Allergy is peculiar in that the burden of disease varies considerably between times of exposure versus nonexposure to allergens. The quality of life of patients with allergy deteriorates during exposure to the relevant allergen; however, immunotherapy diminishes the reduction and thereby improves quality of life for these patients.
There is no consensus on how patient-reported outcomes should be calculated and there is no validated standard for reporting health impact for allergy immunotherapy. Most often used is the disease-specific Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ) developed to assess seven domains of the quality of life in symptomatic patients during allergen exposure (e.g., during a pollen season), allowing for assessment of a symptomatic baseline. A minimal important difference for change in the actively treated group of 0.5 has been proposed based on studies of pharmacotherapy; however, in clinical trials of seasonal allergen immunotherapy, subjects are typically randomized during a preseasonal, relatively asymptomatic period, and results reflect the difference between groups treated with active treatment versus placebo. Evaluating symptoms in a previous season will not lead to valid baseline values, because symptoms are dependent on exposure, which varies from year to year; however, baseline assessment might be relevant for perennial allergies, such as allergy to house dust mites. A minimal important difference appropriate to the design of clinical trials of allergy immunotherapy, without a symptomatic baseline and comparing treatment groups rather than change from baseline, has not yet been established.
Three large trials of sublingual allergy immunotherapy tablets demonstrated a statistically significant improvement in quality of life among patients with grass pollen allergic rhinoconjunctivitis during the pollen season. All studies used the disease-specific RQLQ instrument. In the long-term trial with the SQ grass sublingual allergy immunotherapy tablet, the highest effects were observed in the sleep and eye symptom domains. Impaired sleep exerts a particular effect on patients' well-being, as well as school and work performance, and, therefore, has a major impact on quality of life. The beneficial effect of immunotherapy was sustained for two years after the end of treatment. A large study also demonstrated significant improvement in quality of life using subcutaneous injection immunotherapy. All domain scores improved significantly using the RQLQ instrument.
Larsen J N et al. Allergy immunotherapy: the future of allergy treatment[J]. Drug discovery today, 2016, 21(1): 26-37.