Allergic Fungal Rhinosinusitis

Allergic fungal rhinosinusitis (AFRS) is a subset of chronic rhinosinusitis (CRS) with nasal polyps, which is characterized by the presence of eosinophilic mucin with fungal hyphae within the sinuses and a Type I IgE-mediated hypersensitivity to fungi. There is still debate on the pathophysiology and the classification of this special and interesting disease. More than three decades ago, AFRS had been described as a class of CRS by Miller and colleagues Later, Bent and Kuhn characterized the disease according to the presence of five distinct criteria: atopic history, nasal polyps, characteristic radiological findings, eosinophilic mucin without invasive findings and positive fungal stain. Pathological findings in AFRS may vary due to inflammatory response, which include eosinophil-predominant inflammation, Charcot–Leyden crystals (finding of eosinophil degranulation), and hyphae on fungal stain. Fungal species may vary and most common ones include Aspergillus, Alternaria, Bipolaris, and Curvularia. After the first presentation of AFRS as a distinct clinical entity, several reports have been published regarding its pathogenesis. Increased IgE production (with type 1 hypersensitivity reaction) has been revealed either on local sinonasal tissue or systemic circulation. This specific IgE may be linked to fungal and non-fungal antigens. Multiple Th2-based cytokines such as IL-4, IL-5, and IL-13 have been identified in the inflammatory response of AFRS.