Interpretation and validity of changes in scores on the Graves' ophthalmopathy quality of life questionnaire (GO-QOL) after different treatments

OBJECTIVE The Graves' ophthalmopathy quality of life questionnaire (GO-QOL) is the first instrument available to measure health-related quality of lif e (HRQL) of patients with Graves' ophthalmopathy. The main objective of thi s study was to define a minimal clinically important difference (MCID) in s care on the GO-QOL that can be considered an import;ant improvement in HRQL by examining changes in GO-QOL scores in patients who subjectively report improvement from their treatment. A secondary objective was to test the lon gitudinal validity of the GO-QOL, using prespecified hypotheses about expec ted treatment effects. DESIGN A prospective cohort study. PATIENTS We included 164 patients who were scheduled for radiotherapy (23), orbital decompression (10 for sight loss, 38 for exophthalmos), eye muscle surgery (31), eyelid lengthening (43) or blepharoplasty (19). MEASUREMENTS Patients completed the GO-QOL and three general HRQL questionn aires, before and three or six months after treatment, depending on the per formed procedure. Clinical characteristics were collected from the medical records. Mean changes in GO-QOL scores and effect sizes were calculated aft er different treatments, and in subgroups of responders and nonresponders a ccording to clinical characteristics and according to the patients themselv es. RESULTS A clinical response to treatment was associated with a change in GO -QOL scores of approximately 10-20 points after major treatments (radiother apy or decompression), and with a change of approximately 3-10 points after minor surgery (eye muscle surgery, eyelid lengthening, blepharoplasty). Ch anges in GO-QOL scores of about 6-10 points were considered important impro vements by the patients themselves. The direction and amount of change in G O-QOL scores after different treatments were in accordance with our prespec ified hypotheses about treatment effects. Effect sizes in the GO-QOL subsca les were generally higher than effect sizes of the general HRQL subscales, supporting the longitudinal validity of the GO-QOL. CONCLUSIONS As a general guideline, one could consider a mean change of at least 6 points on one or both subscales an important change in daily functi oning far patients. For more invasive therapies, a change of at least 10 po ints is recommended as a minimal clinically important difference.