Acquired thrombasthenia due to inhibitory effect of glycoprotein Iibiia autoantibodies

Background: A 75 year old patient presenting with mucocutaneous bleeding was diagnosed with acquired thrombasthenia. The diagnosis was based on lack of platelet aggregation with adenosine diphosphate (ADP), arachidonic acid and collagen, and normal aggregation induced by ristocetin. Objective: To study the mechanism of platelet function inhibition in a patient with acquired thrombasthenia. Methods: Aggregation assays of platelets from the patient and healthy controls were performed. In addition, antiglycoprotein (GP) IIbIIIa antibodies binding to normal platelets in the presence or absence of the patient's serum was studied by flow cytometry. Results: Aggregation of normal platelets in the presence of patient's plasma was inhibited four- and 2.5-fold in the presence of ADP and arachidonic acid respectively, while collagen-induced aggregation was completely abolished. Ristocetin-induced aggregation was normal. The patient's serum inhibited binding of commercial anti-glycoprotein IIbIIIa antibodies to normal platelets twofold by flow cytometry. Treatment with anti-CD20 monoclonal antibody (rituximab) normalized the patient's platelet aggregation. Conclusions: These results suggest that the patient developed inhibitory anti-GPIIbIIIa autoantibodies that caused acquired thrombasthenia.