Tuberous sclerosis complex (TSC) is a rare multisystem genetic disorder affecting almost all organs with no sex predominance. TSC has an autosomal-dominant inheritance and is caused by a heterozygous mutation in either the TSC1 or TSC2 gene leading to hyperactivation of the mammalian target of rapamycin (mTOR). TSC is associated with several pulmonary manifestations including lymphangioleiomyomatosis (LAM), multifocal micronodular pneumocyte hyperplasia (MMPH) and chylous effusions. LAM is a multisystem disorder characterised by cystic destruction of lung parenchyma, and may occur in either the setting of TSC (TSC-LAM) or sporadically (S-LAM). LAM occurs in 30–40% of adult females with TSC at childbearing age and is considered a nonmalignant metastatic neoplasm of unknown origin. TSC-LAM is generally milder and, unlike S-LAM, may occur in males. It manifests as multiple, bilateral, diffuse and thin-walled cysts with normal intervening lung parenchyma on chest computed tomography. LAM is complicated by spontaneous pneumothoraces in up to 70% of patients, with a high recurrence rate. mTOR inhibitors are the treatment of choice for LAM with moderately impaired lung function or chylous effusion. MMPH, manifesting as multiple solid and ground-glass nodules on high-resolution computed tomography, is usually harmless with no need for treatment.

Interstitial lung disease (ILD) refers to a large and heterogeneous group of parenchymal lung disorders [1], some related to other diseases such as connective tissue diseases (CTDs), some related to environmental exposures such as hypersensitivity pneumonitis, and others with an unknown cause and no identified aetiologic context. Idiopathic pulmonary fibrosis (IPF) is the most common type of idiopathic ILD, the most severe of the chronic forms of ILDs and represents, by definition, the prototype of progressive fibrosing ILD characterised by decline in lung function and early mortality [2]. In addition to IPF, a number of fibrosing ILDs can develop a progressive phenotype characterised histologically by self-sustaining fibrosis, a process common to a variety of conditions, and which leads to worsening quality of life, decline in lung function and, eventually, early mortality. Because these conditions share similarities regarding pathogenesis and clinical behaviour, they are increasingly described under the umbrella terminology of “progressive fibrosing ILDs” (PF-ILDs) or “fibrosing ILD with a progressive phenotype” [3, 4]. In this editorial, PF-ILDs will refer to fibrosing ILDs other than IPF which have a progressive phenotype.

Desquamative interstitial pneumonia (DIP) was originally described by LIEBOW et al. [1] in 1965, and so named because of the observation of cells filling the alveolar spaces and the belief that this feature was due to desquamation of alveolar epithelial cells. It has since been recognised that the dominant histologic feature of DIP represents accumulation of intra-alveolar macrophages, and sometimes of giant cells [2]. Although the more accurate terminology of “alveolar macrophage pneumonia” has been proposed, the term DIP has persisted [3]. In the international classification of idiopathic interstitial pneumonias [3], DIP and respiratory bronchiolitis-interstitial lung disease (RB-ILD) belong to the group of smoking-related interstitial pneumonia, together with pulmonary Langerhans cell granulomatosis. Depending on the classification, combined pulmonary fibrosis and emphysema, smoking-related acute interstitial pneumonia, smoking-related interstitial fibrosis, rheumatoid arthritis-associated ILD, and idiopathic pulmonary fibrosis may also be considered as smoking-related ILDs [4, 5].

Patient-reported outcome measures (PROMs), tools to assess patient self-report of health status, are now increasingly used in research, care and policymaking. While there are two well-developed disease-specific PROMs for interstitial lung diseases (ILD) and idiopathic pulmonary fibrosis (IPF), many unmet and urgent needs remain. In December 2019, 64 international ILD experts convened in Erice, Italy to deliberate on many topics, including PROMs in ILD. This review summarises the history of PROMs in ILD, shortcomings of the existing tools, challenges of development, validation and implementation of their use in clinical trials, and the discussion held during the meeting. Development of disease-specific PROMs for ILD including IPF with robust methodology and validation in concordance with guidance from regulatory authorities have increased user confidence in PROMs. Minimal clinically important difference for bidirectional changes may need to be developed. Cross-cultural validation and linguistic adaptations are necessary in addition to robust psychometric properties for effective PROM use in multinational clinical trials. PROM burden of use should be reduced through appropriate use of digital technologies and computerised adaptive testing. Active patient engagement in all stages from development, testing, choosing and implementation of PROMs can help improve probability of success and further growth.