Spinal Subdural Abscess in the Emergency Department: A Rare Diagnosis in an Immunocompetent Host.

Spinal subdural abscess is an exceptionally rare and potentially life-threatening spinal infection characterized by the accumulation of purulent material between the dura and arachnoid mater. In contrast to the more common spinal epidural abscess, spinal subdural abscesses have been reported in fewer than 80 cases, often in pediatric, postoperative, or immunocompromised patients. This case represents the fourth documented instance of a spinal subdural abscess in an immunocompetent adult without identifiable risk factors or a known source of infection and the first reported in emergency medicine literature. A 60-year-old immunocompetent woman presented to the emergency department with atraumatic low back pain initially attributed to lumbar radiculopathy. She returned six days later with worsening bilateral radicular pain, urinary incontinence, and systemic symptoms. Magnetic resonance imaging (MRI) revealed a large subdural fluid collection from T2 to L5, concerning for spinal subdural abscess. Emergent surgical decompression revealed frank purulence within the subdural space. Cultures grew Streptococcus intermedius, a rare pathogen in spinal infections. The patient completed an 8-week course of intravenous cefazolin and recovered fully with resolution of neurologic deficits. Spinal subdural abscesses can progress rapidly, causing widespread neurologic impairment due to the continuity of the subdural space. This case underscores the importance of maintaining a high index of suspicion for spinal infections in patients presenting with back pain and neurological deficits, even in immunocompetent patients. Early MRI and surgical consultation are essential to prevent irreversible neurological damage and optimize patient outcomes.