Minimal clinically important difference in the fibromyalgia impact questionnaire.
OBJECTIVE
The Fibromyalgia Impact Questionnaire (FIQ) is a disease-specific composite instrument that measures the effect of problems experienced by patients with fibromyalgia (FM). Utilization of the FIQ in measuring changes due to interventions in FM requires derivation of a clinically meaningful change for that instrument. Analyses were conducted to estimate the minimal clinically important difference (MCID), and to propose FIQ severity categories.


METHODS
Data from 3 similarly designed, 3-month placebo-controlled, clinical treatment trials of pregabalin 300, 450, and 600 mg/day in patients with FM were modeled to estimate the change in the mean FIQ total and stiffness items corresponding to each category on the Patient Global Impression of Change. FIQ severity categories were modeled and determined using established pain severity cutpoints as an anchor.


RESULTS
A total of 2228 patients, mean age 49 years, 93% women, with a mean baseline FIQ total score of 62 were treated in the 3 studies. Estimated MCID on a given measure were similar across the studies. In a pooled analysis the estimated MCID (95% confidence interval) was 14% (13; 15) and for FIQ stiffness it was 13% (12; 14). In the severity analysis a FIQ total score from 0 to <39 was found to represent a mild effect, >or= 39 to <59 a moderate effect, and >or=59 to 100 a severe effect.


CONCLUSIONS
The analysis indicates that a 14% change in the FIQ total score is clinically relevant, and results of these analyses should enhance the clinical utility of the FIQ in research and practice.
Oregon Health and Science University, Portland, OR, USA.
Robert M
RM
Bennett
Andrew G
AG
Bushmakin
Joseph C
JC
Cappelleri
Gergana
G
Zlateva
Alesia B
AB
Sadosky
D000700:Analgesics / Q000627:therapeutic use; D004185:Disability Evaluation; D005260:Female; D005356:Fibromyalgia / Q000150:complications / Q000188:drug therapy / Q000503:physiopathology*; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000188:drug therapy / Q000209:etiology / Q000503:physiopathology; D000069583:Pregabalin; D016032:Randomized Controlled Trials as Topic; D012720:Severity of Illness Index; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives / Q000627:therapeutic use
D000700:Analgesics; D000069583:Pregabalin; D005680:gamma-Aminobutyric Acid