Abdominal Pain: An Unlikely Diagnosis

Pyomyositis is a rare infection of the striated muscle. Generally results from hematogenous spread of septic emboli. It is caused mainly by Staphylococcus aureus. The clinical presentation is unspecific and the diagnosis is often difficult and delayed.

We present the case of a previously healthy 14 years old boy, who was admitted at Emergency Department for localized pain in the left inguinal region for 2 days. No fever, urinary complaints and no history of trauma. He presented with left lower limb flexed and pain on the left iliac fossa and anterosuperior iliac spine. X-ray and ultrasound of the pelvis did not revealed any abnormal find. Analytically he had leukocytosis, with predominance of neutrophils, C-reactive protein 79.6mg/L and sedimentation velocity of 81mm in the first hour. He performed an abomino-pelvic computed tomography scan that was normal, however, he was admitted in our hospital for surveillance. In day 1 he developed fever and inflammatory signs in the left inguinal region, therefore empirical antibiotic therapy was started with intravenous Flucloxacillin and Clindamycin. Subsequently, he performed an magnetic resonance imaging that identified multiple abscesses adjacent to the left anterior-superior iliac spine and left oblique and iliac muscles. Drainage of the abscesses was performed but no etiological agent was identified. This patient completed 14 days of intravenous antibiotic therapy and was than discharged with indication to complete five weeks of antibiotic therapy. Of the cultural exams requested the patient presented three negative blood cultures and immunological study revealed to be normal.

Early diagnosis of pyomyositis is crucial and requires a high level of suspicion. In this patient it was not possible to isolate the etiologic agent probably because the abscess drainage was already performed under antibiotic therapy. Its evolution was favorable, with no associated complications and no functional limitations at the time of discharge.