Graves' disease presenting with extreme thrombocytosis associated with exacerbation of hyperthyroidism: A case report

Immune thrombocytopenia is associated with autoimmune thyroid diseases, including Graves’ disease and Hashimoto’s thyroiditis. Conversely, cases of thyroid disease accompanied by thrombocytosis have rarely been reported. We describe herein an extremely rare case of Graves’ disease in which the platelet count increased markedly following exacerbation of hyperthyroidism. The patient was a 76-year-old woman who had been diagnosed with Graves’ disease at 28 years old. Her thyroid function had been maintained within the normal range by administration of thiamazole (MMI). At 67 years old, platelet count had increased from around 200,000/μL to 1,551,000/μL, in association with exacerbation of hyperthyroidism. The results of bone marrow biopsy, genetic testing and chromosomal analysis revealed no evidence of myeloproliferative disorder. With increased doses of MMI, thyroid function rapidly normalized, and platelet counts decreased to 665,000/μL after two months and 447,000/μL after five months. However, mild thrombocytosis of around 400,000/μL persisted for two years, and six years was required for the platelet count to finally return to pre-increase levels. No complications associated with increased platelet counts, such as thrombosis, were observed during treatment. This is the first report of marked reactive thrombocytosis associated with exacerbation of Graves’ disease. It is also unclear why thrombocytosis persisted for a long period even after normalization of thyroid function, so careful observation of patient progress remains necessary.