The focus of this study on patients with longstanding disease gives an advantage in terms of reducing the confounding influence of large differences in AS duration, by examining patients at a time when the course of their AS had largely been established. However, a limitation is that the results are conditional on the fact that these are all patients with longstanding AS, and their results may not necessarily be generalisable to patients with early AS. In addition, this cohort is a convenience sample and is not community‐based, and thus may not represent the entire AS community.
The review of earlier studies showed that women had more peripheral arthritis and fewer spinal radiographic changes. However, a number of problems with methodological issues limits the conclusions that can be drawn from those studies. In our study, we found differences in usage of intra‐articular steroids, sulphasalazine and prednisone, which could suggest more peripheral arthritis in women with AS. Alternatively, these women with AS may have presented with peripheral arthritis and been considered to have a primary peripheral arthritis before AS was apparent or diagnosed. Our finding that more women with AS had positive family histories of AS could suggest that the diagnosis of AS may be made more often in women when suspicion for AS is heightened.
Although our study confirms the earlier finding that men have more radiographic damage than women, it also allows us to be more nuanced than the earlier studies in that our data show that women have more functional limitations for a given level of radiographic damage. There seemed to be an apparent contradiction in that although the radiographic outcome was significantly different between men and women, the functional outcomes were the same. However, an analysis of the associations of BASRI‐spine scores with functional measures in men and women showed that radiographic damage has a similar correlation with functional impairment in both men and women. Additional analyses of associations of men and women with functional measures after adjusting for BASRI‐spine scores showed that, for a given degree of radiographic damage, women reported more functional limitations.
Gran et al
showed that there were no differences between men and women with AS in terms of spinal mobility.1
Another study of patients with AS found that the changes in spinal mobility do not explain the observed differences in function.33
In addition, the relationship between the accumulation of spinal radiographic damage and corresponding function in AS remains unknown. Even among the studies in rheumatoid arthritis that have examined this issue more extensively, the nature of the connection between radiographic damage and functional loss is controversial and may differ over the time course of the disease.34,35,36
This discrepancy between radiographic damage and reporting of function may be a result of women having more peripheral arthritis. For example, patients with lower extremity (ie, knee) problems would be more likely to have lower function scores.37
The underlying pathogenesis of the differences between men and women with AS is unknown. The prevalence of HLA B27 among women with AS is equivalent to that in men,3
and no linkage of the X chromosome with susceptibility to AS was found.38,39
However, a direct genetic difference in the ankylosis homologue (ANKH) gene between men and women with AS has been recently described by Tsui et al
Further genetic studies may reveal more genes that are involved in the prevalence and severity of AS.
In conclusion, there are differences in the expression of AS between the genders. We observed that, among patients with longstanding AS, there are treatment differences between the genders that suggest that women may have more peripheral arthritis. Men have significantly more severe radiographic changes in spite of similar disease duration. We found that, at any given level of radiographic damage, women report worse functional outcomes. All of these findings suggest that the phenotype of AS differs between the genders, and this may influence the manner and timing of the diagnosis of AS as well as the choice and timing for initiation of treatment.