Laboratory monitoring of Scott Syndrome


inline image

A 66-year-old woman with Scott Syndrome presented with a sudden loss of vision in the left eye. Ophthalmological review confirmed a diagnosis of intravitreal haemorrhage. It was not possible to visualize the retina at this stage but later the bleeding was shown to be secondary to a retinal artery thrombosis. She was treated with oral tranexamic acid 25 mg/kg tds and was transfused a single pool of platelets (approximately 240 × 109 platelets). On the second day of admission there was no discernable improvement. In order to obtain an objective measure of response to platelet transfusion, a platelet-rich plasma (PRP) thrombin generation assay was performed as previously described by Lewis et al (2007). Peripheral blood samples were obtained before and 30 min after the transfusion of a single pool of platelets. The sample taken pre-transfusion showed a markedly reduced thrombin generation in PRP and, as expected, normal thrombin generation in platelet poor plasma (PPP). The post-transfusion sample showed a partial normalization of thrombin generation in PRP but was still abnormal compared to PPP. That evening the patient’s symptoms worsened and therefore she received a second pool of platelets. The following day the thrombin generation in PRP was repeated before and after the transfusion of two pools of platelets. The post-transfusion sample showed better correction of thrombin generation approaching that in PPP. Thereafter the patient received 2 pools of platelets and tranexamic acid daily until discharged, during which time there was a slow improvement in vision of the affected eye. She has subsequently had laser surgery under platelet cover without excess bleeding.

Scott syndrome is a rare platelet function disorder characterized by decreased externalization of negatively charged phospholipid on the platelet membrane. This results in reduced binding of coagulation factors to the platelet surface and decreased tenase and prothrombinase activity on the platelet surface. As demonstrated in this patient, this results in diminished thrombin generation in PRP. By transfusing normal donor platelets the deficit in thrombin generation can be reduced and treatment tailored to the clinical situation. It has been suggested that measurement of thrombin generation may help to individualize haemostatic treatment for patients. This case provides an example of how this concept might be put into clinical practice.