Clinical Meaning of Promis Pain Interference and Pain Behavior Measures for Children with Sickle Cell Disease

Introduction: The Patient Reported Outcomes Measurement Information System (PROMIS) includes tools to assess pain interference and pain behavior for pediatric patients. These domains are especially relevant for children with sickle cell disease who have recurring pain. Though these domains have been shown to be reliable and valid in this patient population, their adoption in practice is significantly limited by lack of clinical interpretation of the scores. The objective of this study was to add clinical meaning to the self-reported pain inference and pain behavior scores for children with sickle cell disease.

Methods: We recruited a convenience sample of children with sickle cell disease, 8-17 years of age at Children's Hospital of Wisconsin to complete PROMIS surveys. The pediatric PROMIS measures are scored on a T-score metric with a mean of 50 and standard deviation of 10, where 50 represents the mean of the pediatric sample in which the item response theory parameters for the measures were estimated. The PROMIS measures for pain interference and pain behavior use a Likert response scale and have a one week recall period. The Likert scale responses were characterized into three groups to support clinical interpretation of PROMIS scores. Patients who reported "never" or "almost never" for all items on the pain interference domain were considered to be having "no or minor pain". Patients who reported "often" or "almost always" for all items were considered to be having "substantial" pain. All other patients were classified as having "mixed" pain interference. Similarly, in the pain behavior domain, patients were categorized as having 'no or minor' (response to all items: "had no pain", "never", "almost never"), or 'substantial' (response to all items: "often" and "almost always") pain behavior, with remaining considered as having mixed pain behavior. For the domains of pain interference and pain behavior, higher scores mean more impairment. The range of scores for patients with no or minor, mixed and substantial problems on the measures were used to determine the clinical thresholds to identify those with mild, moderate and severe symptoms. The thresholds were validated by comparing the distribution of patients who needed to take pain medications in the past 7 days among the groups of patients with mild, moderate and severe symptoms, using Chi-square tests and adjusting for multiple pairwise comparisons.

Results: Our study included 115 eligible children (mean (sd) age = 11.8 (2.8) years), of which 54% were females and 95% were African Americans. For pain interference, there were 36 patients reporting no or minor issues, 16 had substantial issues and the remaining 62 were considered to have mixed pain interference (T-score was missing for one patient). Based on the T-score ranges of these groups, the clinical thresholds of mild and severe pain interference were set to be ≤ 48.3 and ≥ 63.6 respectively. For the domain of pain behavior, 30 children reported having no or minor problems, 6 had substantial problems and the remaining 79 endorsed mixed responses on the items. The range-based thresholds for mild and severe pain behavior were similar at ≤ 41.3 and ≥ 57.3 respectively. Figure 1 shows an example of the distribution of item-level response for one item within the severity groups. There were significant differences in the proportion of patients needing to take pain medications at home in the prior 7 days among those with mild, moderate and severe pain interference (% patients needing pain medications, Mild= 7%; Moderate = 28%; Severe = 44%; p = 0.0095) and pain behavior (% patients needing pain medications, Mild= 6%; Moderate = 32%; Severe = 30%; p = 0.0013). The pairwise comparisons indicate that there were significant differences in proportion of patients needing pain medications between the mild and the moderate/severe groups. However, there were no significant differences in pain medication use between the moderate and severe patients.

Conclusions: We show that T-scores ≤ 48.3 and ≤ 41.3 on the respective pain interference and pain behavior domains serve as thresholds for children with no or only mild pain. Whereas children with severe pain have T-scores ≥ 63.6 and ≥ 57.3 on pain interference and pain behavior domains respectively. This facilitates the clinical interpretation of PROMIS pain interference and pain behavior scores for children with sickle cell disease.

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