quality of life AUC (0.82), and ADL interference AUCs (0.54-0.88 for 19 activities). Increasing pain AUC was associated with increasing ADL interference at days 14, 35 and 70 after rash onset. A 60% reduction in ZBPI pain AUC was associated with a 56% reduction in MPQ AUC, a 52% reduction in SF-12 pain domain AUC, and reductions in ADL interference AUCs ranging from 53-73%.

Conclusions:
The ZBPI severity-by-duration pain measure (AUC) is a valid measure of zoster pain severity and duration that was highly correlated with other pain measures, quality of life and ADL interference and was responsive to changes in zoster pain severity.

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