Characteristics

• Pure discitis (infection limited to the intervertebral disc) is rare. More commonly, the infection is within the adjacent veterbrae (osteomyelitis) and spreads into the disc rather than vice versa; however, the end-plates of the adjacent vertebrae are rapidly attacked in cases of primary discitis.

• Most cases of discitis are iatrogenic, following disc injection (discography or chemonucleolysis) or surgical excision (discectomy). Discitis is rarely secondary to haematogenous spread.

• With osteomyelitis, the source of infection is either from spinal procedures (including spinal or epidural injection) or systemic infection, most commonly pelvic infection.

• The commonest organism is Staphylococcus aureus (50%–60%), although Gram-negative organisms, particularly E coli, Proteus and Pseudomonas, are increasingly pathogenic.

• In immunocompromised patients expect opportunistic pathogens. Tuberculosis must be considered in spinal infection, particularly with no history of recent spinal procedure, and in immunocompromised hosts.

Clinical features

• History of an antecedent invasive procedure or, with secondary discitis/osteomyelitis, a recent systemic infection.

• Pain localised to the particular spinal segment, but do not forget that spinal infection can track down muscle planes to present as groin or buttock abscesses. Spinal muscle spasm may also be present.

• Examination may reveal mild temperature or tachycardia. The relevant spinal segment is usually tender to palpation.

• CRP, ESR and white-cell count should be raised.

Radiological features

• Location: L3/4 and L4/5; unusual above T9 and usually involvement is limited to one disc space.

• Radiographs – plain films are usually positive 2–4 weeks after onset of symptoms – decrease in disc height, indistinct end plates with destructive end plate sclerosis.

• CT – paravertebral inflammatory mass and extension into the epidural space.

• Nuclear medicine – positive before radiographic change, with increased uptake in the disc and adjacent vertebrae; however suffers from poor sensitivity (40%).

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