Real-World Effectiveness of Polymerized House-Dust-Mite Subcutaneous Immunotherapy up to 24 Months: Why Baseline Symptom Severity Shapes Measurement of the Combined Symptom-Medication Response.

Background/

Objectives

Allergic rhinoconjunctivitis (AR) induced by house dust mites (HDMs) is a common condition that impairs quality of life, and allergen immunotherapy is the only treatment accepted to modify its natural course. However, real-world evidence on polymerized HDM subcutaneous immunotherapy (SCIT) remains limited. We evaluated the up to 24-month effectiveness of polymerized HDM SCIT and examined how baseline symptom burden affects the measured response.

Methods

In a retrospective, single-arm, real-world cohort, 353 patients (mean age 15.9 (12.3) years) with HDM-induced AR with/without asthma (asthma subpopulation, n = 112) initiated polymerized SCIT (ALXOID®, Inmunotek S.L., Spain) with an extract of house dust mites (Dermatophagoides pteronyssinus, D. farinae, Blomia tropicalis). Patients were followed for up to 24 months; 139 contributed an observation at month 12 and 67 at month 24. The primary outcome was the Rhinoconjunctivitis Combined Symptom-Medication Score (RCSMS); secondary outcomes were a visual analog scale (VAS) and the ESPRINT-15 quality-of-life questionnaire. Effectiveness was estimated using mixed models for repeated measures. The pre-specified primary-analysis population was restricted to a baseline RCSMS ≥ 2 to avoid floor effects and regression to the mean at low baseline scores.

Results

At month 24, the RCSMS decreased by 0.938 points (-35.3%) in the full cohort and by 48.3% in the baseline RCSMS ≥ 2 population; in the full cohort, the VAS and ESPRINT-15 improved by 50.6% and 69.7%, respectively (all p < 0.001; within-subject effect sizes were small for the full-cohort RCSMS and medium for all other outcomes). The shape of the improvement trajectory did not differ by age group, and all age groups exceeded the minimal clinically important difference; the age analysis was exploratory. Patients with baseline RCSMS < 2 showed continued improvement in VAS and ESPRINT-15 scores. In contrast, the RCSMS increased, a pattern consistent with a statistical floor effect, suggesting limited responsiveness of the score at low baseline values.

Conclusions

Up to 24 months, polymerized HDM SCIT was associated with clinically meaningful improvements in symptoms, medication use, and quality of life, most clearly in patients with a baseline RCSMS ≥ 2. Baseline symptom severity should be considered when interpreting combined symptom-medication outcomes in allergen immunotherapy. The single-arm design precludes causal inference.