A patient with essential thrombocytosis and multiple sclerosis.

We report on a patient with a 5-year history of essential thrombocytosis (ET) who developed multiple sclerosis (MS) during the last 5 months. The patient was treated for MS with interferon-beta (IFN-beta), which also had a beneficial effect on the ET. We describe the patient's history and the beneficial effect of IFN-beta administration in reducing the number of platelets. We also discuss the possible link between the pathogenesis of ET and MS.