Mortality in osteoarthritis patients consulting health care

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Purpose: Metabolic factors such as obesity play a role in the etiology of osteoarthritis. A connection between osteoarthritis (OA), metabolical syndrome and subsequently mortality has been suggested. Evidence concerning mortality has unfortunately been controversial, we therefore sought to examine the occurrence of mortality in our OA cohorts. Methods: 384 patients were included in the ‘Genetics ARthrosis and Progression’ (GARP) study, a prospective longitudinal cohort, with symptomatic OA at multiple sites in the hand or in at least 2 of the following sites: hand, knee, hip or spine. Patients consulted rheumatologists, orthopedic surgeons or general practitioners and underwent baseline assessment between August 2000 and March 2003. For the replication analysis, we studied 460 patients who consulted the rheumatology outpatient clinic and the clinical nurse specialist. They were consecutively included in the ‘Zorgpad artrose’ cohort between August 2005 and April 2009 and were diagnosed by the rheumatologist with primary hand, knee or hip OA. All subjects were followed until 2 November 2011. Mortality was compared between included patients with OA and the general population in the Netherlands, matched for both age and gender. For GARP, the expected numbers of deaths came from age and gender specific mortality data provided in the mortality statistics from 2006 in 5-year age bands and for ‘Zorgpad artrose’ the data came from 2009. Standardized Mortality Ratios (SMR) with 95% confidence intervals (95% CI) were calculated using STATA (version 10.1). Results: The GARP study consisted of 384 participants (82% women) and the mean age at inclusion was 60.1 (range 42-79). The duration of follow-up was 9.0 (SD 1.2). No excess mortality was observed in OA patients when compared to the general population. 26 patients died, while the expected number of deaths was 48 (SMR 0.54, 95% CI 0.37 - 0.79). The SMR was 0.47 (0.29 - 0.76) in women and 0.73 (0.39 - 1.35) in men. Healthy cohort effect was also tested and not likely present. In our replication cohort we found similar results (11 patients died, SMR 0.45, 95% CI 0.25 - 0.82). The SMR was also lower in women (0.40, 0.20 - 0.81) than in men (0.66, 0.21 - 2.06) Conclusions: In patients consulting health care, OA does not lead to a higher mortality rate in women and a similar trend can be observed in men. These results do not support the hypothesis that metabolic syndrome is an important cause of OA and would influence the mortality of patients consulting primary or secondary health care for their complaints. Whether this is due to selection of patients or reflects a true absence of metabolic syndrome in OA has to be further investigated.