Thrombosis (Blood Clots)

Thrombosis is a blood clot that develops within veins or sometimes arteries in the body. Thrombosis may be serious or inconvenient but often occurs as a complication of a procedure, medication, or other disease. If left untreated a thrombosis can cause long-term problems; such as chronic swelling, pain, or even permanent damage to internal organs.

Thrombophilia refers to anything that increases one’s tendency to develop blood clots. Thrombosis in children is uncommon and is most often seen in children with complex medical problems or procedures. Thrombophilia can be considered the opposite of hemophilia, a disorder that prevents blood from clotting.

Thrombophilia refers to a group of disorders that increases a child’s tendency to develop dangerous blood clots. There are two main types of thrombophilia:

• Inherited thrombophilia is caused by certain genetic conditions.
• Acquired thrombophilia is caused by lifestyle factors or medical conditions, including immobility, obesity, sedentary lifestyle, trauma, smoking, or oral contraceptive use.

Thrombosis symptoms in children can vary significantly depending on the size and location of the blood clot, and each child may experience symptoms differently. A thrombosis may occur anywhere in a child’s body, but most are in the legs or arms (deep-vein thrombosis or DVT) or lungs (pulmonary embolism). Other types of thrombosis include sinus venous thrombosis and arterial thrombosis.

Children with a thrombosis in the legs or arms may have the following symptoms:

• Swelling
• Pain
• Redness and warmth
• Low-grade fever
• In some cases, you may even be able feel the clot, like a knot or rope under the skin

If a child has a pulmonary embolism, they may experience:

• Chest pain
• Shortness of breath, often beginning suddenly

A pulmonary embolus is a life-threatening medical emergency, and you should seek help immediately if you suspect this condition in your child.

It is important to understand that some thrombosis symptoms may resemble those of other more common medical problems. Because some of these symptoms can also point to other conditions, it’s important to have your child evaluated by a qualified medical professional for an accurate diagnosis and prompt treatment. If you have a family history of thrombosis, it is important to bring this up during evaluation for these symptoms.

There are three categories of causes of thrombosis: damage to the blood vessel (catheter or surgery), slowed blood flow (immobility), and/or thrombophilia (if the blood itself is more likely to clot).

Causes of thrombosis depend on whether your child has inherited or acquired thrombosis. Inherited thrombophilia is caused by certain genetic conditions while acquired thrombophilia is caused by lifestyle factors or medical conditions.

Possible factors for acquired thrombophilia include:

• Immobility
• Obesity
• Sedentary lifestyle
• Trauma

In teens and adults, risk factors also may include smoking or oral contraceptive use. Some patients with chronic inflammation or rheumatologic disorders may develop antiphospholipid antibody syndrome, a disorder where antibodies produced by the patient cause thrombosis to occur.

The first step in treating your child is forming an accurate and complete diagnosis. If thrombosis is suspected, imaging is done to confirm the diagnosis and to define where the blood clot starts and ends. Thrombosis is sometimes found accidentally but mostly because patients develop signs and symptoms of a blood clot.

If your child is suspected of having a thrombosis, diagnostic tests may include:

• A physical examination to evaluate symptoms of a blood clot
• Ultrasound, an imaging technique that uses high frequency sound waves and their echoes to make images of the inside of your child's body
• Magnetic resonance imaging (MRI), an imaging exam that uses a large magnet, radio waves, and a computer to produce two- and three-dimensional images of your child's body's organs, tissues, and bones
• Computed tomography (CT or CAT) scan, a non-invasive procedure that uses X-ray equipment and computers to create detailed, cross-sectional images of your child's body
• Analysis of blood samples to evaluate whether your child’s blood is clotting normally and identify any abnormalities in the levels of certain proteins
• Genetic tests may be performed to check for hereditary disorders (inherited thrombophilia)

There may be other diagnostic tests your doctor will discuss with you depending on your child's individual situation. After we complete all necessary tests, our experts meet to review and discuss what they have learned about your child's condition. Then we will meet with you and your family to discuss the results and outline the best possible treatment options.

Your child’s treatment team will determine a specific care plan. In most cases, thrombosis is treated with anticoagulation medications (blood thinners). These medications prevent the clot from growing and decrease the risk of its breaking apart and causing further complications. Your child may need to continue taking these medications for several months after initial treatment.

Examples of anticoagulation medication your child’s physician may prescribe include:

• Injections under the skin (also called subcutaneous injections) of a low molecular weight heparin such as enoxaparin (Lovenox) or dalteparin (Fragmin)
• Oral agents such as warfarin (Coumadin)
• Intravenous heparin
• Antiplatelet agents such as aspirin, clopidogrel (Plavix), or prasugrel (Effient)

Other treatments may include wearing compression stockings, remaining active, and applying warm packs to improve blood flow and pain caused by the clot.

Of course, your child's team of doctors will help determine the best approach for your child's unique situation, based on a number of factors, including:

• Your child's age, overall health, and medical history
• The severity of the disease
• Your child's tolerance for certain medications, procedures, or therapies
• How your child's doctors expect the disease to progress
• Your opinion and preferences

Some deep vein thromboses may resolve without treatment. Treatment is given to help get rid of the blood clot and to minimize complications of thrombosis. If the blood clot remains, other veins will enlarge to bypass the blockage. Sometimes these veins are visible, like varicose veins. After a blood clot some people develop long-term pain and swelling in the leg called post-thrombotic syndrome, which is caused by reduced blood flow and damage to the affected vein. Some patients also have changes in skin color, which may not develop for a year or more afterward.

Blood clots in the thigh are more likely to break off and travel to the lungs than blood clots below the knee or in the arms. A pulmonary embolism can be a life-threatening emergency, requiring immediate medical attention.

Children and young adults with blood clots are treated through the Dana-Farber/Boston Children’s Thrombosis, Anticoagulation, and Vascular Patency Program. Through our unique program, we can quickly identify children who need anticoagulation medications (or “blood-thinners”) using established monitoring and risk identification guidelines. Children outside of the hospital visit our outpatient center staffed by pediatric hematologists and pediatric hematology nurse practitioners with specialized expertise in the diagnosis and treatment of thrombosis.

For many children with rare or hard-to-treat conditions, clinical trials provide new options. Participation in any clinical trial is completely voluntary. We will take care to fully explain all elements of the treatment plan prior to the start of the trial, and you may remove your child from the medical study at any time. Currently, our hematology team is studying several new oral blood thinners in children for treatment and prevention of blood clots. We are also involved in an international study of the length of anticoagulation needed to treat thrombosis. Your hematologist may mention opportunities to participate in these studies, but you should feel free to ask about current research studies relevant to your child.

Researchers at Dana-Farber/Boston Children’s perform scientific and clinical research on platelets and related aspects of hemostasis and thrombosis. A particular focus is antiplatelet therapy, including the characterization of:

• How newly discovered molecules and mechanisms could help control platelets and clotting
• How antiplatelet drugs affect normal blood clotting (coagulation) and aspects of the immune system (e.g., inflammation)
• The relationship between the strength of antiplatelet treatments and the balance between thrombosis (uncontrolled clotting) and hemorrhage (uncontrolled bleeding)
• How tests of platelet function could help guide antiplatelet therapy in the clinic