Population study suggests better AAV management in Sweden

Research shows incidence of AAV was stable over 23 years, as prevalence increased

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by Steve Bryson, PhD |

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The incidence of ANCA-associated vasculitis (AAV) in southern Sweden was stable over a 23-year period, while its prevalence, the total number of cases overall, increased, a study showed.

Stable incidence, or the same number of new cases per year, with a higher prevalence “might indicate better management and treatment of AAV resulting in improved survival,” the researchers wrote in “Stable incidence but increase in prevalence of ANCA-associated vasculitis in southern Sweden: a 23-year study,” which was published in RMD Open.

AAV comprises a group of autoimmune diseases marked by inflammation and damage to small blood vessels due to self-reactive antibodies, called ANCAs, being produced that wrongly target enzymes in certain immune cells.

“The reported incidence of AAV has increased globally in recent decades,” the researchers wrote, but with variations between different geographical regions.

Studies between 1998 to 2015 showed a wide variation in annual AAV incidence across European countries, with the highest seen in Norway (24.7 new cases per million inhabitants), followed by Sweden (20.8 per million) and the U.K (20.4 per million). The lowest annual incidence was reported in northern Germany with 10.2 per million.

“The increasing incidence might be partly explained by changes in classification criteria along with increased physician awareness and availability of ANCA testing,” the researchers wrote. These factors, plus improved diagnosis and rising survival rates, may also be behind a reported increase in AAV prevalence.

Researchers at Lund University, Sweden, have updated the incidence and prevalence of AAV in the country from 1997-2019. The team focused on a region in southern Sweden made up of 14 municipalities and with a mean population density more than 10 times higher than the country as a whole.

Using data from the local Skåne Healthcare Register (SHR), 374 people (47% women) were newly diagnosed with AAV in 23 years.

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Incidence of three AAV types over 23 years

Cases were classified based on AAV types — 192 with granulomatosis with polyangiitis (GPA), 159 with microscopic polyangiitis (MPA), and 23 with eosinophilic granulomatosis with polyangiitis (EGPA), the rarer type. A total of 188 patients were positive for ANCAs targeting the PR3 enzyme, 161 had anti-MPO antibodies, and 25 tested negative for ANCAs.

Results showed the mean annual incidence of AAV was 30.1 new cases per million adults. The incidence was highest for GPA (15.4 per million), followed by MPA (12.8), while EGPA showed a 10 times lower incidence at  1.8 per million.

Also, every year, men were more commonly affected by the disease than women (mean, 32.9 vs. 27.3 new cases per million adults).

Across three different periods — 1997-2003, 2004-2011, and 2012-2019 — the annual incidence of AAV was “relatively stable,” the researchers wrote, at about 30 new cases per million.

AAV incidence increased with age, with the highest being among those between 70-84, at 96.2 new cases per million adults. Men also had a higher incidence than women at 119.9 versus 77.8 cases per million.

GPA incidence was also highest in the 70-84 age group, at 43.2 new cases per million adults. EGPA incidence was highest in ages 55-69 years, at 4.4 cases per million.

The peak incidence of MPA was highest among those 85 and older at 56.8 cases per million. The team noted this might be explained by the age-related incidence increase among men, rising from 59.9 per million between 70-84 years to 78.9 per million among those 85 and older. MPA incidence in women was similar across age groups.

AAV was diagnosed mainly in the spring (29%), followed by summer (25%), autumn (24%), and winter (21%). Most cases were diagnosed in March and May, followed by April.

Using winter as a comparison, the likelihood of being diagnosed in the spring was 38% higher for all AAV, 43% higher for GPA, and 45% higher for MPA. EGPA was diagnosed most often in winter.

AAV prevalence, comorbidities

At the beginning of 2020, AAV prevalence was 428.4 cases per one million adults, with a median age of 71.5. The prevalence was higher among men than women (479.7 vs. 377.8 patients per million). GPA was the most prevalent AAV type at 241.6 cases per million, then 150.1 per million for MPA, and 36.6 per million for EGPA.

In comparison, AAV prevalence in 2003 was 353.6 cases per million adults, which rose to 434.7 per million in 2010 and 468.9 per million in 2015 — the “highest prevalence ever reported for AAV,” the researchers wrote.

Among the 220 AAV patients still living in the study area at the beginning of 2020, the most common comorbidity, or co-existing condition, was high blood pressure (50%), followed by cancer (27%) and diabetes (19.5%). Most patients (61%) had at least one comorbidity, while 39% had two.

“The increase in prevalence despite stable incidence might be attributed to improvements in patient survival, physician awareness and treatment,” the researchers wrote.