The disease is caused by overgrowth of a blood cell precursor, and is a type of slowly-progressive, or chronic, malignancy. Although the platelets are primarily affected, the red blood cells and white blood cells are also involved.

The disease has similarities to polycythemia vera, chronic myelogenous leukemia, and myelofibrosis. Usually it affects people in middle age. Bleeding can occur from the gastrointestinal, respiratory, urinary tract, or skin.

The formation of blood clots, called thrombosis, may coincide with bleeding episodes. It may even cause strokes in some people. Risk factors are unknown. The incidence is about 3 out of 100,000 people.

• Nosebleeds (epistaxis)
• Bleeding from the gums
• Bleeding from the gastrointestinal tract
• Easy bruising
• Prolonged bleeding from surgical procedures or tooth extraction
• Enlarged lymph nodes (rare)
• Stools, bloody
• Headache
• Numbness of hands or feet
• Dizziness
• Ulcers on fingers or toes

• Bone marrow aspiration.
• CBC that shows elevated platelet count.
• Uric acid level may be elevated.
• Physical examination may show enlarged spleen or liver.

If a patient is having life-threatening complications, rapid decrease of the platelet count may be achieved through platelet pheresis, a procedure to remove platelets from the blood directly.

Long-term decrease of the platelet count using medications can reduce both bleeding and clotting complications. Most common medications include hydroxyurea, interferon-alpha, or anagrelide. For patients with a known clotting tendency, aspirin may help decrease clotting episodes.

• Severe hemorrhage
• Thrombotic episodes (stroke, heart attack, or blood clots in extremities)
• Acute leukemia or myelofibrosis can develop in some patients

• If unexplained or prolonged bleeding occurs.
• If chest pain, leg pain, confusion, weakness, numbness, or other new symptoms develop.