Spinal epidural abscess (SEA) and spinal epidural hematoma (SEH) are neurologic emergencies with distinct etiologies and treatment. Despite similarities on magnetic resonance imaging (MRI), their differentiation is usually possible with meticulous history taking and neurologic examinations. We report an unusual case of SEA that developed from preceding SEH, posing a diagnostic challenge to physicians. A 65-year-old diabetic man suddenly experienced back pain and weakness of both legs when he lifted heavy luggage. He was afebrile, and his laboratory tests were mostly unremarkable. Spinal MRI consisting of T1-weighted, T2-weighted, and fat-suppressed T2-weighted images revealed an epidural mass over the L2-L4 spinous process. He was diagnosed with SEH based on his symptoms and MRI findings, and was treated conservatively using steroid pulse therapy. Despite initial improvement, he suddenly developed into septic shock and coma on the 10(th) hospital day, and died shortly thereafter. An autopsy revealed massive pus accumulation in the lumbar epidural space and brain, and a postmortem diagnosis of infected SEH associated with invasive pneumococcal disease was established. Serial MRI studies, including diffusion-weighted and/or gadolinium-enhanced T1-weighted images are warranted in patients with a presumed diagnosis of SEH receiving steroid therapy to detect such infectious transformation.