Rationale: Iliopsoas abscess, mainly caused by Staphylococcus aureus, occurs via the bloodstream or spread from adjacent infected organs. Although a few cases regarding primary iliopsoas abscess caused by Streptococcus dysgalactiae subspecies equisimilis (SDSE) with accompanying disseminated foci have been reported to date, there has been no case report on solitary primary iliopsoas abscess caused by SDSE.
Patient concerns: An 85-year-old Japanese woman presented with worsening right hip pain and fever after an exercise. Hip computed tomography revealed a right iliopsoas abscess (iliac fossa abscess), and intravenous cefazolin was started as a treatment based on the creatinine clearance level on admission.
Diagnoses: Blood cultures were positive for β-hemolytic Lancefield group G gram-positive cocci arranged in long chains, which were identified as SDSE by matrix-assisted laser desorption/ionization. No other disseminated foci were found upon performing whole computed tomography and transthoracic echocardiography. The patient was diagnosed with an SDSE solitary iliopsoas abscess.
Interventions: The antimicrobial was appropriately switched to intravenous ampicillin on day 2, with the dosage adjusted to 2 g every 6 hours based on the preadmission creatinine clearance, followed by oral amoxicillin (1500 mg, daily).
Outcomes: The abscess disappeared without drainage on day 39, and the patient remained disease-free without recurrence or sequelae during a 6-month follow-up period.
Lessons: SDSE can cause a solitary primary iliopsoas abscess, which can be successfully treated with an appropriate dose of antimicrobials without draining the abscess.
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