Validation of symptom measures in patients under investigation for postural orthostatic tachycardia syndrome (POTS): The Orthostatic Grading Scale (OGS) and the Symptom Screen for Small-fiber Polyneuropathy (SSS)

Abstract

ObjectivesPostural Orthostatic Tachycardia Syndrome (POTS) presents with a range of poorly delineated symptoms across several domains. There is an urgent need for standardized symptom reporting in POTS, but a lack of validated symptom burden instruments. Our aim was to evaluate the psychometric properties of two symptom burden measures: the Orthostatic Grading Scale (OGS) and the Symptom Screen for Small-Fiber Polyneuropathy (SSS), in patients under investigation for suspected POTS. DesignPsychometric validation study. MethodsConfirmatory factor analysis (CFA) tested the factor structure of the SSS and OGS completed by 149 patients under investigation for POTS. Scale reliability and validity were assessed. The uni-dimensionality of the SSS was assessed through principal component analysis (PCA). ResultsCFA of the OGS revealed that a 1-factor structure had adequate fit. CFA of the SSS revealed that a 5-factor structure had generally appropriate fit supporting the originally proposed 5 factors (1: Gastrointestinal, 2: Somatosensory, 3: Miscellaneous, 4: Microvascular, and 5: Urological). In addition, the SSS demonstrated sufficient uni-dimensionality in the PCA, warranting use of a single total score. Omega coefficients of both measures indicated satisfactory internal reliability (0.668–0.931). Correlations with related constructs (distress (K10 score), r = 0.317–0.404, p < 0.001) and heart rate indices (with the OGS, r = 0.211–0.294, p < 0.05) suggested sound convergent and divergent validity. ConclusionsInitial evidence suggests that the OGS and SSS have good psychometric properties for use in populations with suspected and confirmed POTS.