[EDTA-dependent pseudothrombocytopenia in association with myasthenia gravis]

Ethylenediaminetetraacetate (EDTA)-dependent pseudothrombocytopenia, in vitro platelet clumping and consequent pseudothrombocytopenia in the presence of EDTA, was observed in a patient with thymoma-associated myasthenia gravis (MG). The patient, a 45-year-old man, presented with alopecia areata, and weakness and fatigue of right upper extremity and neck muscles. Diagnosis of MG was made on the basis of positive edrophonium test and antiacetylcholine receptor (AChR) antibody test. The platelet count was as low as 4.9 X 10(4)/mm3 in EDTA-anticoagulated blood and large agglutinates were seen in smears from EDTA blood. Platelet suspension immunofluorescence test showed IgG on the surface of platelet clumping. Corticosteroid therapy combined with thymectomy reduced the platelet clumping markedly in parallel with decrease of anti-AChR antibody titers. The present observation suggests that EDTA-dependent pseudothrombocytopenia in our patient was associated with some immunological abnormalities. Recognition of the pseudothrombocytopenia in MG patients is important to distinguish it from idiopathic thrombocytopenia purpura which is also found in MG and requires bone marrow tests and sometimes splenectomies.