ArticlesChronic hypersensitivity pneumonitis in patients diagnosed with idiopathic pulmonary fibrosis: a prospective case-cohort study
Introduction
Idiopathic pulmonary fibrosis (IPF) is a distinct fibrotic lung disease manifesting in adults, and its diagnosis and clinical features have been well established in evidence-based guidelines.1 The annual incidence in the USA2 between 1996 and 2000 ranged from 1·2 to 76·4 per 100 000 person-years using narrow or broad criteria and is 7·4 per 100 000 person-years in the UK.3 The prognosis of IPF is very poor, with mean survival varying from 3–5 years.1, 4 The 2011 guidelines1 for diagnosis and management of IPF emphasise the need to exclude all known causes associated with interstitial lung diseases or pulmonary fibrosis; however, the burden of this elimination and the clinical index of suspicion for diagnosis of hypersensitivity pneumonitis rests on the individual clinician and their investigation. In this respect, environmental factors at home and at work are very important, not only to aid in the correct diagnosis but also to recommend avoidance of further exposure to the identified antigen or factor because this is prudent to the management of patients with interstitial lung diseases or pulmonary fibrosis. To pursue such preventive measures, proactive efforts are needed to identify potential environmental factors that might cause pulmonary fibrosis.
In the appropriate clinical setting, the presence of radiological or histopathological features of usual interstitial pneumonia is a diagnostic criterion for IPF.4 However, this characteristic pattern of usual interstitial pneumonia is not pathognomonic of IPF because it has been observed in patients with chronic hypersensitivity pneumonitis, collagen vascular diseases, asbestosis, and other contexts.5, 6, 7, 8 Thus, some patients diagnosed with IPF might in fact have chronic hypersensitivity pneumonitis and exposure to the antigen might have been occult or forgotten.9, 10 Exposure to avian antigens by contact with birds is a well recognised common cause of hypersensitivity pneumonitis (so-called bird fancier's lung), but exposure can also occur in circumstances other than by direct contact with live birds. One such situation is exposure through feather bedding use, which in susceptible individuals can lead to development of the hypersensitivity pneumonitis named feather duvet lung.11, 12, 13, 14
We aimed to test the hypothesis that some patients diagnosed with IPF on the basis of the 2011 guidelines actually have chronic hypersensitivity pneumonitis caused by exposure to an occult antigen or antigens known to cause hypersensitivity pneumonitis. We believe that inconspicuous but persistent exposure to such antigens might provoke asymptomatic lung disease that goes unnoticed until it has progressed to stages of pulmonary fibrosis with features of usual interstitial pneumonia and is eventually misdiagnosed or labelled as IPF. Furthermore, such occult factors can only be identified with meticulous protocolised clinical, immunological, and pathological study to allow accurate diagnosis and appropriate treatment intervention.
Section snippets
Study population
In this case-cohort study, from Jan 1, 2004, to Dec 31, 2009, 305 consecutive and previously unreported outpatients were prospectively evaluated within the interstitial lung diseases programme of Hospital Universitari Vall d'Hebron (Barcelona, Catalonia, Spain) in accordance with a research protocol approved by the centre's ethics committee. All patients seen in the interstitial lung diseases clinic during the study period and diagnosed with IPF on the basis of international guidelines
Results
Of the 46 patients who met the 2011 criteria for IPF, 16 (34%) had been exposed to feather duvets or pillows and ten (63%) of these 16 patients were diagnosed with chronic hypersensitivity pneumonitis. Among the 30 of 46 patients who did not have a history of exposure to feather duvets or pillows, ten (33%) were diagnosed with chronic hypersensitivity pneumonitis (figure). Altogether, 20 (43%, 95% CI 29–58) patients were identified as having chronic hypersensitivity pneumonitis during the
Discussion
In this prospective observational study of consecutive patients with well defined IPF in accordance with the current 2011 criteria for diagnosis of IPF,1 a third of patients on further history elicitation and leading questionnaires had occult exposure to feather duvets or pillows and two-thirds of those patients exposed were diagnosed with chronic hypersensitivity pneumonitis (panel 2). Altogether, almost half of patients diagnosed with IPF on the basis of the 2011 criteria had a final
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