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explain this finding. Additionally, it is also challenging to relate the increased prevalence of TB to the immune disturbances caused by the disease itself, which may also contribute to the risk of developing TB. This increased rate of TB has been observed previously in the early stages of disease in patients with SpA 6 and was expected to be present also in patients with longer disease duration (and longer exposure to inflammation), as in the current study (mean disease duration of 7.0 years). Previous studies in anti-TNF naïve RA patients have shown an increased risk of developing TB (ranging from a 4-fold to a 7-fold increase) compared with the general population 10, suggesting that uncontrolled and chronic inflammation predisposes to TB.
Although some studies have reported that the overall prevalence of TB is lower in women, plausible reasons to explain such a differential effect remain obscure. Factors such as differences in the progression from infection to clinically manifest disease, differences in immune system responsivity and biological differences in disease presentation may be part of the explanation 25. Although the incidence of TB in LA has declined in the last two decades, the region is still considered an endemic area for TB, mainly due to the presence of social factors that predispose to the disease 26. In general, these factors increase the exposure to TB-bacilli.
The risk of developing a malignancy was not significantly increased in SpA patients in comparison to the general population. This finding is consistent with previous studies reporting that the overall risk of malignancies was not significantly higher in AS and PsA patients, including those treated with DMARDs or TNF-inhibitors 27. While malignancies are not rare in patients with AS, there is not a biologically plausible reason to expect a higher risk of cancer in these patients 12.
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