Using a self-reported functional score to assess disease progression in systemic sclerosis

Objectives. This study compares the scleroderma Functional Score (FS) with the validated Disability Index of the Health Assessment Questionnaire (HAQ-DI) and other outcome measures. The aim is to determine if the FS is useful as an objective assessment tool for longitudinal evaluation of the functional impact of systemic sclerosis (SSc).Methods. A cohort of 135 patients was studied (M:F, 15:120), with a mean age of 45.7 (s.d. = 13.2) at SSc disease onset. 69 (51%) had diffuse cutaneous scleroderma (dcSSc) and 66 (49%) had limited disease (lcSSc). The mean interval between the two assessments was 1.8 yrs (s.d. = 1.2). Functional impact was determined by evaluating archived self-reported questionnaires (FS, HAQ and scleroderma-VAS). Concurrent evaluation of the disease severity score was derived from clinical data stored in the hospital database and from medical case note reviews.Results. At baseline, the mean FS was 11.0 (s.d. = 9.0) and at reassessment 12.0 (s.d. = 9.2). The mean absolute change in FS between the two assessments was 4.1 (s.d. = 4.9). With time 49% (n = 66) showed a clinically significant change in their functional ability with regard to FS, of these 29% (n = 39) worsened and 20% (n = 27) improved. There was an excellent cross-sectional correlation between the FS and the HAQ-DI (ρ = 0.90; P < 0.0001). Also, a strong correlation between longitudinal change in these two outcome measures (ρ = 0.59, P < 0.0001) was observed.Conclusions. This is the first longitudinal study of the scleroderma FS. It demonstrates that the FS can capture bidirectional and clinically significant changes in SSc related disability over time. The concurrent validity of the FS is asserted through its strong correlation with the HAQ-DI. The FS is a disease-specific, inexpensive and practical instrument for assessing functional status in SSc. It is a promising self-administered assessment tool for use in evaluating new SSc treatments.