Anosmia and hyposmia are symptoms of CRS both with and without nasal polyps and can significantly affect quality of life. The nature of anosmia/hyposmia is thought to be both sensory-neural and conductive. These authors studied a mouse model in which type 2 T-Helper allergic CRS was induced. Allergens were house dust mite and staphylococcus enterotoxin B. The focus of study was the olfactory epithelium in addition to assessment of sense of smell via electro-olfactogram and olfactory behaviour.
After 22 weeks of allergen treatment IL13, IL4, IL5 mRNA levels increased significantly in the allergic group as compared to controls. IL13 increased 51-fold. Additionally, mast cells and eosinophil were found in olfactory epithelium.
Eosinophils infiltrated deeper and were closer to nerve bundles. They also found that number of immature olfactory sensory neurons has decreased but not the mature ones. More importantly, sense of smell does not seem to be affected. Authors concluded that immature olfactory neurons decrease in type 2/Th2 response within the olfactory area. They also mentioned that this might be responsible in part for hyposmia/anosmia in CRSwNP patients. This is an interesting study, which could help explain our failures in regaining sense of smell in our CRS patients. I am in agreement with the authors’ views on the short study period which could be the reason why the sense of smell did not seem to be affected, and also regarding the differences between humans and mice in terms of olfactory epithelium properties that might prevent transferability of conclusions.