Patterns of Lung Disease Differ According to AAV Type, Study Says

Interstitial lung disease may occur early or in the course of AAV

Somi Igbene, PhD avatar

by Somi Igbene, PhD |

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The occurrence of interstitial lung disease (ILD) and its pattern on high-resolution imaging scans vary according to the profile of self-reactive antibodies in patients with ANCA-associated vasculitis (AAV), according to a recent study.

Granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) are two types of ANCA-associated vasculitis. ILD was already evident at AAV diagnosis in 66.3% of the patients in the study, with most displaying a nonspecific interstitial pneumonia pattern.

The study, “Interstitial lung disease in microscopic polyangiitis and granulomatosis with polyangiitis: demographic, clinical, serological and radiological features of an Italian cohort from the Italian Society for Rheumatology,” was published in the journal Clinical and Experimental Rheumatology.

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AAV occurs when the immune system attacks small blood vessels in different organs and tissues, damaging them. This attack is triggered by self-reactive antibodies called anti-neutrophil cytoplasmic autoantibodies (ANCAs) that typically target one of two proteins: proteinase 3 (PR3) or myeloperoxidase (MPO). Most patients with MPA carry antibodies against the MPO protein (MPO-ANCAs or perinuclear ANCAs), while those with GPA typically have antibodies against PR3 (PR3-ANCAs or cytoplasmic ANCAs).

ILDs are diseases that cause lung tissue scarring (fibrosis). Although they occur frequently in people with GPA and MPA, how early they develop, their pattern on CT scans, and their association with ANCA subtypes are unclear.

To learn more, a team of Italian scientists studied patients with ILD and a confirmed MPA or GPA diagnosis. Patients provided blood samples to determine if they had MPO- or PR3-ANCAS.

ILD patterns on high-resolution computed tomography scans were classified into three groups: usual interstitial pneumonia (UIP), nonspecific interstitial pneumonia (NSIP), or organizing pneumonia. In cases where patients showed a pattern of indeterminate UIP, the pattern was further classified as NSIP, organizing pneumonia, or other.

A total of 95 patients were enrolled in the study. From these, 58.9% had MPA and 41.1% had GPA. A total of 68.4% were positive for perinuclear ANCAs (p-ANCAs), while 24.2% had cytoplasmic ANCAs (c-ANCAs), and 7.4% were ANCA-negative.

Nonspecific interstitial pneumonia most common pattern detected

NSIP (51.6%) was the most common pattern on imaging scans detected, especially in GPA patients (76.9%), followed by UIP (37.9%) which was seen more frequently in patients with MPA (48.2%).

ILD was diagnosed before AAV in 22.1% of the patients, at the same time in 44.2%, and after AAV diagnosis in 33.7%. The disease was more likely to be detected before AAV in p-ANCA-positive patients, and the ILD pattern was mainly usual interstitial pneumonia. Conversely, ILD was seen after AAV diagnosis more frequently in c-ANCA-positive patients, and these patients were more likely to have the NSIP pattern. Most (85.7%) ANCA-negative patients showed an NSIP pattern; for 42.8% of them, ILD was diagnosed after AAV.

“Our data confirm that UIP is the prevalent pattern observed in p-ANCA positive patients (47.7%), but we also observed that NSIP is predominant in c-ANCA positive and ANCA negative cases,” the researchers wrote.

Based on these findings, AAV patients with ILD can be classified into two categories, the researchers wrote. The first includes patients whose ILD was apparent before AAV diagnosis. These patients are usually positive for p-ANCAs and display a UIP pattern. The team suggested that a pulmonologist must carefully assess these patients to ensure adequate treatment, as they are often misdiagnosed with idiopathic pulmonary fibrosis (IPF), a form of ILD.

Additionally, “this subgroup of patients has a poor prognosis more related to ILD than to vasculitis, and, in analogy to IPF, anti-fibrotic agents might be useful,” the researchers wrote.

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In the second category, ILD is detected at the same time as AAV, or arises over the course of the disease. These patients usually present with an NSIP pattern and are often c-ANCA positive or ANCA-negative. They, especially those with GPA, must also be adequately assessed by a pulmonologist.

“Our study confirms that UIP is a frequent pattern of lung disease in AAV-ILD patients,” the researchers wrote. “Our results also suggest that ILD can represent an early complication of AAV but also occur in the course of disease, suggesting the need of a careful evaluation by both pulmonologist and rheumatologist to achieve an early diagnosis.”

The researchers also noted that more studies with larger and more uniform patient populations are needed to characterize the prevalence and progression of ILD in AAV and to develop effective therapeutic strategies.