Validation of the individualised neuromuscular quality of life for the USA with comparison of the impact of muscle disease on those living in USA versus UK

BACKGROUND: The Individualised Neuromuscular Quality of Life (INQoL) questionnaire is a published muscle disease specific measure of QoL that has been validated using both qualitative and quantitative methods in a United Kingdom population of adults with muscle disease. If INQoL is to be used in other countries it needs to be linguistically and culturally validated for those countries. It may be important to understand any cultural differences in how patients rate their QoL when applying QoL measures in multi-national clinical trials. METHODS: We conducted a postal survey of QoL issues in US adults with muscle disease using an agreed translation, from UK to US English, of the same questionnaire as was used in the original construction of INQoL. This questionnaire included an opportunity for free text comments on any aspects of QoL that might not have been covered by the questionnaire. We examined the responses using both quantitative and qualitative approaches. The frequency of the responses in US versus UK populations was compared using appropriate correlation tests and Rasch analysis. A phenomenological approach was used to guide the qualitative analysis and facilitate the exploration of patients' perceptions and experiences. RESULTS: The US survey received 333 responses which were compared with 251 UK survey responses. We found that INQoL domains covered all the issues raised by US subjects with no additional domains required. The experiences of those with muscle disease were remarkably similar in the US and UK but there were differences related to the impact of muscle disease on relationships and on employment which was greater for those living in the United States. The greater impact on employment was associated with a higher importance rating given to employment in the US. This may reflect the lower level of financial support for those who are unemployed, and the loss of employment related health benefits. CONCLUSIONS: INQoL is appropriate for use in US population but there may be differences in the importance that US subject attach to certain aspects of QoL that could be the basis for further study. If these differences are confirmed then this may have implications for the interpretation of QoL outcomes in multi-national trials.