Smoking is most common preventable cause of early mortality/morbidity worldwide and has been associated with many diseases which include, also, interstitial lung diseases.
While there is strong epidemiological correlation between some of the interstitial lung diseases and smoking, scientific evidence is less accurate in rest, and cause-and-effect relationship has not been clearly established.
Although SR-ILD is rarer than other diseases caused by smoking, it may have of utmost importance. Among clinical, radiological differential diagnoses in smokers, keeping possibility of SR-ILD in mind is first step towards understanding diagnosis/treatment/prognosis.
In many cases of SR-ILD, complete recovery, regression, stabilization or slowing of progression were observed after smoking cessation.
It is very important to clarify diagnosis as new specific therapies have been developed for some types of SR-ILD. For example, antifibrotic drugs such as pirfenidone/nintedanib have been shown to slow progress of disease in patients diagnosed with IPF. In patients diagnosed with PAP, inhaled GM-CSF therapy is indicated if anti-GM-CSF antibodies is shown. There are studies on efficacy of BRAF-kinase inhibitor vemurafenib, which is used in treatment of systemic histiocytosis, in patients diagnosed as PLHH with mutation in BRAF-V600E gene.
Differential diagnosis in SR-ILD is important for evaluating need for additional treatment/prognosis. For example, smoking cessation in RB-ILD is mostly sufficient for recovery, no case of severe/ fatal progression has been reported in literature. However, in patients with DIP, steroid use is often required for disease stabilization. Moreover, progression is seen in 25% of patients, mortality is seen in 6-28% of patients with DIP despite proper treatment. In diseases with poor prognosis such as IPF, early diagnosis can positively influence survival of patients by providing early indication for lung transplantation.
In many SR-ILDs, clinical/radiological/histological findings are similar, overlapping, may be seen simultaneously. This overlap is observed especially between RB-ILD and DIP, these diseases are thought to correspond to different degrees of severity of same spectrum of diseases.
In same patient, different combinations of imaging findings of different SR-ILDs can be seen simultaneously, it may not always be possible to give single diagnosis. In patient followed with certain diagnosis of SR-ILD, findings of another SR-ILD may appear during follow-up. Knowing these is important for radiologist. In equivocal cases, patient history/examination findings/diffusion capacity measurement/spirometric tests/bronchoalveolar lavage findings/radiological imaging findings /if necessary, open lung biopsy results should be evaluated together. Interdisciplinary cooperation between chest physician, radiologist and pathologist will play key role in establishing clinico-radio-pathological correlation/reaching final diagnosis.
As conclusion, smoking related interstitial lung diseases should be kept in mind in differential diagnosis of smoking-patients. It is of great importance that radiologists should know characteristic imaging findings of these diseases for accurate diagnosis/treatment/prognosis evaluation. In many SR-ILDs, single diagnosis may not always be possible, as clinical/radiological/and histological findings may overlap. In uncertain situations, interdisciplinary cooperation should be ensured.