Validation of the Symptomatic Dermographism Quality of Life Questionnaire (SD-QoL)

Background: Symptomatic dermographism (SD) is the most common subtype of chronic inducible urticaria. It is characterized by the recurrent appearance of itch and subsequent strip-shaped wheals induced by applying shear forces on the skin, such as stroking or rubbing. The impossibility to avoid symptom's occurrence in most cases leads to a marked quality-of-life (QoL) impairment. As of yet, a validated and disease-specific instrument to adequately assess QoL in patients with SD is not available. Objective: To validate the first disease-specific patient-reported outcome measure to assess health-related QoL impairment in patients with SD, the Symptomatic Dermographism Quality-of-Life Questionnaire (SD-QoL). Methods: A 13-item QoL questionnaire had been previously generated and published. Now, the SD-QoL was analyzed regarding its domain structure and tested for its reliability and validity by evaluating its internal consistency, test-retest reliability, and convergent and known-groups validity. Results: In total, 106 patients with SD participated in the SD-QoL validation study. The results suggest a 3-domain structure (“symptoms,” “functioning,” and “emotions”/“appearance”) with an excellent internal consistency of the domains as well as the overall instrument. Furthermore, the analyses indicated high levels of convergent validity and known-groups validity as well as an excellent test-retest reliability. Conclusions: The SD-QoL is the first validated disease-specific QoL instrument for SD that allows assessing QoL of patients with SD in clinical trials as well as in routine patient care.