Discitis

Discitis is an inflammatory condition involving the intervertebral discs and end plates of vertebral bodies. It encompasses a spectrum of conditions that includes discitis, spondylodiscitis, and vertebral osteomyelitis.

Discitis is uncommon. However, there is a bimodal peak in children, those under 6 years and adolescents. Neonates can also be affected. Discitis most commonly occurs within the lumbar region, then thoracic and rarely cervical.

How does discitis present in children?

The presentation really depends on the age of the child.

• Neonates – septic/irritable
• 6 months – 6 years – non-specific limp, refusal to walk, back pain (often difficult to localise), low grade or no fever
• >6 years – back pain (more localised), fever, generally unwell

The underlying pathology is usually infectious. A wide range of causative pathogens have been identified. In children, discitis is more likely to be due to haematogenous spread, though pathogens can be introduced directly during surgery or trauma. Discitis has also been reported as a very rare complication of button battery ingestion.

Discitis is often a result of inflammation secondary to a low-grade bacterial infection. Some authors believe that discitis is non-infectious in origin and actually the result of minor trauma. However, this can be difficult to prove, given how often young children bump into things.

Adults and children have different vasculature, and that might explain the different pathology. Vertebral discs vascularize during early childhood, with blood vessels appearing in the vertebral end plates by seven years of age. This allows direct haematogenous spread with the deposition of bacterial emboli within the disc itself. In older children, the subchondral spongy bone is supplied by end arteries. If septic emboli lodge there, they can cause bone infarction with vertebral osteomyelitis and subsequent extension through the endplate into the disc. Younger children tend to develop discitis first, and older children vertebral osteomyelitis.

Which organisms cause discitis?

Pyogenic

• Staphylococcus aureus – most common, present in up to 80% of cases in the first few months of life
• Kingella kingae – an important cause of discitis in children aged 6 months – 4 years
• Coagulase-negative Staph, Strep pneumoniae, Gram-negative rods, E.coli, Salmonella (important cause in patients with sickle cell disease)

Subacute/non-pyogenic:

• Mycobacterium tuberculosis (Pott disease, predominantly in developing countries)
• Brucella (unpasteurised goat cheese consumption)
• Burkholderia
• Fungi (Aspergillus, Candida, Cryptococcus) – immunosuppressed

What investigations should you consider?

Blood tests

• WCC may be slightly elevated (higher in osteomyelitis cases)
• CRP may be slightly elevated
• ESR appears to be the most sensitive lab test, with levels commonly being moderately elevated

Blood cultures

• Blood cultures are rarely positive—one study found 88% were sterile—but they can be very helpful if positive.
• Needle aspiration/biopsies also have limited yield and are therefore reserved for atypical cases or when there is no response to first-line treatment. Some authors recommend the isolation of an organism before commencing antimicrobial therapy.
• Specific serology/PCR may be useful if cultures are negative

Imaging

• Plain radiographs can show abnormalities in up to 76% of patients. Findings include loss of disc space with erosion of the vertebral end plates. These features are delayed and not usually present until the disease has been present for 2-6 weeks.
• MRI is the imaging modality of choice, with a sensitivity of 96% and specificity of 92%. It can reduce diagnostic delay and can identify adjacent inflammatory lesions requiring prolonged treatment +/- surgical intervention. It is also used to monitor improvement/resolution. Radiological resolution can take time.

How do you treat discitis in children?

Treatment predominantly focuses on bed rest, analgesia, and, if possible, targeted anti-microbial therapy. If osteomyelitis is identified, it warrants antibiotic treatment (initially IV with subsequent step-down). The use of antibiotics in ‘sterile’ discitis is more controversial as there are case reports of spontaneous resolution. However, most authors recommend broad-spectrum IV antibiotics, adjusted when results are available, for several days. There is no current consensus on duration. This can subsequently be stepped down to oral if there is a good response to immobilisation.

References

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