Enhanced in vivo platelet activation in subtypes of ischemic stroke

It remains uncertain whether platelet activation in ischemic stroke is contributory or secondary to brain ischemia. The efficacy of aspirin (ASA) in stroke prevention suggests that platelet activation contributes to the occurrence of stroke. On the other hand, platelet activation may be simply a generalized consequence of cerebral ischemic damage. To examine this issue, plasma levels of the platelet specific proteins β-thromboglobulin (β-TG)and platelet factor 4 (PF₄) were measured in fifty-eight patients with various defined types of acute ischemic strokes. β-TG was a broader indicator of platelet activation than PF4. Compared with an age-matched control group, thromboembolic and cardioembolic stroke patients had significantly elevated β-TG levels (p < 0.001). Also, β-TG levels in these stroke categories were significantly higher in samples drawn within the first week after the event than in those drawn later (p < 0.001). In contrast, β-TG levels in lacunar stroke patients and in most TIA patients were normal. β-TGlevels did not correlate with the volume of cerebral infarction as measured by planimetry from CT scans. Moreover, β-TG levels in patients on chronic ASA therapy at the time of stroke did not differ from those in patients of the same diagnostic categories not taking aspirin. These data indicate that platelet activation may be important in some, but not all, subtypes of ischemic stroke and that platelet activation can occur in stroke even though the platelet cyclooxygenase pathway is suppressed.