The Multidimensional Symptom Index: A new patient-reported outcome for pain phenotyping, prognosis and treatment decisions.

BACKGROUND

There are few patient-reported outcomes routinely used that capture frequency and interference of different pain-related symptoms on a single scale. The purpose of this study was to describe the development and initial validation of the new Multidimensional Symptom Index (MSI).

METHODS

Items were generated from patient interviews of the experience of chronic pain. Health valuations were created from rankings of 82 healthy subjects for each of 120 symptom (×10) × frequency (×3) × interference (×4) combinations using preference-based health valuations (0-100). Ranks for each symptom combination were then used in scale scoring. A sample of 300 patients with acute or chronic pain subsequently completed the MSI and a battery of other tools. Exploratory (EFA) and Confirmatory (CFA) factor analyses were triangulated with theory to arrive at the factor structure. Convergent validity was tested against established measures.

RESULTS

Health rankings resulted in scores of 0-12 for each of the 10 symptom types. Factor analyses revealed two factors: MSI Somatic Symptoms and MSI Non-Somatic Symptoms. The MSI also quantified number of symptoms experienced (/10), mean frequency (/3) and mean interference (/4). The indices showed appropriate associations with the established PROs.

CONCLUSIONS

The MSI is a new symptom-focused PRO that allows patient phenotyping and may have value for screening, prognosis and evaluating change.

SIGNIFICANCE

This article presents the development and psychometric properties of a new measure of pain and related symptom frequency and interference. This measure could aid clinicians in establishing clinically relevant pain phenotypes for screening, prognosis and treatment decisions.