Working Diagnosis:
A working diagnosis was an acute superficial venous thrombosis (SVT) of the greater saphenous vein extending from below the knee to the foot secondary to thrombophilia from Factor V Leiden (FVL) mutation in the setting of trauma.

Treatment:
He was admitted for anticoagulation and started on enoxaparin but developed nausea and vomiting so was changed to rivaroxaban before discharge on day two. He was prohibited from participating in contact sports while on anticoagulation. The plan was to anticoagulate for twelve weeks and follow his clot progression with serial ultrasound studies.

Outcome:
His clot stabilized at six weeks, but he continued to show noncompressible clot burden. He stopped his therapy two weeks early to play in a hockey tournament and did not restart. An ultrasound at ten weeks showed a residual, occluding but stable clot in the greater saphenous vein. He had no bleeding complications from this therapy nor post-thrombotic syndrome. He was allowed to remain off therapy and has routine follow up with hematology in nine months for a repeat ultrasound. He was cleared for all sports.

Author's Comments:
The incidence of venous thromboembolism is 0.07-0.14 / 10,000 children. Risk factors include inherited thrombophilias, central venous devices, major trauma, malignancy, infection, surgery, immobility, nephrotic syndrome, congenital heart disease, inflammatory bowel disease, and chronic inflammatory disease. The incidence of venous thromboembolism peaks twice in childhood: during infancy and adolescence. Our patient's only risk factors were age and and factor V Leiden mutation in the setting of seemingly mild trauma. 5% of North American caucasians have at least one copy of factor V leiden. Heterozygosity increases the absolute lifetime risk for venous thromboembolism by three fold (Homozygosity by 50-80 fold). So, the relatively low risk for thrombosis in a healthy child who is factor V leiden heterozygote does not warrant the risk of lifetime prophylaxis. In summary, development of a venous thromboembolism in the setting of sports or other seemingly innocuous trauma should prompt a coagulopathy work-up.

Editor's Comments:
The vast majority of literature on thromboembolic disease in the pediatric population is on seriously ill children. Spontaneous thromboembolism is a rare event in the youth population with little dedicated research. However, risk factors for adults are generally recognized as risk factors for children and include: 1. Injury and endothelial damage, 2. Stasis, and 3. Hypercoagulability. These can occur in athletes due to underlying illness causing pro-inflammatory states,estrogen, malignancy, travel causing stasis, injury causing stasis, muscle hypertrophy, and congenital or acquired thrombophilias. High intensity exercise itself creates a transient hypercoagulable state and dehydration may also contribute to risk for a thromboembolic event. It is not known if athletes are more at risk for thromboembolic illness than the general youth population. While a rare event in athletes and young adults, an index of suspicion is important for extremity venous thromboembolism as it carries with it risk for both short and long term complications. Some risks include pulmonary embolism, risk for bleeding and other side effects of medication management, stroke, and post thrombosis syndrome. While not a study in athletes, one study found that over 80% of patients who had deep vein thrombosis had recurrent symptoms years later. There are currently recommendations published on return to play after thromboembolism in the adult population. Return to activity recommendations currently include starting with activities of daily living and progressing slowly and in a graduated manner back to allow for the clot to mature and stabilize. Return to contact sports is more complicated due to associated bleeding risks with anticoagulation therapy.
The significance of superficial thromboembolism is not well elucidated and there is little to no studies of superficial thromboembolism related to healthy children. Superficial venous thrombosis (SVT)typically presents with a palpable cord or firm area which follows the course of a superficial vein. The area may be hot or inflamed. SVT has similar risk factors as other types of thromboembolic disease listed above, however another significant risk factor is varicose veins. SVT was considered to be a benign self limiting condition, but, in recent years it has been found that it is occasionally associated with concurrent deep vein thrombosis or pulmonary embolus. It is also associated with an increased risk of these more severe thrombotic events within a year of presentation for SVT. More studies need to be done to determine the risk of severe complication from SVT in both the adult and pediatric population as well as the optimum treatment for SVT in various populations.
Factor V Leiden is a known risk factor for thrombosis. Factor V Leiden is reported to have an incidence of 5% in the North American caucasian population. Factor V is a pro-coagulant clotting factor. Factor V acts to increase the production of thrombin which is the enzyme that converts fibrinogen to fibrin which activates clot formation. Factor V Leiden is a mutated form of the Factor V protein that does not allow an inhibitory protein to bind leading to a hypercoagulable state. The condition is inherited in an autosomal dominant form with incomplete penetrance. The increased thrombotic events are typically limited to venous and there is also an increased risk of pre-eclampsia and fetal loss. Current treatment is to temporarily treat with anticoagulants after a thromboembolic event or in the times when the patient is considered to be high risk (examples include: for surgery or peri-partum). Life long anticoagulation therapy is not thought to be necessary.
Another complicating feature of management of thrombosis in the pediatric population is that anticoagulant therapies are not approved for use in children. While anticoagulation therapy is recommended by expert consensus at this time, it is recognized that bleeding risk and impact of anti-coagulation on quality of life is likely greater in children than older adults.

It is important for those who care for athletes to be aware of the the possibility of thrombosis in young athletes although these conditions are rare in this population. Hereditary thrombophilias, oral contraceptives, injury, and travel are risk factors that often may contribute to risk of thrombosis in this population. In an athlete who presents with leg pain or weakness, dyspnea, or shortness of breath, it is important to consider thrombosis. Often these diagnoses may be missed as athletic young people may not be labeled as higher risk based on algorithms created for an older and sedentary population and physical conditioning may mask some of the signs and symptoms. Young patients may present with subjective symptoms such as pain or relative exercise intolerance thus it is important for those who care for athletes to have a high index of suspicion and consider thrombosis when appropriate.

References:
1. Lucisano AC, et al. (2020). Trauma-Induced Coagulopathy in Children. Sem Thromb Hemost, 46:147-154.
2. Monagle P, et al. (2018). American Society of Hematology 2018 Guidelines for the Management of Venous Thromboembolism: Treatment of Pediatric Venous Thromboembolism. Blood Advances, 2(22): 3292-3316.
3. Goldenberg NE. (2019). Venous Thromboembolism in Children. Clin Advances Hem Onc, 17(6): 326-329.
4. Raffini L, et al. (2009). Dramatic Increase in Venous Thromboembolism in Children's Hospitals in the US from 2001-2008. Pediatrics, 124(4):1001-1008.
5. Jones S, Monagle P, Newall F. (2020). Do Asymptomatic Clots in Children Matter? Thrombosis Res, 189:24-34.
6. Carillo LA, et al. (2019). Venous Thromboembolism Risk Factors in a Pediatric Trauma Population. Ped Surg Internat. 35:487-493.

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