More research is needed for local allergic rhinitis.

many patients are referred to the allergy clinic long after disease onset. In 2014, we published the initial results of a 10-year follow-up study of LAR [8] . We included a cohort of 194 LAR patients (<2 years of evolution) and 130 healthy controls evaluated yearly. After 5 years, patients and controls had a similar rate of conversion to SAR (6.8 and 4.5%, respectively). These data contrast with the findings of Sennekamp et al. [1] . In their retrospective study, they evaluated the longterm conversion rate from LAR to SAR based on medical records [1] . They selected 42 patients with positive reactions to nasal allergen provocations but with a negative skin test (ST) to the same allergen (but not necessarily to others), who had attended their center from 1982 to 2012 and who had repeated the ST at least once during the study. They reported that negative ST reactions were converted into positive ones in 17 patients (40%). Although such retrospective studies can be of value for estimating changes in disease prevalence and evolution, they are subject to several biases. The patients included attended the clinic more than once and thus were more likely to have more severe and/or persistent symptoms. However, milder cases that did not Dear Editors, We read with interest the work by Sennekamp et al. [1] demonstrating that patients with local allergic rhinitis (LAR) may progress to systemic allergic rhinitis (SAR) over time. Although LAR was first reported in the 1970s [2] and many clinicians observed patients with this entity [3–5] , this issue has not been studied in sufficient detail and deserves more attention [6, 7] . In fact, we have observed patients with LAR symptoms in our center for more than 30 years, but we have not had the resources to study it in depth until recently. To our surprise, LAR is currently a subject of debate because, although it is frequently reported by some, it is rarely noted by others. This may be due to the system of patient referral to tertiary specialized centers as well as differences in the prevalence between populations [6, 7] . In our view, more studies estimating the prevalence, significance and natural history of LAR are needed in adult and pediatric populations. Follow-up studies including patients and exposed controls are the most adequate approach to evaluate the natural evolution of diseases. Where possible, patients should be studied from the beginning in order to avoid survival bias [8] . However, this is often very difficult because Received: May 18, 2015 Accepted after revision: June 11, 2015 Published online: July 22, 2015