International development of the patient-reported outcome indices for multiple sclerosis (PRIMUS)

The Patient-Reported Indices for Multiple Sclerosis (PRIMUS) comprises a suite of three scales for assessing symptoms, activity limitations, and quality of life in multiple sclerosis (MS). It was developed in the UK and has been shown to have excellent psychometric properties. This study describes the adaptation of eight language versions for Canadian English, Canadian French, French, German, Italian, Spanish, Swedish, and US English.

The PRIMUS was translated using the dual-panel process. Cognitive debriefing interviews conducted with MS patients assessed face and content validity. Psychometric and scaling properties were assessed via a two-administration postal survey conducted in each country involving the PRIMUS, the Nottingham Health Profile (NHP), the Unidimensional Fatigue Impact Scale (U-FIS), and demographic questions.

Cognitive debriefing interviews demonstrated the acceptability of the new language versions. Analysis of survey data showed that the new language versions of the three PRIMUS scales were unidimensional (as indicated by fit to the Rasch model) and that they had good internal consistency and reproducibility. PRIMUS scale scores correlated as expected with those on the NHP and the U-FIS. The scales in all countries were able to discriminate between groups of patients on the basis of their self-reported MS severity, general health, and employment status.

The PRIMUS was successfully adapted into eight new languages. Most of the tests showed the PRIMUS to have good unidimensionality and to have good internal consistency, reproducibility, and construct validity. The measure is now available for use in clinical studies and trials involving these countries and the UK. Further work is required to assess the measure's responsiveness.