Idiopathic septic arthritis of a lumbar facet joint associated with paraspinal abscess.

A 48-year-old woman presented with a 1-month history of severe lower back pain on a background of 24 h of mild fever and general tiredness with an associated right-sided foot drop. Five weeks after the onset and with no improvement in symptoms in spite of analgesia and physiotherapy, the patient had a lumbar spine MRI which demonstrated a collection extending from the facet joints of L5 and L6 to the iliacus muscle on the right. A CT-guided aspiration was performed with a lengthy hospital stay for intravenous antibiotic treatment.