Many patients with thrombocytosis experience no symptoms. When symptoms do manifest, the most common signs include bleeding from various sites, such as the nose, mouth, gums, or gastrointestinal tract. Furthermore, abnormal blood clotting can lead to serious complications like stroke, heart attack, and unusual clots in abdominal blood vessels. In certain cases, particularly with essential thrombocythemia, patients may develop erythromelalgia, characterized by redness, pain, swelling, numbness, and tingling in the hands and feet.