SCUAD and chronic rhinosinusitis. Reinforcing hypothesis driven research in difficult cases

Background: Our objective is to present recent research findings on recalcitrant chronic rhinosinusitis (CRS) in relation to "Severe Chronic Upper Airway Disease" (SCUAD). Methodology: Literature review using Medline and Embase databases (search terms 'chronic rhinosinusitis", "chronic sinusitis" or "Severe Chronic Upper Airway Disease") limited to articles published in the English language. Results: Complex pathophysiological mechanisms characterize various forms of chronic rhinitis and rhinosinusitis (CRS), where inflammation persists in spite of adequate medical treatment. In these cases, a multifactorial etiology often underlies the development of sino-nasal inflammation. The interaction between chronic upper and lower airway inflammation via neurogenic and systemic pathways may complicate the therapy of these patients, and lead to insufficient symptom control. Conclusion: The recently introduced definition of "Severe Chronic Upper Airway Disease" (SCUAD) increases awareness of those patients with persistent inflammation and symptoms despite guideline-driven pharmacologic treatment. The concept of SCUAD may prove helpful in directing research towards clarifying the definition, diagnosis and pathophysiology of rhinitis and rhinosinusitis, their limits and overlap. In this review, a hypothesis on SCUAD immunopathology is also presented.