Longitudinal evaluation of clustering of chronic sinonasal and related symptoms using exploratory factor analysis

Abstract

Background: Sinonasal symptoms are common and can have several underlying causes. When symptoms occur in specified patterns lasting 3 months or more they meet criteria for chronic rhinosinusitis (CRS). Approaches to CRS symptom measurement do not specify how to measure symptoms and treat specified sinonasal symptoms as generally interchangeable, suggesting that such symptoms should cluster on 1 or 2 latent factors.

Methods: We used questionnaire responses to 37 questions on the presence, severity, bother, and frequency of cardinal sinonasal and related symptoms lasting 3 months, from 3535 subjects at 3 time points over 16 months. We completed 5 exploratory factor analyses (EFA) to identify symptom clustering, 1 for each time point and 2 for the differences between adjacent questionnaires. The baseline EFA was used to provide factor scores that were described longitudinally and examined by CRS status.

Results: Five EFAs identified the same 5 factors (blockage and discharge, pain and pressure, asthma and cold/flu symptoms, smell loss, and ear and eye [mainly allergy] symptoms), with clustering determined by symptom frequency, severity, and degree of bother. Responses to individual questions showed changes over time but when combined into factor scores showed less longitudinal change. All symptom factor scores were progressively higher from never to past to current CRS status.

Conclusions: Although the current approaches to symptom characterization in CRS imply a single underlying latent construct, our results suggest that there are at least 3 latent constructs relevant to CRS. Further studies are needed to evaluate whether these clusters have identifiable underlying pathobiologies.

Keywords: chronic rhinosinusitis; exploratory factor analysis; longitudinal; nasal and sinus symptoms; population-based epidemiology.

Figure 1.

Lasagna plot displaying the proportion of individuals with each given response to the question “On average, how often in the past 3 months have you had post-nasal drip?” at baseline and 6 months and 16 months later (1 = never, 2 = once in a while, 3 = some of the time, 4 = most of the time, 5 = all the time). Y-axis values indicate the number of subjects with specific responses at baseline.

Figure 2.

Factor 1 (blockage and discharge) scores by EPOS_s CRS groups (current, past, never) at baseline. The number of subjects in each group is indicated. Factor scores were estimated by the item response theory (IRT) method. The X-axis was jittered to improve readability.

Figure 3.

Continuous factor scores categorized to show longitudinal change across questionnaires for factor 1 (blockage and discharge). Factor scores were categorized as: factor score < −0.4 were assigned values of −1; between −0.4 and 0.6, assigned 0; between 0.6 and 1.2, assigned 1; and > 1.2, assigned 1.3. The Y-axis labels indicate the number of subjects at baseline in each adjusted factor score group. Factor scores were estimated by the item response theory (IRT) method.