CT Predictors of Poor Outcome in Chronic Hypersensitivity Pneumonitis

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In patients with chronic hypersensitivity pneumonitis, several parenchymal features on CT correlate with mortality and rapid disease progression, including honeycombing and reticular pattern.

Increased pulmonary vessel volume (PVV) in patients with chronic hypersensitivity pneumonitis (CHP) predicts mortality and an aggressive disease course similar to that of idiopathic pulmonary fibrosis (IPF), according to a study published in BMC Pulmonary Medicine.

Most patients with hypersensitivity pneumonitis who require specialist care have CHP, which in some patients is characterized by rapid fibrosis similar to that observed in IPF. Thus, it can be difficult to distinguish between CHP with an aggressive disease course and IPF. Since disease progression and prognosis of CHP are variable, the American National Heart, Lung and Blood Institute (NHLBI) and the Office of Rare Diseases have identified the need to better define the phenotypes of CHP as a research priority.

Quantitative computed tomography (CT) scores have been shown to correlate better with mortality in IPF than visual CT scores. Until recently, however, quantitative CT has not been evaluated as a tool to predict outcomes and prognosis in CHP.

Researchers, led by Joseph Jacob, MBBS(Hons), Bsc, MRCP, FRCR, MD(Res), from the Royal Brompton Hospital in London, investigated the visual and quantitative CT variables that predict poor IPF-like outcome in CHP patients without end-stage lung disease.

A total of 116 patients with CHP were evaluated with visual and computer-based (Computer Aided Lung Informatics for Pathology Evaluation and Rating [CALIPER]) measures of parenchymal features, which included honeycombing, ground glass opacities, total interstitial lung disease (ILD) extent, and PVV.

In the univariate analysis, both visual- and CALIPER-scored variables were identified as predictors of mortality in patients with CHP: honeycombing, visual traction bronchiectasis, reticular pattern, and CALIPER ILD extent (P <.05).

Higher PVV was the strongest independent risk factor for mortality and aggressive disease course in the multivariate analysis (P <.0001).

In order to establish a PVV threshold at which survival matches that of patients with IPF, survival in the patients with CHP was compared with that of 185 patients with IPF. At a PVV >6.5%, patients with CHP had a similar mean survival (35.3 months vs 38.4 months) and rapidity of disease progression as patients with IPF.

“In our study, almost 20% of CHP patients demonstrated an IPF-like outcome, and we could identify such patients using computer analysis of PVV,” Dr Jacob said in an interview with Pulmonology Advisor. “Clinicians treating patients with CHP should therefore be aware that a CHP diagnosis can portend a poor outcome. Identifying poor-outcome CHP patients may allow earlier institution of more aggressive or different therapeutic options, or earlier referral for lung transplantation.”

“We are not sure whether we are identifying a subset of CHP patients in which fibrosis predominates over an inflammatory etiology,” he added. “It could be postulated that the poor-outcome CHP patients may benefit from anti-fibrotic therapies as opposed to anti-inflammatory treatment alone.”

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Jacob J, Bartholmai BJ, Egashira R, et al. Chronic hypersensitivity pneumonitis: identification of key prognostic determinants using automated CT analysis. BMC Pulm Med. 2017;17(1):81. doi:10.1186/s12890-017-0418-2