Background--Essential thrombocythemia (ET) is a chronic myeloproliferative disorder with increased frequency of thrombotic events, including transient ischemic attacks (TIAs) and stroke. Moyamoya syndrome is a rare cerebrovascular disease characterized by progressive occlusion of intracerebral arteries with a typical "puff of smoke" angiographic pattern. We report the development of moyamoya syndrome in a patient with ET.

Case Description--The patient is an 18-year-old female who presented at age 13 with recurrent TIAs. Persistent thrombocytosis was found, a diagnosis of ET was made, and treatment with anagrelide was started. Despite normal platelet counts, she experienced recurrent TIAs and stroke. Severe stenosis of the supraclinoid segment of the left internal carotid artery (LICA) and abnormal collateral vessels were found, and moyamoya syndrome was diagnosed on the basis of the characteristic angiographic appearance. An intracranial stent was placed in the LICA, and since then, she has had an uneventful outcome after a 46-month follow-up.

Conclusion--To our knowledge, the development of moyamoya phenomenon has not been reported in ET, and the relationship between these 2 disorders remains unclear. Besides, this is the first intracranial carotid stent implanted successfully in a patient with moyamoya.