Introduction: Clubbing is very uncommon in respiratory bronchiolitis-associated interstitial lung disease, and primarily raises the suspicion of idiopathic pulmonary fibrosis in a patient presenting with diffuse parenchymal lung disease. If idiopathic pulmonary fibrosis can be excluded, clubbing should raise the suspicion of an occult tumour.
Case presentation: We describe a heavy smoker presenting with dyspnea and severe clubbing. Surgical lung biopsy revealed the histologic diagnosis of respiratory bronchiolitis-associated interstitial lung disease. Respiratory bronchiolitis-associated interstitial lung disease is a distinct clinicopathologic entity within idiopathic interstitial pneumonia patients described almost exclusively in cigarette smokers. The disease is associated with a good prognosis and mild symptoms but not with clubbing. After smoking cessation the radiologic findings of interstitial lung disease improved in parallel with improvement in lung function and gas exchange. However, a central squamous cell carcinoma was detected in the follow-up.
Conclusion: In this case, clubbing was most probably caused by the occult tumor rather than by respiratory bronchiolitis-associated interstitial lung disease.