HISTORY: A 15 year-old high school linebacker sustained a direct blow to the right anterolateral shin during practice. The athlete had no apparent immediate injury and continued to practice. In the following hours, he developed a large bruise followed by swelling and dull pain in the right lower leg. There was no numbness, tingling, or weakness in the affected leg. The following day he was evaluated by his primary care physician. PHYSICAL EXAMINATION: Skin examination was remarkable for a 6cm x 8cm ecchymotic area (reddish-purple bruise) on the anterolateral aspect of the right shin. This area was minimally tender to palpation. There was also a fading bruise over the lower lumbar spine and numerous other small bruises in various stages of resolution on both arms and legs. There were no visible petechiae or purpura. There was no gingival bleeding or retinal hemorrhages. His abdomen was soft and nontender. The liver and spleen were not palpable. His extremity exam was significant for a left calf circumference of 36 cm, and a right calf circumference of 39.5 cm. His right calf was somewhat firmer than the left, but was not tender or tense. The distal extremities were well perfused. Range of motion and strength were normal. Sensation to light touch was intact and symmetrical. DIFFERENTIAL DIAGNOSIS: Traumatic hematoma Traumatic compartment syndrome Von Willebrand's disease Immune Thrombocytopenic Purpura Hemophilia TEST AND RESULTS: A CBC showed a white blood cell count of 11.1 with normal differential. His hemoglobin was 15.4 g/dl. The platelet count was markedly low at 10×103/ml (130–400× 103/ml). PT was slightly prolonged at 13.7 seconds (10–12 sec), INR was normal. Factor VIII, Von Willebrand Factor antigen, and VWF activity levels were all within normal limits. Antinuclear antibody (ANA) testing was negative. Bone marrow aspirate showed increased numbers of large, immature megakaryocytes, consistent with immune thrombocytopenic purpura. FINAL WORKING DIAGNOSIS: Immune (Idiopathic) Thrombocytopenic Purpura TREATMENT AND OUTCOMES: Oral steroids, high dose intravenous steroids, and intravenous immune globulin (IVIG) were minimally beneficial, and platelet counts remained low. Immunosuppressive therapy with 6-Merc apt op urine was successful in keeping platelets above 50×103/ml and was well tolerated by the patient. Weekly CBC's done the day prior to games. The athlete was allowed to participate in contact drills if weekly platelet count was greater than 50×103/ml. The athlete was prohibited from contact participation if platelet count was less than 50×103/ml and missed only one athletic contest as a result of low platelets.