RT Journal Article SR Electronic T1 Unclassifiable Interstitial Lung Disease (ILD). Why? JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society SP PA3756 DO 10.1183/13993003.congress-2021.PA3756 VO 58 IS suppl 65 A1 Elizabeth De Freitas Gonzalez A1 Carmen López Garay A1 Cristina Menéndez Sánchez A1 Carlos Mier Bango A1 Pablo Franco Suárez A1 Laura Sierra Herranz A1 Elena Bollo De Miguel A1 Javier Juan García A1 Nieves Alonso Orcajo A1 Juan Ignacio López Fernández A1 Silvia Fernández Huerga YR 2021 UL http://erj.ersjournals.com/content/58/suppl_65/PA3756.abstract AB Introduction: ILD compose a heterogeneous group of conditions demanding a multidisciplinary approach. However, a significant number of ILD cases must be labelled as ‘unclassifiable ILD’,common in fibrotic ILDObjective: To describe our patients showing unclassifiable ILD and the basis for diagnosisMethods: Retrospective descriptive study based on a database of patients assessed in ILD Specialized Unit and diagnosed with unclassifiable ILD (clinical, radiological and pathological findings did not suggest a specific diagnosis after assessment by an ILD multidisciplinary team)Results: 640 patients: 88 (14%), 55 ♂, 33 ♀, were diagnosed with unclassifiable ILD. Mean age: 70.85 ± 15.40 and 75.54 ± 10.36 in unclassifiable ILD cases. HRCT patterns:41 alternative diagnosis, 4 probable UIP, 11 indeterminate, 8 UIP, 11 NSIP, 13 other. 27 patients underwent bronchoalveolar lavage, 16 transbronchial biopsy and 1 surgical lung biopsy. Reasons for an unclassifiable ILD: old age (47), comorbidities (11), mild or stable disease (14), severe disease (4), patient declining surgical lung biopsy (2), and major discrepancies between clinical, radiological and pathological findings (10)Conclusions: A significant number of ILD cases are diagnosed as unclassifiable ILD, thus hindering pharmacological treatment. Survival is similar in patients with IPF or unclassifiable ILD. A greater use of antifibrotic therapy is advisable because most HRCT patterns present pulmonary fibrosis FootnotesCite this article as: European Respiratory Journal 2021; 58: Suppl. 65, PA3756.This abstract was presented at the 2021 ERS International Congress, in session “Prediction of exacerbations in patients with COPD”.This is an ERS International Congress abstract. No full-text version is available. Further material to accompany this abstract may be available at www.ers-education.org (ERS member access only).