Validation of the Headache Impact Test (HIT-6) in patients with chronic migraine

Regina Rendas-Baum 0 Min Yang 0 Sepideh F Varon 2 Lisa M Bloudek 1 Ronald E DeGryse 2 Mark Kosinski 0 0 QualityMetric Incorporated , 24 Albion Road, Bldg 400, Lincoln, RI 02865-4207 , USA 1 Xcenda, LLC. , 4114 Woodlands Pkwy, Palm Harbor, FL 34685 , USA 2 Allergan, Inc. , 2525 Dupont Drive, Irvine, CA 92612 , USA Background: The Headache Impact Test (HIT)-6 was developed and has been validated in patients with various types of headache. The objective of this study was to report the psychometric properties of the HIT-6 among patients with chronic migraine. Methods: Data came from two international, multicenter, randomized, double-blind, placebo-controlled clinical trials of chronic migraine patients (N = 1,384) undergoing prophylaxis therapy. Confirmatory factor analysis and differential item functioning (DIF) analysis were used to test the latent structure and cross-cultural comparability of the HIT-6. Reliability, construct validity, and responsiveness were assessed. Two sets of criterion groups were used: (1) 28-day headache frequency: <10, 10-14, and 15 days; (2) sample quartiles of the total cumulative hours of headache: <140, 140 to <280, 280 to <420, and 420 hours. Two sets of responsiveness categories were defined as reduction of <30%, 30% to <50%, or 50% in (1) number of headache days and (2) cumulative hours of headache. Results: Measurement invariance tests supported the stability of the HIT-6 latent structure across studies. DIF analysis supported cross-cultural comparability. Good reliability was observed across studies (Cronbach's : 0.75-0.92; intraclass correlation coefficient: 0.76-0.80). HIT-6 scores correlated strongly (0.86 to 0.59) with scores of the Migraine-Specific Quality-of-Life Questionnaire. Analysis of variance indicated that HIT-6 scores discriminated across both types of criterion groups (P<0.001), across studies and time points. HIT-6 change scores were significantly higher in magnitude in groups experiencing greater improvement (P<0.001). Conclusion: All measurement properties were consistently verified across the two studies, supporting the validity of the HIT-6 among chronic migraine patients. Trial registration: NCT00156910 and NCT00168428 on www.ClinicalTrials.gov. - Background Migraine is recognized as a major cause of disability, adversely affecting the daily functioning of an estimated 12% of the US population [1,2]. For some patients, the frequency of migraine attacks increases over time and progresses to high-frequency episodic migraine (1014 days per month) or chronic migraine (15 days per month) [3]. Patients with episodic migraine (<15 days per month) are estimated to transition into chronic migraine at a rate of about 2.5% per year [4]. Increases in the frequency of headache leading to chronic migraine are known to be accompanied by anatomical and functional changes [5]. Understanding the impact of these changes helps define the characteristics of chronic migraine patients and how they differ from those of patients with lower frequency migraine. Frequency of headaches is the key distinguishing feature used to classify migraine subtypes (e.g., low-frequency episodic migraine, high-frequency episodic migraine, and chronic migraine) [6]; however, researchers have become increasingly aware that the differential impact of migraine cannot be fully assessed through the exclusive use of such measures. This has led to the increasing use of diseasespecific patient-reported outcome (PRO) measures in migraine research and clinical practice [7]. The use of standardized PRO instruments has contributed greatly to a more accurate assessment of the impact of the disorder on patients health-related quality of life (HRQOL), and these measures are currently recommended by experts in the field [8,9]. Nevertheless, the integrity of PRObased evaluations rests on the availability of psychometric data endorsing its validity among the clinical population of interest. Several disease-specific measures of quality of life were developed and validated in samples of patients with headache. PRO instruments measuring headache impact are often used across different migraine subtypes, the assumption being that the instruments validity is retained across these clinical subgroups. However, evidence of an instruments properties among specific subtypes of migraine is often not available. The 6-item Headache Impact Test (HIT-6) is a brief tool for assessing the impact of headache in both clinical research and practice. The development and validation study indicated that the HIT-6 possessed good psychometric properties among headache sufferers [10]. Another study conducted among patients seeking headache-specialty care confirmed high indices of reliability, as well as construct and face validity [11]. Several important properties of the HIT-6 have been documented, including its between-group and within-group minimally important difference (MID) [12,13] and its ability to detect change in clinical measures of migraine patients [14]. Although strong evidence has been found supporting the validity of the HIT-6 in headache sufferers in general, a full evaluation of the HIT-6 psychometric properties specifically in a subgroup of headache patients with chronic migraine, a distinct headache disorder characterized by the International Classification of Headache Disorders Revised Criteria (ICHD-IIR) as 15 headache days per month for at least 3 months, with 8 days per month fulfilling criteria for migraine without aura, has not been conducted. The ability to detect significant change in clinical parameters [14,15] has been evaluated in samples of patients with chronic daily headache or chronic migraine, but a full psychometric evaluation, including longitudinal measurement invariance and differential item functioning, was not performed. Furthermore, none of the previous validation studies [10,11] were conducted using clinical trial samples. This is an important aspect of validity because PRO instruments are key elements in efficacy studies of migraine treatment. The current study used data from two independent clinical trials of chronic migraine patients to comprehensively evaluate the psychometric properties of the HIT-6 in chronic migraine patients. Methods Sample Data used in the analyses came from a total sample of 1,384 patients with chronic migraine who participated in 2 studies that evaluated onabotulinumtoxinA (BOTOX, Allergan, Inc.) as headache prophylaxis the Phase III REsearch Evaluating Migraine Prophylaxis Therapy with Botulinum Toxin Type A (PREEMPT) trials [16,17]. Both PREEMPT trials were multicenter, double-blind, randomized, and placebo-controlled. The total study period consisted of 60 weeks, which included a 4-week baseline phase capturing inclusion/exclusion information, followed by a 24-week double-blind treatment phase, and a final 32-week, open-label extension phase. The studies were conducted between January of 2006 and August of 2008 in the (...truncated)