Determination of the minimally important difference in a nasal symptom score in house dust mite allergy

Background House dust mite (HDM) allergens are responsible for the most prevalent persistent respiratory allergies. Clinical trials in this field often use a four‐component nasal symptom score (T4NSS) as a measure of efficacy. Methods The present observational, prospective, multinational, multicenter study determined the minimal important difference (MID) for a T4NSS in children, adolescents, and adults with physician‐diagnosed HDM‐induced allergic rhinoconjunctivitis (AR). Patients rated the T4NSS daily, a 15‐point global rating of change scale (GRCS) and the Rhinoconjunctivitis Quality of Life Questionnaire weekly. The MID was determined primarily by using a regression method with a GRCS threshold of 2. Results A total of 546 patients (210 adults, 133 adolescents, and 203 children) were included; 92.6% of the patients had moderate‐to‐severe AR, and 30.1% had concomitant mild asthma. During the first week, the mean ± standard deviation T4NSS was 5.68 ± 2.76 in adults, 5.34 ± 2.66 in adolescents, and 5.07 ± 2.48 in children. In a GRCS regression analysis, the MID [95% confidence interval] for the T4NSS was −0.90 [−1.06;‐0.75] overall (n = 509), −0.94 [−1.19;‐0.69] in children (n = 187), −0.74 [−1.07;‐0.41] in adolescents (n = 125), and −1.04 [−1.29;‐0.79] in adults (n = 197). The MID did not differ greatly from one disease severity tertile to another. Confirmatory distribution‐based analyses yielded overall MID values of −0.87 for the first week of the study and −0.93 for the week 2–week 1 difference. Conclusion The MID for improvement in the T4NSS is at least −0.90 units in children, adolescents, and adults suffering from HDM‐induced AR This value could be rounded up to −1 unit for convenience.