Myeloproliferative neoplasms are diseases characterized by excessive proliferation of myeloid cells in the bone marrow. Essential thrombocythemia (ET) is a myeloproliferative neoplasm that causes platelet proliferation. Although the prognosis for ET has improved because of cytoreductive therapies, some patients can still experience complications including bone marrow fibrosis or acquired von Willebrand disease. A 79-year-old man with a history of hyperthrombocytosis was admitted for rehabilitation after prolonged hospitalization. His treatment included hydroxyurea, which was discontinued because of side effects, and anagrelide, which was unsuccessful in controlling his platelet count. The patient showed generalized convulsions and psychiatric symptoms such as irritability. Based on his clinical symptoms and electroencephalography, he was diagnosed with peri-seizure psychiatric symptoms. Lacosamide was administered to control the seizures. He eventually died of hemorrhagic shock because of ET. However, appropriate epilepsy care improved his psychiatric symptoms and quality of life. The patient was classified as having ET with a high risk of both thrombosis and a poor prognosis because of his age, history of thrombosis, elevated white blood cell count, and JAK2 mutation. In epilepsy care, both convulsive seizures and psychiatric symptoms are important therapeutic targets. Lacosamide, which can be administered orally or intravenously and has a low risk of side effects, was chosen for the present patient. There have been no reports of epileptic seizures associated with ET in palliative medicine. Therefore, this case report is novel and useful for psychiatrists engaged in palliative care medicine and liaison consultation psychiatry.