Understanding patient experience of chronic cough in interstitial lung disease

Discussion

Our qualitative study on the experience of chronic cough in patients with ILD identified four major themes related to cough characteristics: triggers for cough, cough impacts, and educational needs and management, with two minor themes on cough interpretation and impacts of the COVID-19 pandemic.

In contrast to the common perception that cough due to ILD is non-productive [2, 11], the description of cough in our patients was variable. A surprising number of patients described productive cough, with sputum clearance occupying time and energy and impacting negatively on their HRQoL. As people with other co-existing respiratory diseases were excluded from this study, this may represent interindividual variation or the impact of other comorbidities on sputum production. In fact, many patients were aware of the contribution of relevant comorbid conditions to their cough. While most patients experienced cough predominantly during the day, some reported nocturnal symptoms, and these voiced concern about the impact on their loved ones’ sleep quality. Triggers for cough were diverse, and appeared to be relatively innocuous. Together with the commonly reported associated throat symptoms, these suggest an element of cough hypersensitivity [8] in these patients.

There are few reports in the literature assessing the impact and lived experience of chronic cough in people with ILD. The American Food and Drug Administration's Patient-focused Drug Development Initiative released a series of reports titled “The Voice of the Patient” in 2015 [12]. In facilitated discussion, participants described the inability to control coughing, often leading to episodes of shortness of breath, hypoxia or exhaustion. Triggers identified included physical activity, weather-related issues and speaking, all of which we have identified. Our in-depth one-on-one interviews and sampling of other ILD subtypes revealed additional aspects and impacts of cough including sputum production, triggers (lower respiratory tract infections, certain foods, stress and lifting heavy objects), physical symptoms (wheeze, sneezing, weight loss, dry retching) and impacts on work and vocational participation, social relationships and associated negative emotions.

The evidence supporting the management of chronic cough in ILD is limited [5]. Current guidelines recommend assessment for disease progression and complications of immunosuppressive therapy [5], with evaluation and management for other contributing factors according to general chronic cough guidelines [8]. The use of opiates for symptom control in the palliative care setting where other treatments have failed is recommended [5]. Among our patients, there was a strong theme of self-management, with many having tried several strategies and treatments for cough that were generally ineffective. This reflects the experience of many patients with chronic or refractory cough in general [13–15]. It was perceived that treatments were impractical or caused unwanted side effects. Although patients frequently described opiate-based linctus as effective, its use was limited by restrictions on driving, sedation and the small amount supplied on prescription resulting in rationing for emergencies or planned activities.

Patients with ILD and their caregivers have previously identified cough as a priority symptom [16] and have made it clear that they want to be educated about cough, even in the absence of evidence-based therapies [17]. In our study, patients commonly reported that management of cough was rarely discussed during the physician consultation. It is unclear whether the reluctance by physicians to discuss the symptom of cough is due to competing priorities and time pressure in the clinical consultation or a reflection of a lack of confidence and education in the assessment and management of cough due to the paucity of evidence in this area. There is a clear need for the development of effective antitussive medications and supportive therapies in ILD.

In order to assess the effectiveness of treatments for chronic cough in ILD in clinical trials, validated cough outcome measures, such as objective cough monitoring and cough quality of life questionnaires, should be used. Recommended patient-reported outcome measures for cough in current guidelines [5] include the Leicester Cough Questionnaire (LCQ) [18] and the Cough Quality of Life Questionnaire (CQLQ) [19]. However, these measures were developed in patients with non-ILD chronic cough, and their development was not informed by qualitative data obtained from patients with ILD at inception. While they cover some of the characteristics and impacts that have emerged in this study, they do not capture all ILD-specific aspects of chronic cough, particularly related to disease progression and treatments. For instance, an item in the LCQ asks whether “cough may indicate a severe illness” and in the CQLQ “I am concerned that I have cancer because of my cough”, which focuses on the evaluation in patients without a clear diagnosis that can be attributed for their cough and are of less relevance for patients with ILD. Items asking patients whether they associate cough with concerns of ILD progression or exacerbation and their experience of breathlessness related to cough may be more relevant. Similarly, the King's Brief Interstitial Lung Disease Questionnaire [20], a HRQoL questionnaire that is commonly used in clinical trials, only provides a brief assessment of chest symptoms such as tightness and wheeze and does not adequately cover the aspects of cough highlighted by patients in this study.

Themes related to cough characteristics and impacts on quality of life identified from this study will be useful in the future development of an ILD-specific cough questionnaire. A recently published conceptual framework for the development of cough symptom severity in patients with refractory or unexplained chronic cough identified two broad domains: urge to cough sensations (frequency and intensity) and cough symptom (triggers, control, frequency, fit/bout duration, intensity, quality, associated features) [21]. Differences in the associated features described by patients with ILD compared to those with refractory or unexplained cough include significant breathlessness and fatigue predominating, while pain and dizziness were not a feature of our interviews. In this study patients also clearly described the impacts on social and emotional function, as well as their connotation of increased cough severity with worsening of disease and lung function. Additional themes on educational needs and self-management as well as impacts of the COVID-19 pandemic in our interviews highlight patient needs and support future research to advance management of chronic cough in ILD.

The strengths of this study are the in-depth exploration of different aspects of chronic cough with ILD encompassing its nature, impacts and management in ILD. While qualitative interviewing has been undertaken previously in patients with ILD to assess their HRQoL, none has directly focused on the cough symptom. Limitations include recruitment from a single centre and sampling of three subtypes of ILD. Purposeful sampling may introduce observer bias. However, it was necessary to ensure good representation with inclusion of patients with common ILD subtypes and disease severities from different demographic backgrounds. All patients were English-speaking, reducing the generalisability to patients with ILD from non-English-speaking backgrounds. We conducted telephone interviews due to the restrictions of the COVID-19 pandemic. While this increased the geographical variation, it may have limited the non-verbal information we could gather. The perspectives of carers and family members were not formally captured in this study, although carers were present in some interviews providing little direct information.