A fourth diagnostic category of idiopathic pulmonary fibrosis (IPF) has been created to recognise the high frequency – about 30% – of atypical high-resolution CT (HRCT) features that accompany the usual interstitial pneumonia (UIP) histological pattern.
The 2018 update of the ATS/ERS/JRS/ALAT Clinical Practice Guideline for the Diagnosis of IPF recommends the addition of an indeterminate category to the UIP pattern, probable UIP and alternative diagnosis categories.
Professor Ganesh Raghu, from the University of Washington, said the role of HRCT was emphasised in the new guideline – either HRCT pattern of UIP alone or in specific combinations of HRCT patterns and histopathology where patients were subjected to lung biopsy.
However he told the ERS 2018 International Congress in Paris that diagnosis still relied first and foremost on the exclusion of known causes of interstitial lung disease (ILD).
The guideline therefore recommends a detailed history of medication use and environmental exposures to exclude conditions such as amiodarone toxicity or hypersensitivity pneumonitis, and serological testing to exclude underlying connective tissue disease.
“The majority of the panelists said we would test for ANA by immunofluorescence and ESR, CRP, anti-CCP and rheumatoid factor while some of the panel said they would also include muscle enzymes like creatinine phosphokinase, aldolase and myoglobin,” said Professor Raghu.
Cellular analysis of bronchoalveolar lavage fluid was recommended as a reasonable diagnostic intervention in patients clinically suspected of having IPF and with a HRCT pattern of probable UIP, indeterminate or an alternative diagnosis.
However it was not recommended for patients with a HRCT pattern of UIP.
Similarly the guidelines found the diagnostic benefits of surgical lung biopsy outweighed the risks in patients with a probable UIP, indeterminate or an alternative diagnosis but not in patients whose HRCT pattern was UIP.
Transbronchial lung biopsy was more contentious with the guideline development panel failing to reach a consensus about whether patients with an HRCT pattern of probable UIP, indeterminate, or an alternative diagnosis should routinely undergo the procedure, given the evidence that 64% would likely remain undiagnosed or proceed to a surgical lung biopsy.
It was however clear that the procedure offered no benefit to patients with a HRCT pattern of UIP.
Transbronchial cryobiopsy received a similar level of support with the panel concluding it might be reasonable for ‘experienced centres and experts with a track record’ to continue performing the procedure in patients with an HRCT pattern of probable UIP, indeterminate, or an alternative diagnosis.
“Those who have not yet begun to perform cryobiopsy should wait until the procedure has been standardised before implementing this into clinical practice,” the guideline said.
The panel said the potential downsides of cryobiopsy outweighed the potential benefits in patients with a HRCT pattern of UIP.
Professor Raghu said the benefit of a multidisciplinary discussion between pulmonologist, radiologist, pathologist and rheumatologist (depending on the case) was probably greatest in patients with an HRCT pattern of probable UIP, indeterminate, or an alternative diagnosis but recommended it for all patients with suspected IPF.
They also recommended against measuring serum biomarkers MMP-7, SPD, CCL-18, or KL-6 due to the high rates of false positive and false negative results likely to result in inappropriate therapy, delayed therapy or unnecessary additional diagnostic testing.