The SNOT-22 factorial structure in European patients with chronic rhinosinusitis: new clinical insights

PURPOSE: The sino-nasal outcomes test-22 (SNOT-22) represents the reference questionnaire to assess patients with chronic rhinosinusitis (CRS). As weak correlations between objective CRS parameters and SNOT-22 total score have been observed, factor analyses have aimed to identify underlying factorial structures. However, ambiguous factor loadings and problematic item-domain assignments have resulted. Moreover, such factor analyses have mainly been performed in non-European CRS patients, while European data remain sparse. This study thus sought to address these issues. METHODS: Principal component analysis and confirmatory factor analysis were performed from SNOT-22 questionnaires completed by European CRS patients. Goodness of fit, internal consistencies, and factor loadings were calculated. Item-domain assignment was based on statistical grounds and clinical meaningfulness. Additionally, this study investigated correlations between SNOT-22 domains and external reference criteria, including Lund–Mackay score, Lund–Naclerio score and the brief symptom inventory 18 (BSI-18). RESULTS: One hundred and thirty-four European CRS patients were included. Principal component analysis proposed four SNOT-22 domains (“nasal symptoms”, “otologic symptoms”, “sleep symptoms”, “emotional symptoms”), which explained 63.6% of variance. Observed item-domain-assignment differed from previously proposed item-domain assignments. All factor loadings were > 0.5, except “cough” (0.42) and “facial pain or pressure” (0.49). For confirmatory factor analysis, satisfactory goodness of fit (RMSEA = 0.66; CFI = 0.92; TLI = 0.90) and internal consistencies (Cronbach-α: total score = 0.93; domains = 0.75–0.91) were observed. Significant positive correlations were found between the “nasal symptoms” domain and both the Lund–Mackay score (r = 0.48; p < 0.001) and the Lund–Naclerio score (r = 0.27, p < 0.01). Significant positive correlations were also identified between “emotional symptoms” and BSI-18 total score (r = 0.64, p < 0.001). CONCLUSIONS: Principal component analysis performed for SNOT-22 questionnaires completed by European CRS patients indicated a different item-domain-assignment than previously reported. Confirmatory factor analysis suggested acceptable and clinically plausible psychometric properties for the resulting factorial structure. Significant correlations between the “nasal symptoms” and the “emotional symptoms” domains were observed with objective CRS parameters. The resulting factorial structure with different item-domain assignments may thus be more suitable for European CRS patients.