Chapter 49. Diskitis

Diskitis is an uncommon inflammatory condition affecting the intervertebral disc and adjacent vertebral end plates. The available evidence implicates a low-grade bacterial infection rather than a noninfectious inflammatory process, as was previously thought. Most cases are diagnosed in children younger than 4 years, in the age range between 7 months and 16 years,1–8 and males are more frequently affected (male to female ratio is 1.7:1).6–8 Diskitis involves the lumbar spine most commonly, although any area of the spine may be involved. As the findings on history and physical examination are often nonspecific, a high index of suspicion is required to make the diagnosis.

While several theories have been proposed including infection, noninfectious inflammation,9,10 and trauma,11 the weight of evidence implicates a bacterial infection involving the disc and vertebral end plate.1,6,9,12–14 This theory is supported by cultures of intervertebral material and blood.1,6,8–10,14 Diskitis likely represents one end of the spectrum of infection involving the anterior elements of the spine, the manifestations of which depend upon differences between the microcirculation in infants and children versus adults. Vascular channels between the vertebral body and the disc are present in infants and children, providing a portal for hematogeneous seeding of the disc. These channels are not present in adolescence and adulthood, which explains the preponderance of vertebral osteomyelitis rather than diskitis in these older age groups. While diskitis may resolve spontaneously in a subset of patients treated only by symptomatic measures, the disease process may progress and require operative debridement.12,15,16 Ring et al. found recurrent symptoms and/or a prolonged course in 18% of patients with diskitis treated with intravenous antibiotics versus 67% who received no antibiotics.12

The clinical findings associated with diskitis differ infants and toddlers, compared with older children (Table 49–1). The presentation in infants/toddlers is usually nonspecific, often resulting in a delay in diagnosis. Occasionally, parents may report a recent infectious illness (e.g., upper respiratory tract infection) or a mild trauma. Symptoms in the infant and toddler include general irritability, crying at night, and the refusal to walk. When severe, symptoms may result in the refusal to stand or sit with a preference for bed rest.1,3,6,13 Older children with diskitis often experience well-localized back pain, which may radiate to the hip region or legs. Gait disturbance is a common finding in this age group,5,7,9 and pain may be referred to the abdominal region.

Low-grade fevers may be present, but patients usually do not appear acutely ill. Physical examination can demonstrate local tenderness with palpation, paravertebral muscle spasm, hamstring contracture, and occasionally a positive straight-leg raise test. When the child is asked to pick up an object off the floor, he or she may squat down rather than bending forward, avoiding painful spinal flexion (coin test).3 Mirovsky et al.17 reported a positive Gower's sign in four patients with diskitis.

The differential diagnosis includes infectious, inflammatory, neoplastic, and developmental conditions (Table 49–2). Other bacterial pathogens include brucella and salmonella, often in the context of underlying sickle cell disease); granulomatous infections such as tuberculosis may present in a similar fashion. Fungal infections such as Cryptococcus neoformans are rare but should be considered, especially in the immunocompromised host. Neoplastic diseases such as eosinophilic granuloma, leukemia, and lymphoma must be considered. Inflammatory conditions such as juvenile idiopathic arthritis may present with symptoms similar to diskitis. Scheuermann disease, also known as juvenile kyphosis) is a deformity in the thoracic or thoracolumbar spine. Scheuermann disease can cause back pain in adolescents, and the presence of vertebral wedging (of five or more degrees with involvement of three or more consecutive vertebrae) and Schmorl's nodes (herniations of the nucleus pulposus) will establish the diagnosis though Schmorl's nodes may also be seen in Wilson disease, sickle cell disease, and spinal stenosis. In addition, symptoms may be referred from other locations such as the abdomen or the hip/pelvis. Septic arthritis of the sacroiliac joint may mimic diskitis, as may intra-abdominal causes such as appendicitis and pyelonephritis.

Laboratory Studies

Laboratory examination should include complete blood cell count, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level and blood cultures. While the WBC may be normal, the ESR is elevated in nearly all patients with diskitis. The CRP can be elevated in the early phase of infection and it is valuable to follow in observing the response to therapy. While blood cultures are negative in the majority of patients, a positive culture is more likely, when symptoms have been present for less than 6 weeks.6 Wenger et al.15 reported positive results in only 41% of blood cultures. Similarly, positive cultures are infrequent following open biopsy or aspiration of the disc space. Garron et al.14 reported positive cultures in 61% following aspiration of the disc space. Factors which may decrease the likelihood of obtaining a positive culture include insufficient sampling, previous antibiotic treatment or inadequate specimen collection and culture techniques.3,12,18,19 The most common organism isolated is Staphylococcus aureus.1,6,9,12,14,20 The second most common pathogen is Kingella Kingae,1,14,21 which has recently been recognized as a common organism in osteoarticular infections in young children.22

Radiologic Imaging

Plain radiographs are normal during the early phase of the disease, and intervertebral disc space narrowing occurs 2–4 weeks after the onset of symptoms (Figure 49–1). Additional findings may include a loss of lumbar lordosis, bony demineralization with localized erosion at the vertebral margins, and loss of vertebral height. In the recovery phase, usually after 2–3 months, sclerosis from remineralization may be observed at the margins of the adjacent vertebral bodies (Figure 49–1). While vertebral height may be restored during growth, disk space narrowing typically persists, and in some cases the adjacent vertebrae may become fused1,9,23 or enlarged (vertebra magna).1,10,23 Involvement of more than one disc space is rare, and the posterior elements are spared.1 Abscess formation may be observed, but rarely requires additional measures for treatment.

A technetium bone scan may demonstrate a focal increase in uptake prior to the appearance of abnormalities on plain radiographs, and the diagnostic accuracy ranges from 72% to 100%.3,5,6,8,9,24 Magnetic resonance imaging provides the most detailed information, including the extent of the inflammatory process, the condition of disc space and surrounding soft tissue (Figure 49–2),25 and may potentially reduce the time to diagnosis.3 While computed tomography provides the best bony detail, and may also identify endplate irregularities/erosions and abscesses, this modality is typically utilized to guide a disc space aspiration or biopsy in selected cases. Diagnostic tests are summarized in Table 49–3.

Once a diagnosis is established, the treatment is aimed at both alleviating discomfort and eradicating the disease. Symptomatic treatment measures include activity restriction (bed rest is the traditional standard) and bracing (more common today). A thoraco-lumbo-sacral orthosis is worn when the patient is upright for a period of at least 4–6 weeks. While many cases of diskitis resolve spontaneously (symptomatic treatment only), most authors recommend empiric antibiotic treatment based upon evidence implicating a bacterial cause for diskitis.1,5,7,8 Empiric intravenous antibiotics (effective against staphylococci) are typically started once blood cultures have been obtained, and patients are usually converted to an oral agent depending on both the clinical response and a sequential assessment of inflammatory markers (CRP, ESR). The specific antibiotic is modified based upon culture results; the duration of therapy is typically 4–6 weeks. A computed tomography guided needle aspiration of the disc space (or open biopsy) is indicated when there has been a failure to respond to empiric antibiotic therapy. Recommended antibiotics are listed in Table 49–4.12 Spontaneous interbody fusion may occur even in treated patients, but does not appear to affect the outcome.1,9,19,23 Surgery is rarely indicated in the treatment of diskitis. An open biopsy should be considered in patients who have not responded to empiric therapy, or when another diagnosis is suspected. Decompression and/or debridement may be indicated in the extremely rare case in which there are neurologic findings on presentation, or neurologic symptoms develop during the course of treatment. An algorithm showing the management of diskitis is summarized in Figure 49–3.