Objective: To develop and assess the reliability and construct validity of a scale assessing disability involving the mouth in systemic sclerosis (SSc).
Methods: We generated a 34-item provisional scale from mailed responses of patients (n = 74), expert consensus (n = 10) and literature analysis. A total of 71 other SSc patients were recruited. The test-retest reliability was assessed using the intraclass coefficient correlation and divergent validity using the Spearman correlation coefficient. Factor analysis followed by varimax rotation was performed to assess the factorial structure of the scale.
Results: The item reduction process retained 12 items with 5 levels of answers (total score range 0-48). The mean total score of the scale was 20.3 (SD 9.7). The test-retest reliability was 0.96. Divergent validity was confirmed for global disability (Health Assessment Questionnaire (HAQ), r = 0.33), hand function (Cochin Hand Function Scale, r = 0.37), inter-incisor distance (r = -0.34), handicap (McMaster-Toronto Arthritis questionnaire (MACTAR), r = 0.24), depression (Hospital Anxiety and Depression (HAD); HADd, r = 0.26) and anxiety (HADa, r = 0.17). Factor analysis extracted 3 factors with eigenvalues of 4.26, 1.76 and 1.47, explaining 63% of the variance. These 3 factors could be clinically characterised. The first factor (5 items) represents handicap induced by the reduction in mouth opening, the second (5 items) handicap induced by sicca syndrome and the third (2 items) aesthetic concerns.
Conclusion: We propose a new scale, the Mouth Handicap in Systemic Sclerosis (MHISS) scale, which has excellent reliability and good construct validity, and assesses specifically disability involving the mouth in patients with SSc.