RESULTS & CASE DESCRIPTION
A 7-year-old male presented with left knee swelling, generalized petechiae, and severe thrombocytopenia. The patient was previously healthy with no recent illnesses, medications, or trauma. Two weeks before presentation, he developed petechiae that progressed to cover his torso and extremities. Three days before presentation, he developed swelling of the left knee with restricted range of motion and limping. A complete blood count (CBC) performed on the day of presentation showed platelets of 6 x 10*3/uL with otherwise normal hemoglobin, red blood cell indices, and white blood cell count. There was no known tick exposure but Lyme serologies were obtained. The patient was sent to the emergency department.
Initial exams showed petechiae on the palate, torso, and all four extremities with swelling of the left knee (Image 1) leading to decreased range of motion and weight bearing. The family denied patient or family history of easy bleeding or bruising disorders. Laboratory evaluation was significant for platelet count of 4 x 10*3/uL, immature platelet fraction of 22.2% (Ref. range and units: 1.1% – 8.5%), prolonged activated partial thromboplastin time (aPTT) of 47s. (Ref. range and units: 24 – 36 seconds), normal prothrombin time (PT) of 14.7s. (Ref. range and units: 12.4 – 14.7 seconds), fibrinogen 460 mg/dL (Ref. range and units: 170 – 410 mg/dL). Due to prolonged aPTT, mixing studies were completed to rule out a coagulation factor deficiency or inhibitor. Quantitative Factor XII, XI, VIII, and IX levels were normal. An ultrasound showed an echogenic joint effusion distending the knee capsule (Image 2) consistent with left knee hemarthrosis. Patient was admitted for further management.
On hospital day one, peripheral blood smear showed findings consistent with ITP. X-rays showed no fracture or traumatic findings. Intravenous immunoglobulin (IVIG) and steroids were initiated due to severe thrombocytopenia with hemarthrosis. On hospital day two, the patient demonstrated improved knee swelling and range of motion along with improved platelet count to 29 x 10*3/uL. Arthrocentesis and additional imaging were deferred given clinical improvement. The Lyme Disease screening assay resulted positive (Ref. range and units: Negative, a positive screen result is considered presumptive positive for Lyme Disease with confirmatory immunoblot sent). Repeat screening assay and confirmatory immunoblot were obtained but empiric antibiotics were not started.
Two days following hospital discharge, repeat Lyme Disease screening resulted positive for IgM and IgG and a 28-day course of doxycycline was prescribed. Patient was seen by infectious diseases and hematology five days after hospital discharge. He had no ongoing bleeding symptoms and near resolution of knee swelling and pain. Initial immunoblot testing resulted in positive IgM bands 3/3 and IgG bands 9/10 (Ref. range and units: Lyme Disease IgM immunoblot requires reactivity to 2 of 3 specific borrelial proteins to be considered positive, Lyme Disease IgG immunoblot must show reactivity to at least 5 of 10 specific borrelial proteins to be considered positive). Stronger consideration was given to Lyme arthritis as contributive to clinical presentation. At final follow up, evaluation showed a robust platelet response to 738 x 10*3/uL without evidence of recurrent symptoms.