Abstract
To determine the prevalence, characteristics, and outcomes of patients with unclassifiable interstitial lung disease (ILD) and develop a simple method of predicting disease behaviour.
Unclassifiable ILD patients were identified from an ongoing longitudinal cohort. Unclassifiable ILD was diagnosed when multidisciplinary review did not secure a specific ILD diagnosis. Clinical characteristics and outcomes were compared with idiopathic pulmonary fibrosis (IPF) and non-IPF ILDs. Independent predictors of mortality were determined using Cox proportional hazards analysis to identify subgroups with distinct disease behaviour.
Unclassifiable ILD was diagnosed in 10% of the ILD cohort (132 of 1370 patients). The most common reason for being unclassifiable was missing histopathological assessment due to a high risk of surgical lung biopsy. Demographic and physiologic features of unclassifiable ILD were intermediate between IPF and non-IPF disease controls. Unclassifiable ILD had longer survival compared to IPF on adjusted analysis (hazard ratio 0.62, p=0.04) and similar survival compared to non-IPF ILDs (hazard ratio 1.54, p=0.12). Independent predictors of survival in unclassifiable ILD included DL,CO (p=0.001) and radiological fibrosis score (p=0.02).
Unclassifiable ILD represents approximately 10% of ILD cases and has a heterogeneous clinical course that can be predicted using clinical and radiological variables.
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