Acute thrombocytopenia in patients treated with amiodarone is caused by antibodies specific for platelet membrane glycoproteins.

Amiodarone has been implicated as a cause of thrombocytopenia but the responsible mechanism is unknown. We performed studies in three patients to characterize the pathogenesis of this complication. No amiodarone-dependent, platelet-reactive antibodies were identified using conventional serological techniques.

Thrombopoietin levels in patients with disorders of platelet production: diagnostic potential and utility in predicting response to TPO receptor agonists.

Thrombopoietin (TPO) is the major regulator of megakaryopoiesis. Measurement of serum TPO levels may help distinguish between various causes of thrombocytopenia and predict treatment response to TPO receptor agonists. Serum TPO levels from 118 healthy volunteers and 88 patients with abnormal platelet counts were measured using a quantitative ELISA assay.

Asymptomatic factor VII deficiency: gene analysis and structure-function relationships.

Factor VII Padua is a variant form of factor VII deficiency characterized by a prolongation of the prothrombin time (PT), when the assay is performed using rabbit brain thromboplastin. The PT is normal when performed using either human or ox brain thromboplastin reagents, or a recombinant human tissue factor-based thromboplastin. We report a case of an African-American woman with asymptomatic factor VII deficiency, who had a prolonged PT and factor VII activity levels of 5-8% using rabbit brain thromboplastin, but a normal PT and factor VII activity levels when measured using recombinant human brain thromboplastin or tissue factor.

Rosiglitazone-induced immune thrombocytopenia.

Rosiglitazone is one of the members in the thiazolidinedione (TZD) class of anti-diabetic agents that have proven efficacy in the treatment of patients with type 2 diabetes. We studied serum from a patient who developed acute, severe thrombocytopenia after exposure to rosiglitazone maleate (Avandia) and proposed the mechanisms for rosiglitazone-induced thrombocytopenia. Tested by flow cytometry, the patient's serum was positive for rosiglitazone-induced antibody with the binding ratio of 5.

Association of C807T, Pl(A), and -5 C/T Kozak genotypes with density of glycoprotein receptors on platelet surface.

This study investigates whether three platelet glycoprotein (GP) polymorphisms, C807T in GP Ia, Pl(A1/A2) in GP IIIa, and -5 T/C Kozak in GP Ibalpha gene, influence the density of the three important adhesion and activation receptors on the platelet surface. Fifty-four healthy donors were genotyped according to the three polymorphisms, and densities of the corresponding GPs were measured by flow cytometry. Our study confirmed the association between C807T polymorphism and platelet surface expression of GP Ia-IIa and GP Ia and demonstrated that the density of GP Ibalpha or GP IX is not associated with the Kozak polymorphism.

Glycoprotein IIb/IIIa complex is the target in mirtazapine-induced immune thrombocytopenia.

Mirtazapine (MW 265.36), a tetracyclic antidepressant of the piperazine-azapine group which augments central noradrenergic and serotonergic activity, is currently used as an oral antidepressant. We report a case of severe thrombocytopenia in a 66-year-old patient occurring after mirtazapine administration, suggesting an immune mechanism.

von Willebrand factor-cleaving protease inhibitor in a patient with human immunodeficiency syndrome-associated thrombotic thrombocytopenic purpura.

Antibodies that inhibit von Willebrand Factor (VWF)-cleaving protease activity occur in patients with acute thrombotic thrombocytopenic purpura (TTP) and often persist in the chronic phase. A deficiency of this protease is likely to be responsible for the generation of ultrahigh VWF multimers and influence the formation of intra-arterial platelet aggregates that result in microangiopathic haemolytic anaemia, thrombocytopenia and end in organ failure. This report demonstrates complete deficiency of VWF-cleaving protease and the presence of a concentration-dependent IgG1 inhibitor in the plasma of a patient with acquired immunodeficiency syndrome (AIDS).

Differential diagnosis of platelet dysfunction.

These discussions are selected from the weekly staff conferences in the Department of Medicine, University of California at San Francisco. Taken from transcriptions, they are prepared by Drs. Martin J.