Background/Purpose: To determine trends in the incidence and clinical presentation of ankylosing spondylitis (AS) among residents of a geographically defined area first diagnosed 1980-2009 and to describe survival among these patients.

Methods: A population-based inception cohort of patients with AS was assembled by screening all medical records of residents of a geographical area with any diagnosis consistent with AS. We identified residents aged 18 years or older first diagnosed between January 1, 1980 and December 31, 2009. Cases were included if they fulfilled the modified New York criteria for AS or the ASAS criteria for axial spondyloarthritis and the date at which the criteria was fulfilled was considered the date of diagnosis.  Incidence rates were estimated and were age- and sex-adjusted to the 2000 US white population. All identified cases were followed until death, migration or December 31, 2011. Cases with psoriasis, inflammatory bowel disease (IBD) and reactive arthritis were identified. Survival was estimated using the Kaplan-Meier method and compared to expected survival for persons of the same age, sex and calendar year estimated using US population life tables.

Results: 95 patients were newly diagnosed with AS between 1980-2009 (25 women and 72 men) based on ASAS criteria for axial spondyloarthritis. 92 (97%) patients met modified New York criteria. The overall age and sex-adjusted incidence for AS was 3.9 per 100,000 population (95% CI 3.1, 4.6). The age- adjusted incidence in men was more than three times that of women: 6.0 (95% CI 4.6, 7.4) vs 1.8 (95% CI (1.0, 2.5) per 100,000 population. The mean age at diagnosis was 35 years (min: 18 max: 69). Patients diagnosed in the 1990s (mean 39 years) were older than those diagnosed in the 1980s (mean 32 years) or the 2000s (mean 34 years).  The median interval between symptom onset and diagnosis was 4.0 years (min: 0, max: 36 years) with no significant difference over the study period (p = 0.539).  The incidence of AS was highest in the 25-34 age group at 8.0 per 100,000. Of 75 patients tested for HLA-B27 antigen, 65 (87%) were positive. Inflammatory back pain was the most common presenting manifestation and was seen in 92% of patients. Twenty nine patients (32%) had peripheral arthritis at diagnosis which was more common in patients diagnosed in the 1990s (50%) compared to the 1980s (36%) or the 2000s (20%; p=0.034). Ten patients (11%) also had psoriasis and 10 (11%) had IBD. Uveitis was the most common extra-articular manifestation, seen in 31 patients (33%) with no significant change over the study period (p=0.22). Uveitis occurred more often in women (56% vs 25%; p=0.005). There were 3 deaths during a median follow up duration of 8.5 yrs. (total 998 person-years). This was consistent with the 4.4 expected deaths (standardized mortality ratio: 0.68; 95% CI 0.14, 2.00).

Conclusion: AS occurs in about 4 persons per 100,000 per year. Patients diagnosed in the 1990s had more peripheral arthritis and were slightly older at diagnosis than patients in any other decade. Clinical features, extra-articular manifestations and interval from symptom onset to diagnosis have remained constant in this population over the study period.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/trends-in-incidence-and-clinical-features-of-ankylosing-spondylitis-in-olmsted-county-1980-2009-a-population-based-study/