Identifying causation in hypersensitivity pneumonitis: a British perspective

Abstract

BackgroundEstablishing whether patients are exposed to a ‘known cause’ is a key element in both the diagnostic assessment and the subsequent management of hypersensitivity pneumonitis (HP).ObjectiveThis study surveyed British interstitial lung disease (ILD) specialists to document current practice and opinion in relation to establishing causation in HP.MethodsBritish ILD consultants (pulmonologists) were invited by email to take part in a structured questionnaire survey, to provide estimates of demographic data relating to their service and to rate their level of agreement with a series of statements. A priori ‘consensus agreement’ was defined as at least 70% of participants replying that they ‘Strongly agree’ or ‘Tend to agree’.Results54 consultants took part in the survey from 27 ILD multidisciplinary teams. Participants estimated that 20% of the patients in their ILD service have HP, and of these, a cause is identifiable in 32% of cases. For patients with confirmed HP, an estimated 40% have had a bronchoalveolar lavage for differential cell counts, and 10% a surgical biopsy. Consensus agreement was reached for 25 of 33 statements relating to causation and either the assessment of unexplained ILD or management of confirmed HP.ConclusionsThis survey has demonstrated that although there is a degree of variation in the diagnostic approach for patients with suspected HP in Britain, there is consensus opinion for some key areas of practice. There are several factors in clinical practice that currently act as potential barriers to identifying the cause for British HP patients.

Occupation versus environmental factors in hypersensitivity pneumonitis: population attributable fraction

“…mould or birds), without distinguishing by source (occupational versus household). A recent series of 206 HP cases from the British Midlands is an exception [28]. It distinguishes, as we did also, mould-and avian-attributed diseases that are from occupational versus other sources (mould, 7 of 16 (44%); avian 4 of 37 (11%)).…”

Challenges in the Diagnosis and Management of Fibrotic Hypersensitivity Pneumonitis: A Practical Review of Current Approaches

“…Only 50% of MDD-diagnosed cases in another study of 251 initially undifferentiated ILD had diagnostic confidence >50% for f-HP using a similar algorithmic approach, mostly due to the absence or incompleteness of clinical or radiologic findings despite all patients having undergone histopathologic confirmation [ 81 ]. Barber et al reported a survey of British clinicians who described only 32% of their suspected HP cases had identifiable causative antigens, with 40% undergoing BAL and 10% undergoing surgical biopsy [ 82 ].…”

“…Varied use and clinical value attributed to certain diagnostic elements may bias decision-making in both algorithmic and MDD approaches [ 82 , 83 ]. For example, a plausible exposure history (pet bird owner) and typical radiologic findings may lead to a confident diagnosis without additional invasive testing, while initially unclassifiable ILD may still have a broad differential diagnosis that only tentatively includes f-HP if exposure history is dubious, a UIP-like CT pattern is encountered, and histopathology is only suggestive but not definitive for HP.…”

Fibrotic Idiopathic Interstitial Lung Disease: The Molecular and Cellular Key Players

“…Interstitial lung diseases are a broad spectrum of lung pathologies that can be divided into two groups: ILDs with a known cause and ILDs without a known cause that give rise to the idiopathic form of pulmonary fibrosis [2,3]. Furthermore, the possible causes of the ILDs identified are represented by systemic diseases such as connective tissue disease [4,5] or environmental exposure to pneumotoxic drugs [6], radiation therapy [6], occupational exposures (e.g., asbestosis) [7] or allergens in the case of hypersensitivity pneumonitis [8]. The discrimination among different ILDs that present hetherogeneous inflammatory and fibrotic patterns even among patients with the same disease is critical for a more predictable prognosis and a more efficient management of the patients.…”