Essential Thrombocythemia, Acquired von Willebrand Disease, and Acquired Pernicious Anemia: A Case of Potential Beneficial Autoimmunity.

Essential thrombocythemia (ET) is a myeloproliferative neoplasm characterized by elevated platelet counts and risks of both thrombosis and bleeding. Acquired von Willebrand disease is a rare complication of ET, particularly in extreme thrombocytosis. We report a 32-year-old man diagnosed with ET, acquired von Willebrand disease, and autoimmune gastritis with vitamin B12 deficiency. He presented with marked thrombocytosis (1,340 × 109/L), reduced von Willebrand factor activity, low vitamin B12 levels, and positive parietal cell antibodies, but remained asymptomatic. The coexistence of these 3 conditions is rarely reported and may represent a form of beneficial autoimmunity, in which autoimmune phenomena paradoxically confer protective effects against thrombotic complications.