Charcot Leyden crystals (CLC) are sometime reported in pathological reports of airway or sinonasal samples but their clinical significance remain elusive. The investigators organized a retrospective analysis of all consecutive patients with CLC seen at our institution between 1986 and 2019

In recent years, improved knowledge of eosinophilic inflammation has led to the approval of biologics aimed at inhibiting the pathways of eosinophilic activation, notably via the interleukin 5 pathway in eosinophilic asthmatic patients uncontrolled despite receiving maximum doses of standard drugs. These treatments showed efficacy in asthmatic patients with a high level of eosinophils in their induced sputum (> 3%) and the criteria were extended to those with circulating eosinophilia (> 300 / mm3). Eosinophils are therefore an important biomarker for phenotyping asthmatic patients. The Charcot-Leyden crystals are a reflection of the presence of eosinophils, and are sometimes found in some pathological samples. It is hypothesized that the presence of Charcot-Leyden crystals, a reflection of tissue eosinophilia, is a predictive factor for the efficacy of anti-IL5 biotherapies in patients with severe eosinophilic asthma.

Inclusion Criteria:

• Having Charcot Leyden Crystals in a pathological sample

Exclusion Criteria:

• Having Charcot Leyden Crystals in a pathological sample taken outside the airways the nose and the sinus

Consecutive patients seen at our institution

NC