Atraumatic hamstring tendon rupture causes massive lower extremity pyomyositis; initially read as neoplasm

INTRODUCTION: Pyomyositis is a rare bacterial infection of skeletal muscle resulting in pain, tenderness, fever, and abscess formation, most commonly caused by staphylococcus aureus. Risks factors of pyomyositis include muscle trauma, skin infection, injections, and diabetes. Pyomyositis arises from hematogenous seeding predominately affecting immunocompromised patients in moderate climates. CASE DESCRIPTION: A 53 year old female with a past medical history of HTN, HLD, OSA, and obesity initially presented to her PCP with atraumatic right sided lower back pain. The PCP referred the patient for x-ray imaging at L5-S1 that came back negative for fracture. Two weeks after the patient’s initial visit, she was seen outpatient by a radiologist that performed a targeted ultrasound of the right posterior thigh revealing a large fluid collection caused by a hamstring tear. The patient was sent by her sports medicine physician for MRI without contrast that indicated a large multiloculated cystic mass of neoplastic origin with bone marrow edema involving the right posterior ischium. The patient was referred to oncology. One month after the initial visit with her PCP, the patient presented to the ED for an evaluation of acute dyspnea and tachycardia. The patient reported fevers, vomiting, and decreased appetite occurring over the last 3 weeks. Physical examination showed tenderness with a palpable area of firmness in the posterior aspect of the proximal hamstring, that was approximately 8x10 cm with blanchable erythema. A radiologist at the hospital reviewed the outpatient MRI without contrast and was unable to distinguish whether there was a mass, hematoma, or abscess. He requested MRI with contrast and discovered a large, complex, interconnected, intramuscular abscess which involved multiple muscles in the right lower extremity, measured at 14.1 x 13.0 x 30.8 cm containing 2000 mL of fluid. Muscles involved included the entire posterior and adductor compartments of the proximal right lower extremity and multiple external rotators of the hip. MRI also found osteomyelitis of the right acetabulum and ischium. Blood cultures were obtained while in the ER and the patient was placed on IV vancomycin and cefepime. IR drainage was performed on the posterior thigh (415 cc purulence) and the gluteal abscess (80cc). Cultures showed staph aureus and the ID team switched to IV Ancef ordered for 6 weeks. Follow up MRI imaging showed continued residual pockets of abscess in the deep compartment of the thigh. Incision and drainage was performed by orthopedics and a PICC line was placed allow for discharge to a skilled nursing facility to monitor her wound healing. DISCUSSION: This case illustrates the necessity of proper imaging needed for a pyomyositis case. Although pyomyositis rarely occurs outside of both tropical environments and immunocompromised patient populations, early use of MRI with contrast is highly sensitive imaging used in diagnosing pyomyositis. Proper recognition of febrile symptoms and palpation of the effected extremity combined with correct use of imaging in this patient could have led to a correct diagnosis and allowed early treatment, preventing a lengthy hospital stay