INTRODUCTION
Idiopathic thrombocytopenic purpura (ITP) is a blood disorder characterized by immune-mediated antibody platelet destruction1,2 . ITP is categorized into primary, or idiopathic, and secondary if a cause is identified such as a preceding viral illness or an underlying immunodeficiency3. The incidence rate of 1-6.4 cases per 100,000 children shows a biphasic age distribution: toddlers and adolescents4. The result is a quantitative platelet deficiency available for primary hemostasis manifesting as mucocutaneous bleeding (e.g., petechiae, bruising, oral/buccal purpura, epistaxis). Severe presentations including internal bleeding are rare in children and occur less frequently than in adults5.
A comparative prospective registry of 1,784 children newly diagnosed with ITP reported the incidence of joint bleeding involvement as the lowest of all organ systems6. Factors predictive for severe bleeding include severe thrombocytopenia (platelet count < 20 x 10*3/uL, Ref. range and units: 142 – 508 x 10*3/uL), newly diagnosed ITP, and previous minor bleeding6. Hemarthrosis is defined as bleeding into a joint and can cause monoarticular swelling and pain. The most common cause is trauma where bleeding develops due to bone, soft tissue, or ligamentous injury. Non-traumatic etiologies include bleeding disorders, osteoarthritis, septic arthritis, bursitis, intra-articular vascular anomalies or tumors such as synovial hemangiomas7,8,9. While prevalence rates of hemarthrosis in children with severe hemophilia A or B can be as high as 33-47%10, acute hemarthrosis in children without hemophilia is rare and typically follows traumatic injury8. While imaging findings can be suggestive, definitive diagnosis is via arthrocentesis for synovial fluid analysis. We present a case of non-traumatic hemarthrosis in the setting of ITP where the patient was found to have positive serologies for Lyme Disease.
Lyme Disease was first described as an arthritis in children that could be monoarticular or oligoarticular. Typical presentation occurs in stages with localized skin lesions followed by disseminated infection days to weeks later with migratory joint pain11. Without antibiotic treatment, 60% of patients with Lyme Disease develop arthritis involving one or many joints12. Progression to arthritis is a late disease manifestation resulting from strains of Borrelia burgdorferi disseminating into the joint space causing immune response with resultant inflammation12. Following antibiotics, spirochetes are destroyed, and inflammation of the affected joints typically resolves12.