Macrothrombocytopenia: Investigating the Ultrastructure of Platelets and Fibrin Networks Using Scanning and Transmission Electron Microscopy

Macrothrombocytopenia is a rare condition where large, circulating platelets ranging between approximately 5 and 20 microm are found (typically platelets size range from 1.5 to 2.5 microm). The condition is also characterized by the prevalence of decreased numbers of circulating platelets, bleeding, short circulating times in blood, as well as abnormal platelet destruction. The current research investigates the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of platelet aggregates and fibrin networks of a family diagnosed with macrothrombocytopenia. Although TEM analysis of macrothrombocytopenia is not novel, little is known regarding the SEM analysis of platelet aggregates and fibrin networks. Here the authors show that macrothrombocytopenia have two different variations of giant platelet aggregates: a bulbous, giant aggregate that is very similar to control aggregates, and a giant flattened aggregate, with a compressed outer rim and a centrally placed area that forms a bulbous pseudopodia-like core. TEM micrographs of controls showed that, as previously seen in the literature, an aggregate contains dense bodies and alpha granules that carry, among other compounds, fibrinogen. TEM micrographs of the individuals with macrothrombocytopenia revealed aggregates with large vacuoles and areas mostly devoid of dense bodies and alpha granules. An interesting observation was that, in the presence of added human thrombin (to initially form the clot), fibrin fiber networks, comparable to that of control fibrin networks, were formed. This might be of clinical interest in the treatment regime and should be investigated further.