Abstract
<title>Abstract</title> <p> <bold>Background</bold> Spinal subdural abscess (SSA) is rarely reported in elderly critically ill patients, and its association with iliopsoas abscess remains poorly understood. Staphylococcus aureus infection complicated by central nervous system involvement carries a mortality rate exceeding 30%. We report a rare case of methicillin-susceptible S. aureus (MSSA) SSA secondary to an iliopsoas abscess and propose a potential route of infection. <bold>Case presentation</bold> A 75-year-old man was admitted with low back and leg pain, fever, altered mental status, and progressive lower-limb weakness. He was diagnosed with sepsis, a left iliopsoas abscess, and an SSA at the T12–S1 level. Management comprised empirical broad-spectrum antibiotics followed by targeted therapy with linezolid plus levofloxacin guided by microbiological findings, computed tomography-guided drainage of the iliopsoas abscess, emergency arachnoid-sparing surgical drainage of the spinal abscess, and organ function support. Cultures identified MSSA. The infection was controlled, organ function recovered, and neurological function improved significantly. At discharge, lower-limb muscle strength had improved to grade 4/5, with bowel and bladder function returning to normal; no recurrence was observed during follow-up. Imaging supported a potential route whereby the iliopsoas abscess eroded the epineurium at the lumbosacral foramen and spread into the subdural space. <bold>Conclusions</bold> Rapid diagnosis, pathogen-targeted antimicrobial therapy, and arachnoid-sparing surgical drainage are key to the successful treatment of this rare condition. The proposed infection pathway provides new insights into the pathogenesis of rare spinal infections. </p>