Patient Global Impression of Severity Scale in Chronic Cough: Validation and Formulation of Symptom Severity Categories

Abstract

The Patient Global Impression of Severity (PGI-S) scale is a self-reported, single-item categorical scale that is increasingly used when assessing chronic cough (CC). This study aimed to establish validity, repeatability, and responsiveness of the PGI-S scale in CC and use the scale to define discrete categories of severity when measured with other commonly used patient-reported outcome (PRO) tools. Consecutive patients with CC completed the PGI-S scale, cough severity and urge to cough visual analog scales (VAS), and cough-specific health status Leicester Cough Questionnaire (LCQ) at a clinic visit. Validity, repeatability, and responsiveness were assessed, and threshold scores for PRO severity categories determined. A total of 482 participants completed the assessments; the median (interquartile range [IQR]) age was 57 (46-67) years, 71% were female, and the median (IQR) duration of cough was 48 (24-120) months. They reported a median (IQR) PGI-S score of 3 (3-4; moderate severity), cough severity VAS of 57 (31-75) mm, urge to cough VAS of 62 (40-81) mm, and LCQ of 11.5 (8.7-14.4). There were strong associations between PGI-S scores and cough severity VAS (ρ= 0.81), urge to cough VAS (ρ= 0.73), and LCQ (ρ=-0.73) (all P < .001). Repeatability of the PGI-S scale was high (n= 77); the intraclass correlation coefficient (95% confidence interval) was 0.85 (0.77-0.91) (P < .001). The PGI-S scale was responsive in participants with a treatment response (P< .001). The suggested PRO thresholds to define severe cough are ≥61 mm (cough severity VAS), ≥71 mm (urge to cough VAS), and ≤10 (LCQ). The PGI-S scale is a simple and valid tool that characterizes cough severity and is repeatable and responsive in CC. The proposed categorical severity thresholds for VAS and LCQ can provide intuitive meaning for patients and clinicians.