An Interesting Presentation of Lyme Pseudothrombophlebitis

An 8-year-old boy presented to the emergency department with swelling and pain of his left knee and calf for approximately 1 week. His examination was significant for moderate knee effusion and swelling of the posterior calf with erythema and warmth of the affected areas. An ultrasound obtained at an outside hospital showed a large heterogeneous mass in the gastrocnemius, and a magnetic resonance imaging revealed a large, heterogeneous, rim-enhancing collection in the medial head of the left gastrocnemius muscle with surrounding myositis involving the gastrocnemius muscle. The child was taken to the operating room by the orthopedic team for drainage and irrigation of the knee effusion and of the collection in the gastrocnemius. The diagnosis of Lyme pseudothrombophlebitis was made through Lyme serology testing of aspirated fluid. He improved after this drainage but required a prolonged antibiotic course.