Respiratory bronchiolitis associated interstitial lung disease (RBILD)/desquamative interstitial pneumonia (DIP) presenting as cystic lung disease.

Desquamative Interstitial Pneumonitis (DIP) is included in the differential diagnosis of cystic lung disease. To our knowledge there have been only 5 cases reported of this association. We report a patient that presented with diffuse cystic lung disease that on biopsy was demonstrated to have Respiratory Bronchiolitis Interstitial Lung Disease (RB-ILD), considered part of the spectrum that includes DIP. Case presentation: A 57 year-old Black female was referred to the pulmonary clinic with progressive exertional dyspnea over several months. A lung cancer screening CT scan showed diffuse cystic lung disease with associated ground glass opacities and emphysematous changes. There were several nodules, the largest was 7mm. Spirometry showed mild obstruction with severe diffusing impairment. The patient refused interventional diagnostic evaluation, but agreed to a trial of bronchodilator therapy, to try to stop smoking, and return for follow up CT scan in 3 months. When she did not return for the scheduled CT scan, she was contacted by phone eventually she did return to the pulmonary clinic for follow up eight months later experiencing worsening dyspnea. She had not stopped smoking and now required supplemental O2 of 2 liter for hypoxemia. She consented to a wedge biopsy that showed cysts associated with RB-ILD/DIP. Immunohistochemical staining was negative for Lymphangioleiomyomatosis and Langerhans cell histiocytosis. Genetic testing for Birt Hogg Dube Syndrome was recommended and requested but the patient is yet to complete testing. She did not however have any concerning features of skin disease, renal disease or malignancy. Discussion and relevance: Diffuse cystic lung diseases are associated with multiple etiologies. RB-ILD/DIP usually presents in smokers with symptoms of dyspnea and findings of bronchial wall thickening and ground-glass attenuation and may coexist with emphysema. In the largest published series of the association of cystic lung disease in DIP, 5 of 22 patients on long-term follow-up developed new cysts. This case is being presented to highlight smoking related RB-ILD/DIP) as a cause of cystic lung disease and to our knowledge is the 6th case on reported