Association between body mass index and severe infection in older adults with microscopic polyangiitis: a retrospective cohort in Japan

BACKGROUND: Although previous studies have evaluated risk factors for the incidence of severe infection in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV), the relationship between body mass index (BMI) and severe infection in AAV has not been elucidated. We hypothesized that older adults with AAV and a low BMI would be at a higher risk of infection. We therefore investigated the association between underweight status at AAV diagnosis and subsequent occurrence of severe infection in older adults with AAV. METHODS: This single-center retrospective cohort study included 93 consecutive older adults with microscopic polyangiitis (MPA) treated at the Aichi Medical University Hospital in Japan between 2004 and 2018. The relationships between BMI at diagnosis and subsequent first severe infection were assessed using multivariate Cox proportional hazards models. The cumulative probability of the development of the first severe infection was calculated using the Kaplan-Meier method and the log-rank test. The level of statistical significance was set at P < 0.05. RESULTS: During the median follow-up period of 19 (6–53) months, 29 (31.2%) patients developed at least one severe infection. Older age (adjusted hazard ratio [HR] = 2.02, 95% confidence interval [CI]: 1.14–3.52, per 10 years; P = 0.016), low BMI (< 18.5 kg/m(2) compared with normal BMI [18.5–23.0 kg/m(2)], adjusted HR = 2.63, 95% CI: 1.11–6.19; P = 0.027), and use of methylprednisolone pulse therapy (adjusted HR = 2.48, 95% CI: 1.07–5.76; P = 0.034) were found to be significant predictors of severe infection. CONCLUSIONS: Low BMI was associated with a higher risk of severe infection in older adults with MPA, suggesting that careful management may be required to prevent this complication in this vulnerable group. Further studies are needed to elucidate the optimal treatment strategy for these patients. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-021-02123-y.