Introduction Cough is a common but overlooked symptom in patients with interstitial lung disease (ILD). This study aimed to evaluate the cough characteristics and quality of life (QOL) of patients with ILD using a smartphone application and to assess its correlation with lung functions.

Methods From December 2021 to November 2022, patients with ILDs were prospectively enrolled at Seoul National University Bundang Hospital, South Korea. Coughs were recorded for seven days by a smartphone application (CoughyTM, Soundable Health, Inc). Pulmonary function tests, Leicester Cough Questionnaire (LCQ), and cough visual analogue scale (VAS) were collected at the enrollment.

Results Eighteen patients were enrolled in the study (idiopathic pulmonary fibrosis [IPF] 9, non-IPF-ILDs 9). The median age was 69.5 years, and 11 (61.1%) were male. The median cough frequency was 18.7 (12.7?42.3)/hr and tended to be more frequent during the daytime compared to nighttime. There were no significant differences in cough frequency according to sex and ILD subtypes. The median LCQ and VAS were 9.9 (6.5?11.9) and 5.0 (3.0?6.0), respectively. Cough frequency was significantly related to VAS (r=0.587, p=0.001) but not LCQ (r=-0.334, p=0.082). Diffusing capacity of the lungs for carbon monoxide (DLCO) showed a positive correlation with LCQ (r=0.643, p=0.005) and a negative correlation with nighttime cough (r = -0.520, p=0.032).

Conclusions In the current study, a smartphone application-based technique has demonstrated the potential to be a reliable option for evaluating cough in patients with ILDs. Reduced DLCO was related to the nocturnal cough and poor QOL in patients with ILDs.