Secular trends in sickness absence among Swedish patients with ankylosing spondylitis and psoriatic arthritis

The aim was to investigate whether secular trends in sickness absence (SA) were present in patients with ankylosing spondylitis (AS) and psoriatic arthritis (PsA) receiving their diagnosis between 2002 and 2011. A repeated cross-sectional study design was used. Patients were identified in the Skane Healthcare Register (SHR). A washout period of 18 months was applied. The general population seeking health care was used as a reference cohort. SA data from 2003 to 2012 were obtained from the Swedish Social Insurance Agency and converted into net days of SA per year. Within diagnosis and sex, the average number of net days of SA during the calendar year following diagnosis was calculated and plotted against calendar year together with the corresponding SA of the age-standardized reference population. Linear regression on aggregated data, within diagnosis and sex, was applied to formally investigate differences in secular trends among patients and referents. There were 3173 patients and 992,502 referents. Among men diagnosed with AS, the average amount of SA declined by 8.1 net days per year in patients as compared with 2.4 in the referents (p = 0.01). Among PsA patients, the average amount of SA declined by 11.7 net days per year in women as compared with 2.7 in the referents (p < 0.001) and by 7.6 net days per year in men as compared with 1.9 in the referents (p < 0.001). Secular trends of declining SA were present among AS and PsA patients. Trends were also present among the referents, although not at all of the same magnitude.