The minimally important difference (MID) for patient-reported outcomes including pain, fatigue, sleep and the Health Assessment Questionnaire Disability Index (HAQ-DI) in primary Sjogren's syndrome

Objectives We wanted to determine the MID for the HAQ, pain, fatigue sleep and global VAS (0-100mm) in Sjogren's syndrome (SS) using a patient-reported overall health status anchor. Methods Patients with a diagnosis of primary Sjogren's syndrome (pSS) who had answered a standardised questionnaire at two consecutive visits including an overall health status question: "How would you describe your overall status since your last visit: much better, better, the same, worse, much worse?" were included. The MID was calculated as the mean change between visits for those who rated their disease as better or worse. Scales on VAS were from 0 (best) to 100 (worst). Results Forty patients met the inclusion criteria (97% female, mean age 58 years, mean disease duration 10 years). The mean baseline HAQ was 0.68. Ten rated their status as better and 14 as worse than the previous visit. MID estimates for improvement 1 worsening (SD) respectively were: -7.4 (27.8) / 20.7 (20.0) for pain VAS, -6.2 (28.3) / 15.2 (21.8) for fatigue VAS, -24.0 (24.0) / 15.2 (28.0) for sleep VAS, -0.18 (0.23) / 0.14 (0.30) for HAQ and -23.1 (21.6) / 16.4 (20.9) for global VAS. Spearman's rho correlation coefficients for the patient-reported outcomes were 0.38 (pain VAS), 0.54 (fatigue VAS), 0.55 (sleep VAS), 0.39 (HAQ), and 0.57 (global VAS), p<0.05. Conclusion The MID for pain and fatigue are greater for worsening than improvement. A small change in the HAQ is detected as a change in status by the patient. This knowledge may aid those who treat SS and in designing intervention studies.