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Diskitis is an inflammatory process involving the intervertebral disks and the end plates of the vertebral bodies. It is associated with characteristic clinical and radiologic findings, but information about diskitis is derived primarily from case reports and retrospective studies of small numbers of patients.
Diskitis has been reported under a variety of other names, including spondylodiskitis, pyogenic infectious spondylitis, spondylarthritis, acute osteitis of the spine, intervertebral disk space infection, and benign osteomyelitis of the spine. The definition of diskitis varies among studies, and it is often difficult to differentiate disk space inflammation alone from vertebral osteomyelitis, particularly in young children <6 years old. Disk space inflammation likely is part of a spectrum of disease that includes vertebral osteomyelitis, but diskitis appears to have a more benign clinical course. ,
There has been no consistent approach to the diagnosis, treatment, and long-term follow-up of patients with diskitis. Knowledge about the incidence, causes, and optimal treatment of this infection therefore remains limited.
Epidemiology and Etiology
Although the incidence of diskitis is unknown, it appears to be uncommon. In one center, diskitis occurred at a rate of approximately 1–2 cases per 30,000 clinic visits per year. Most cases occur among children 6 years of age or younger, , although cases have been reported for older children and adolescents. Disk space infection in adults most commonly occurs in the postoperative setting. Spontaneous diskitis is uncommon in adults, , but when reported, it has been associated with older age, diabetes mellitus, and systemic infection.
Diskitis is probably the result of low-grade bacterial infection of the disk space. , , , , Some investigators think that intervertebral disk inflammation is noninfectious and the result of antecedent trauma to the spine.
Most blood culture results obtained from patients with diskitis are negative. If positive, Staphylococcus aureus is the most common isolate ( Table 77.1 ). Other organisms isolated from blood cultures or disk aspirates from affected children have included S. epidermidis, Kingella kingae , , , anaerobes, gram-negative enteric organisms, , Streptococcus pneumoniae, and Brucella species. In most cases, cultures of intervertebral disk specimens are sterile ( Table 77.2 ).
TABLE 77.1
Results of Blood Cultures for Children With Diskitis
| Study | No. of Patients | Blood Cultures | |
|---|---|---|---|
| No. of Cultures | No. of Positive Results | ||
| Smith and Taylor (1967) | 20 | 24 | 0 |
| Wenger et al. (1978) | 41 | 22 | 10 a |
| Scoles and Quinn (1982) | 29 | 9 | 0 |
| Crawford et al. (1991) | 36 | 28 | 2 b |
| Ryoppy et al. (1993) | 18 | 0 | 0 |
| Brown et al. (2001) | 11 | 11 | 0 |
a Staphylococcus aureus (9 results); diphtheroids (1 result).
TABLE 77.2
Results of Disk Space Aspirates for Children With Diskitis
| Study | No. of Patients | No. of Biopsies or Aspirates | No. of Positive Culture Results |
|---|---|---|---|
| Smith and Taylor (1967) | 20 | 3 | 1/3 a |
| Spiegel et al. (1972) | 48 | 15 | 5/15 b |
| Wenger et al. (1978) | 41 | 9 | 6/9 c |
| Scoles and Quinn (1982) | 29 | 6 | 2/6 d |
| du Lac et al. (1990) | 12 | 8 | 6/8 e |
| Crawford et al. (1991) | 36 | 3 | 0/3 |
| Ryoppy et al. (1993) | 18 | 17 | 0/17 |
| Brown et al. (2001) | 11 | 3 | 0/3 |
| Garron et al. (2002) | 42 | 35 | 22/35 f |
a Staphylococcus aureus (1 result).
b Moraxella spp., Staphylococcus aureus, Streptococcus pneumoniae, diphtheroids, and micrococcus (1 result each).
c Staphylococcus aureus (6 results; 1 also showed α-hemolytic Streptococcus ).
d Klebsiella spp. and Staphylococcus aureus (1 result each).
e Moraxella spp. (1 result) and Staphylococcus aureus (5 results).
f Staphylococcus aureus (12 results), Kingella kingae (6 results), Staphylococcus epidermidis (1 result), Clostridium clostridiiforme (1 result), Streptococcus spp. (1 result), and Coxiella burnetii (1 result).
Viruses have not been isolated from disk space cultures. Mycobacterium species and Candida species have been isolated by disk space aspiration from older adults .
Pathogenesis and Pathologic Findings
The lumbar or lower thoracic spine is involved in most cases. There are rare reports of diskitis involving the cervical spine. , Usually only one disk space is involved, although patients with involvement of two intervertebral disk spaces have been reported.
The difference in blood supply to the vertebral bodies and disk spaces in children compared with adults may explain the age-related incidence of diskitis. In the young child, there are widespread anastomoses between intraosseous arteries supplying the vertebrae. These vessels begin to involute at about 8 months of age and are few in number by the age of 7 years. By the third decade of life, the anastomoses have atrophied fully, and peripheral periosteal arteries develop. As a result of this rich blood supply to the vertebral end plates, a septic embolus in a child leads only to small areas of vertebral end plate infarction or infection, with disproportionate involvement of the intervertebral disk. A septic embolus in an adult results in a much larger area of vertebral body infarction and subsequent infection, which causes vertebral osteomyelitis. ,
The intervertebral disk is composed of the cartilaginous plate, the annulus fibrosus, and the nucleus pulposus. Examinations of cadavers have demonstrated that blood vessels exist in the cartilaginous end plates until 7 years of age and in the annulus fibrosus until 20 years of age. This may explain the finding of disk space inflammation or infection with relative sparing of the vertebral body that is seen in children. An ovine animal model of diskitis demonstrates that infection of the disk impedes disk development but does not seem to affect vertebral body growth.
MRI findings in children with diskitis suggest a pathophysiologic sequence in which infection or inflammation begins in the metaphyseal bone near the vertebral endplates, with anterior spread to the disk region and the adjacent vertebral end plate. , Histologic examination of disk biopsy specimens from children with diskitis reveals subacute or chronic nonspecific inflammation. For some children with the characteristic clinical and radiologic findings of diskitis, histologic results are normal. ,
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