Patients with granulomatosis with polyangiitis whose autoantibodies are against the myeloperoxidase protein (MPO) have increased disease activity at diagnosis but milder kidney manifestations than other vasculitis patients.
Based on findings from a retrospective analysis, a research team in China proposes that these patients should be considered a unique subtype of ANCA-associated vasculitis.
The study, “Myeloperoxidase-ANCA-positive granulomatosis with polyangiitis is a distinct subset of ANCA-associated vasculitis: A retrospective analysis of 455 patients from a single center in China,” was published in the journal Seminars in Arthritis and Rheumatism.
Microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA), the two most common subsets of AAV, are usually linked with a specific kind of autoantibody. While MPA is often associated with high levels of MPO antibodies, patients with GPA most commonly have PR3 autoantibodies.
Recent reports, however, suggest a clinically distinct subset of GPA patients with MPO antibodies. These patients have different clinical symptoms than the previously established subtypes.
The researchers had already shown that GPA patients with MPO antibodies are not rare in China. In this study, they set out to compare the clinical outcomes of these patients with those with MPA and MPO antibodies or those with GPA and PR3 antibodies.
Their analysis included 455 patients, including 280 with MPA and 175 with GPA. Most patients with MPA had antibodies against the MPO protein, with only four showing PR3 antibodies.
Among those with GPA, 124 were positive for the MPO antibodies, and only 51 presented antibodies against the PR3 protein.
Results showed that more patients with MPO-positive GPA had ear, nose, and throat involvement than those with MPO-positive MPA — 76.6 vs. 30.1%.
At diagnosis, these patients also had higher disease activity than those with MPO-positive MPA. No differences were seen when patients were compared with PR3-positive GPA patients.
However, patients with MPO-positive GPA had less severe renal symptoms and better kidney outcomes than patients with PR3-positive GPA. Additionally, their likelihood of developing end-stage renal disease was significantly lower than patients with MPO-positive MPA.
Overall, the researchers suggest that “MPO-ANCA positive GPA should be regarded as a unique subset of AAV. This subset of AAV patients had relatively milder renal injury.”
“Although ANCA specificities play an important role in differentiating AAV, taking the disease type together to classify AAV may be more rational,” they concluded.