Antibody type in AAV may help guide treatment for lung care, per study
CT scans show lung damage differs with ANCAs against MPO vs. PR3
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Lung damage in people with ANCA-associated vasculitis (AAV) can vary widely depending on the type of self-reactive antibodies driving the disease.
That’s according to the findings of a new study of AAV patients in Japan that used images from cast high-resolution CT scans, known as HRCTs.
Specifically, the data showed that individuals with antibodies against the myeloperoxidase (MPO) protein are more likely to develop lung scarring, or fibrosis. Meanwhile, lung cavities — hollow spaces that form when tissue breaks down —and nodules, or lumps, are more frequent among those with antibodies against the proteinase 3 (PR3) protein, the researchers noted.
The team said their findings may help doctors predict how a patient’s lungs will be affected, based on antibody type, and could help healthcare providers in choosing the most appropriate AAV treatment.
Still, “further multicenter, longitudinal [follow-up] studies are warranted to clarify differences in pulmonary involvement by [antibody] subtype,” the researchers wrote.
The study, “Differences in chest HRCT findings in relation to ANCA subtypes in ANCA-associated vasculitis,” was published in the journal Respiratory Investigation.
AAV is a group of diseases in which small blood vessels in the body become inflamed and damaged. It’s usually caused by self-reactive antibodies, known as ANCAs, that attack MPO or PR3 proteins on immune cells called neutrophils. Symptoms vary, but many patients develop problems in their lungs.
Previous studies have suggested that testing positive for antibodies against MPO may increase the risk of signs of interstitial lung disease (ILD), which causes scarring in the lungs, as observed on chest HRCT scans. These are detailed scans that show fine structures more clearly than standard chest imaging.
A large European study, meanwhile, found that a type of airway disease was “reported exclusively among patients with PR3-ANCA positivity,” the researchers noted.
Investigating the effects of antibody type on patients’ lungs in AAV
Now, a team of scientists from institutions across Japan set out to evaluate whether the type of HRCT-assessed lung lesions in AAV patients differs according to ANCA subtype. To do so, the scientists analyzed chest HRCT data at AAV diagnosis from 195 Japanese patients who were part of a larger study that followed AAV patients with rapidly progressing kidney disease.
The most common type of AAV among these individuals was microscopic polyangiitis, affecting nearly two-thirds of the patients. This was followed by granulomatosis with polyangiitis, seen in 15%, and eosinophilic granulomatosis with polyangiitis, affecting 9%. The remaining patients had no AAV type classification.
The majority overall — more than 80% — had antibodies against MPO. Nine patients (5%) had antibodies against PR3; eight (4%) had both types of antibodies; and 17 (9%) tested negative for either.
Most participants (88%) showed abnormal findings on chest HRCT scans. The most common (47%) was ground-glass opacity, which refers to a hazy area on the scan that looks slightly cloudy, suggesting inflammation or fluid in the lungs. This was followed by reticulation (41%), which refers to a net-like pattern that indicates scarring or thickening of lung tissue.
Traction bronchiectasis, which occurs when the airways are pulled and widened due to scarring of surrounding structures, appeared in about one-third of patients. Honeycombing, or clusters of small air spaces that resemble a honeycomb on imaging — and usually indicate advanced lung damage and scarring — was found in 25% of patients.
Study used data from chest CT scans known as HRCT s
When the researchers looked for differences in HRCT scan findings by ANCA subtype, they found that patients with anti-MPO antibodies alone were significantly more likely than those with anti-PR3 antibodies alone to have reticulation (43.5% vs. 0%). Honeycombing was also found just in the anti-MPO antibody group, but this difference only nearly reached statistical significance (29% vs. 0%).
In contrast, lung cavities were significantly more common in patients with antibodies against PR3 compared with those with anti-MPO antibodies (33% vs. 0%). So too were nodules, which are small, round lumps in the lungs (44% vs. 14%).
Nearly half of patients were diagnosed with interstitial pneumonia (IP), a group of diseases that cause inflammation and scarring in the tissue around the air sacs, and about one-third showed a definite usual interstitial pneumonia (UIP) pattern on HRCT scans.
The team found that IP was significantly more common in participants with anti-MPO antibodies (47 vs. 11%), as was a definite UIP pattern (41% vs. 0%).
“This study is the first to examine chest HRCT findings in Japanese patients with AAV in detail,” the researchers wrote. “IP with a definite UIP pattern was more frequent in patients with MPO-ANCA positivity while nodules and cavities were more frequent in patients with positive PR3-ANCA.”
The team noted, however, that future studies assessing chest HRCT scan findings over time, confirming such findings in lung biopsies, and including more patients with anti-PR3 antibodies are needed to better understand the link between lung manifestations and ANCA subtype.
