Smoking-related interstitial fibrosis- a case series

Smoking-related interstitial fibrosis (SRIF) is an increasingly recognized entity characterized by localized areas with respiratory bronchiolitis (RB), emphysema and interstitial fibrosis that occurs in smokers or former smokers. First described in 2010, the pathogenesis of SRIF remains unclear, although it is believed to be linked to inflammatory processes derived from smoking. The diagnosis is often accidental through pulmonary parenchyma samples obtained for other purposes, as it is not usually associated with significant respiratory symptoms. Transbronchial lung cryobiopsy (TBLC) is an accurate and safe procedure for diagnosing smoking-related interstitial lung diseases (ILDs).

This study presents a case series of 13 patients diagnosed with SRIF through TBLC. Patients were predominantly male (76.9%), with a median age of 55 years and a median smoking history of 44 pack-years. Common symptoms included cough (53.8%) and dyspnoea (30.8%), while 38.5% were asymptomatic. Lung Function Tests enclosed normal lung volumes but an impaired diffusion capacity (DL_CO). High-resolution computed tomography (HRCT) revealed centrilobular and paraseptal emphysema in all patients, with bilateral ground‒glass opacities in 81.8% of them. Histologically, SRIF was characterized by hyalinized alveolar septal fibrosis and intra-alveolar pigmented macrophages. Over the follow-up period, clinical evolution was variable, however, despite this inconsistency, this series seems to corroborate that the majority of the patients have a stable clinical course. Nonetheless, it must be underline that a subset experienced radiological or functional progression, particularly a decline in DLCO, although any case of progressive fibrosis associated with respiratory insufficiency was noticed. Still, the small sample size and observed variability, limits definitive conclusions about the overall natural history of SRIF. Based on the available data, no therapeutic intervention is recommended at diagnosis besides smoking cessation.

This case series highlights the mostly indolent nature of SRIF, although progression can occur in a subset of patients. The variability in clinical evolution underscores the importance of accurate diagnosis and individualized follow-up. Further prospective studies with larger cohorts are needed to clarify the natural history of SRIF and guide management strategies. Smoking cessation remains the primary intervention recommended at diagnosis.