Essential thrombocythemia is a condition characterized by an increased number of platelets (thrombocythemia). Platelets (thrombocytes) are blood cell fragments involved in blood clotting. While some people with this condition have no symptoms, others develop problems associated with the excess platelets.Abnormal blood clotting (thrombosis) is common in people with essential thrombocythemia and causes many signs and symptoms of this condition.Clots that block blood flow to the brain can cause strokes or temporary stroke-like episodes known as transient ischemic attacks.hile some people with this condition have no symptoms, others develop problems associated with the excess platelets. Abnormal blood clotting (thrombosis) is common in people with essential thrombocythemia and causes many signs and symptoms of this condition.