Popliteal Puzzle Solved: A Rare Case of Intramuscular Cysticercosis of the Peroneus Longus Muscle.

Cysticercosis, caused by the larval form of Taenia solium, is endemic to many developing regions, with neurocysticercosis being the most recognized manifestation; however, musculoskeletal and isolated intra-muscular involvement is rare and diagnostically challenging. We report the case of a 37-year-old woman presenting with a two-week history of insidious popliteal pain in the left knee, initially evaluated by orthopedics and neurology with normal radiographs and nerve conduction studies. After referral to internal medicine, routine laboratory investigations and autoimmune markers were unremarkable, but MRI of the knee identified a well-defined cystic lesion with a central scolex, confirming intra-articular cysticercosis. The patient responded completely to oral albendazole and corticosteroids, with full symptomatic resolution and radiological normalization. This case highlights the importance of considering cysticercosis in the differential diagnosis of unexplained knee or soft-tissue pain, particularly in endemic areas; timely MRI evaluation facilitates accurate diagnosis, and conservative antiparasitic therapy can obviate the need for invasive interventions.