Increasing proportion of female patients with ankylosing spondylitis: a population-based study of trends in the incidence and prevalence of AS

OBJECTIVE: With the introduction of MRI in diagnosis and tumour necrosis factor inhibitors for treatment, the field of ankylosing spondylitis (AS) has undergone significant changes. We carried out a population-based study of the trends in incidence and prevalence of AS over the past 15 years. METHODS: This is a retrospective analysis of provincial health administrative databases. Residents of Ontario, Canada aged 15 years or older diagnosed with AS between 1995 and 2010 were included in the study. Crude as well as age-standardised and sex-standardised incidence and prevalence of AS between 1995 and 2010 were calculated. Trends in prevalence and incidence of male and female patients with AS were separately analysed. RESULTS: We identified 24,976 Ontarians with AS. Age/sex-standardised AS prevalence increased from 79/100,000 in 1995 to 213/100,000 in 2010. Men had higher prevalence than women, but the male/female prevalence ratio decreased from 1.70 in 1995 to 1.21 by 2010. A higher proportion of male compared with female patients with AS were diagnosed in the 15-45 age group. Annual incidence rates revealed increasing diagnosis of AS among women after 2003. CONCLUSIONS: The prevalence of AS in Ontario has nearly tripled over the past two decades. The proportion of women with new diagnosis of AS is increasing, a trend that began around the year 2003. A higher proportion of male compared with female patients with AS are diagnosed at an earlier age.