Infectious Diseases in the Head and Neck with Eosinophilia

Eosinophilia, defined as an elevated eosinophil count either in blood or tissue, has diverse implications for diagnosing and managing various diseases. Elevated eosinophil levels are often associated with conditions such as allergic reactions, autoimmune disorders, and specific infections. In the realm of head and neck pathology, eosinophilia can offer valuable insights into underlying infectious processes, which are often challenging to diagnose due to their overlap with other inflammatory and allergic conditions. This review describes the roles of blood and tissue eosinophilia in several infectious processes affecting the head and neck region. We focus on nine key conditions: allergic fungal rhinosinusitis, mycetoma, invasive fungal rhinosinusitis, rhinosporidiosis, baylisascariasis, toxocariasis, onchocerciasis, loiasis, and histoplasmosis. Allergic fungal rhinosinusitis, for example, is a hypersensitivity reaction to fungal antigens and is frequently associated with significant eosinophilic inflammation. Conversely, mycetoma, invasive fungal rhinosinusitis, and rhinosporidiosis may include eosinophils as part of a mixed inflammatory infiltrate. Histoplasmosis may also induce systemic eosinophilia as an atypical immune response to fungal infection. Additionally, baylisascariasis, toxocariasis, onchocerciasis, and loiasis are parasitic infections that often lead to systemic eosinophilia. By exploring these conditions, this review elucidates how identification of eosinophilia contributes to the diagnostic process. Understanding the association between eosinophilia and these infectious processes involving the head and neck is crucial for enhancing diagnostic accuracy, differentiating between similarly presenting conditions, and guiding effective treatment strategies.