Association Between Body Mass Index and Severe Infection in Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis: A Retrospective Cohort in Japan

Abstract 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 elderly AAV patients with a low BMI would be at a higher risk of infection. To evaluate this hypothesis, we investigated the association between underweight at AAV diagnosis and subsequent severe infection in elderly AAV patients.Methods: This single-center retrospective cohort study included 98 consecutive elderly AAV patients 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.Results: During the entire follow-up period (median, 22 months; interquartile range, 7‒52 months), 32 (32.7%) patients developed at least one severe infection. Low BMI (< 18.5 kg/m2 compared with normal BMI [18.5‒23.0 kg/m2], adjusted hazard ratio [HR] = 2.70, 95% confidence interval [CI]: 1.18–6.17; P = 0.018) and use of methylprednisolone pulse therapy (adjusted HR = 3.09, 95% CI: 1.37–6.99; P = 0.007) were the significant predictors of severe infection. Furthermore, an interaction effect between unintentional body weight loss (> 10%) within 6 months before diagnosis and low BMI was observed (P < 0.001).Conclusions: Low BMI was associated with a higher risk of severe infection in elderly AAV patients, suggesting that careful management may be required to prevent the development of infection in patients with a low BMI. Further studies are needed to elucidate the optimal treatment strategy for these patients.