Severe multisite methicillin-susceptible Staphylococcus aureus infection in an elderly critically ill patient: a case report of spinal subdural abscess with concomitant iliopsoas abscess

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 SSA in an elderly critically ill patient with a coexisting methicillin-susceptible Staphylococcus aureus (MSSA)-positive iliopsoas abscess, and we discuss a presumed anatomical pathway of contiguous spread—proposed as one of several plausible hypotheses rather than an established route—based on the clinical history and radiological findings. 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 a spinal subdural abscess extending from T12 to S1. Iliopsoas abscess culture identified MSSA; intraoperative spinal specimen cultures were negative, presumably because of prior antibiotic exposure, and the spinal subdural abscess was therefore presumptively attributed to MSSA, although hematogenous seeding could not be excluded. Following CT-guided iliopsoas drainage, targeted antimicrobial therapy, and arachnoid-sparing L1–L3 decompressive laminectomy, the infection was controlled and organ and neurological function recovered. No clinical recurrence was observed during 6 months of follow-up. Rapid diagnosis, pathogen-targeted antimicrobial therapy, and arachnoid-sparing surgical drainage were key to the successful treatment of this rare condition. This case highlights a presumed route of contiguous spread from an iliopsoas abscess to the spinal subdural space; however, this should be regarded as one of several plausible hypotheses rather than an established route, as hematogenous seeding cannot be excluded, and further investigation is warranted.