Abstract
BACKGROUND: Septic facet cysts are a rare phenomenon reported in the literature among immunocompromised hosts and may require operative intervention for appropriate source and symptomatic control. OBSERVATIONS: A 70-year-old male with a past medical history of immunoglobulin A lambda smoldering myeloma degenerative lumbar disease who presented with low back and radicular lower extremity pain was found to have a left L4-5 septic facet cyst with extension to the epidural space. Intraoperative cultures were positive for Nocardia species. Staging workup revealed progression to high-risk-profile multiple myeloma. LESSONS: Patients with septic facet cysts may require operative intervention for appropriate source control. Nocardia spine infections and septic facet cysts are rare and require investigation of preexisting risk factors and any potential underlying immunocompromise. https://thejns.org/doi/10.3171/CASE25220.