Evaluating the psychometric properties of the Widespread Pain Index and the Symptom Severity scale in youth with painful conditions.

Background: Assessing features of centralized pain may prove to be clinically meaningful in pediatric populations. However, we are currently limited by the lack of validated pediatric measures.

Aim: We examined the psychometric properties of the Widespread Pain Index (WPI) and Symptom Severity (SS) scale, to assess features of centralized pain, in youth with painful conditions from three clinical samples: (1) musculoskeletal surgery, (2) headache, and (3) chronic pain.

Methods: Participants were 240 youth aged 10-18 years (Mage=14.8, SD=1.9) who completed the WPI and SS scale. Subsets of participants also completed additional measures of pain region, pain intensity, quality of life, pain interference and physical function.

Results: Increased features of centralized pain by age were seen for the WPI (=0.27, <0.01) and SS scale (=0.29, <0.01). Expected differences in sex were seen for the WPI (sex:t=-3.62, <0.01), but not the SS scale (sex:t=-1.73, =0.09). Reliability for the SS scale was adequate (α=.70). Construct validity was demonstrated through relationships between the WPI and pain regions (=.57, <0.01), and between the SS scale and quality of life (=-.59, <0.01) and pain interference (=.56, <0.01). Criterion validity was demonstrated by differences on the WPI between the surgery sample and the headache and chronic pain samples (F=17.55, <0.001). Comprehension of the SS scale items was problematic for some youth.

Conclusions: The WPI showed adequate psychometric properties in youth; however the SS scale may need to be modified. Our findings support the need to develop psychometrically sound instruments for comprehensive assessment of pain in pediatric samples.