Low BMI in Older MPA Patients Linked to High Infection Risk

Being underweight at diagnosis, with a low body mass index (BMI), is associated with a significantly greater risk of severe infections in older adults with microscopic polyangiitis (MPA), a recent study in Japan reports.

Other significant predictors of severe infection included older age and the use of the immunosuppressant methylprednisolone as a pulse therapy.

Patients meeting these conditions should be more carefully monitored to reduce their risk of infections, especially in the first year following diagnosis, the researchers said.

The study, “Association between body mass index and severe infection in older adults with microscopic polyangiitis: a retrospective cohort in Japan,” was published in BMC Geriatrics.

Individuals with ANCA-associated vasculitis (AAV), a group of autoimmune diseases, are at a much higher risk for infections than the general population. Among the known risk factors for severe infections in AAV patients are the use of immunosuppressants and high-dose glucocorticoids, older age, low white blood cell count, and kidney problems.

However,  the association between nutritional status and severe infection in older AAV patients is not well understood.

Now, researchers at the Aichi Medical University, in Japan, and their colleagues sought to investigate the potential relationship between BMI — body mass index, a measure of body fat — at diagnosis and the risk of severe infection in AAV patients over the age of 65.

Their study enrolled a total of 93 patients with MPA — the most common type of AAV — treated at a rheumatology center in Japan between 2004 and 2018. Of them, 22 had a low BMI, of less than 18.5 kg/m2, while 53 had a normal BMI, with scores ranging between 18.5 and 23 kg/m2. The remaining 18 participants had a high BMI, above 23 kg/m2.

The groups were generally similar in their clinical and disease characteristics, but the low BMI patients more often had experienced unintentional body weight loss in the six months preceding their diagnosis, as compared with the high BMI group.

Over a median follow-up of 19 months (about 1.5 years), a total of 29 patients (31.2%) experienced 34 severe infections — five patients (5.4%) had two severe infections.

Patients with low BMI at diagnosis were more likely to develop severe infections than the other two groups, the data showed. In the first year after diagnosis, the cumulative probability of severe infection was 0.52 for the low BMI group, 0.2 for the normal BMI group, and 0.06 for the high BMI group. Within five years of diagnosis, the risks had climbed for all three groups, to 0.64 for those with initially low BMI, 0.32 for the normal BMI group, and 0.18 for those who had initially had high BMI.

“Most infection-related events developed during the first year after AAV diagnosis in the low BMI group,” the investigators wrote. “This result suggests that physicians should pay attention to development of infection, especially during the first year of treatment after diagnosis of AAV.” 

Statistical analysis demonstrated that older age, low BMI — as compared with normal BMI — and the use of methylprednisolone pulse therapy were all significant predictors of severe infections, even after adjusting for confounding factors like age, sex, lung involvement, and diabetes. A confounding factor is an additional variable in a study examining a potential cause-and-effect relationship.

Notably, patients with severe infections more often had a decrease in body weight, used methylprednisolone, or died than those without infections. 

Among the study’s limitations were its retrospective and observational nature, the inability to adjust for the effects of underlying immune conditions, and the inclusion of only older patients with MPA from Japan. Additionally, researchers were unable to assess the frequency of glucocorticoid use or the nutritional status using methods other than BMI, which also may limit the study’s conclusions.

Nevertheless, being underweight at diagnosis did raise concern for investigators.

“Our results suggested that malnutrition at diagnosis might increase vulnerability to infection during immunosuppressive treatment, especially in older adults,” the researchers concluded, adding,  “Physicians should closely follow-up older adults with MPA and low BMI to monitor them for the development of infections.”