Background: The chronic and treatment-resistant nature of nail psoriasis affects patients' lives not only physically but also psychologically. Although there are scoring systems available for disease severity, there is as yet no scale to evaluate the impact of this condition upon the patients' quality of life.
Objectives: This study aims to develop and validate a quality of life scale specifically for nail psoriasis.
Methods: A questionnaire was developed during a study conducted in France between 2004 and 2005. With the cooperation of l'Association Pour la Lutte Contre le Psoriasis, the questionnaire was sent to a random sample of 4000 of its 17,000 members.
Results: The response rate was 33%. Of the 1309 questionnaires returned, 795 showed the presence of nail psoriasis and these were eligible. The scale score is obtained by adding together the responses to the 10 questionnaire items and the result is expressed as a percentage. The value of the score obtained is proportional to the functional difficulty experienced. The determination of Cronbach's a coefficient and a Principal Component Factor Analysis show, respectively, very good internal consistency and the unidimensional nature of the scale. Test-retest results on 15 patients showed good reproducibility. Results were validated with reference to the Dermatology Life Quality Index. In this study, the NPQ10 score is significantly influenced by gender (women have a higher score) and by the duration of psoriasis (recent onset implies greater functional difficulty). Finally, the score is much higher when the nail psoriasis affects both the hands and the feet.
Conclusion: This study confirms a change in the quality of life of patients who have nail psoriasis. The NPQ10 scale, specific to this condition, is simple to use and has the attributes needed in a quality of life scale. The scale must now be tested in longitudinal studies (such as clinical trials) to confirm its ability to measure a change in status.