89 Chapter 4 Discussion Bleeding tendencies have been occasionally reported in patients with OI, but detailed studies on coagulation defects in these patients are sparse. In this study we assessed the bleeding tendency with a validated questionnaire (ISTH-BAT) and investigated several laboratory parameters in all patients to identify or exclude a coagulopathy. The ISTH-BAT identified easy bruising in 74%. Five patients reported haemorrhages during surgery requiring blood transfusion and other medical interventions, such as a repeat surgery. These types of events have previously been reported in the literature in OI patients 9–14. Interestingly, 18% of the OI patients appeared to have an elevated BS but laboratory testing did not identify a coagulopathy. Intriguingly, three patients had test results that indicated hyperfibrinolysis (n = 2) and VWD type 1 (n = 1), but these patients did not have an elevated bleeding score and the two patients with hyperfibrinolysis did not report easy bruising. VWD type 1 has a high prevalence and is most likely unrelated to OI 28. For the patients with an elevated BS and no laboratory test abnormalities, it may be possible that the elevated BS is due to other causes. However, gender, age, OI type and the use of bisphosphonate did not point to a significant effect on bleeding tendency. Persiani et al. described a significantly higher rate of bleeding in OI type 3 patients who never used bisphosphonates and underwent femoral surgery 15. One hypothesis for this is that the reduction and/or abnormal production of collagen type 1 may predispose to capillary fragility, as the vessel walls contain collagen type 1 5,12,29. However, if this hypothesis would be true, one would expect an elevated BS in all patients with OI unless there is clinical variability, ranging from slight increased propensity to bruise in the patient, to more severe clinical features resulting in elevated BS. In this scenario, the underlying genetic cause may be an important factor. In two patients with a BS score of 0, moderately elevated fibrinolysis was measured by ROTEM®, which indicated an increased clot lysis that can lead to bleeding tendencies 30,31. Given that fibrinolytic activity depends upon the activity of endothelial cells, cellular elements of haemostasis may possibly play a role in triggering bleeding disorders 30. A suggestion for the possible connection between hyperfibrinolysis and OI could be a deficiency in plasminogen activator inhibitor-1 (PAI-1). PAI-1 deficiency has been reported in a patient with OI and spontaneous intraparenchymal haemorrhage 32. There is evidence that PAI-1 also has a role in bone formation in mouse models 33–35. PAI-1 is stabilized by vitronectin which is anchored to collagen type 1 36. As collagen type 1 production is reduced and/or abnormal this might influence a factor resulting in bleeding tendency in some OI
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