What Imaging Evaluation Should I Consider In An 11-Year-Old Male With A 2-Week History Of Fever And Complaints Of Low Back Pain And A Progressive Limp?
This clinical scenario is concerning for an infectious process involving the vertebral bodies (osteomyelitis) and/or intervertebral disk spaces (discitis). In addition, a malig- nant process should be ruled out of the differential diagnosis. These clinical entities are uncommon in children but can be significant illnesses with substantial morbidity and mortality. It is thought that a preceding infection (whether bacteremia from organisms such as Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae or GI/GU pathogens such as Escherichia coli) may hematogenously spread to the vertebral bodies and/or disk spaces.
Although both entities may present with these clinical signs and symptoms, an 18-year review of discitis and vertebral osteomyelitis in children indicated that children with discitis were usually younger than 5 years with no or low-grade fever. Refusal to walk occurred secondary to a lesion usually in the lumbar area. However, children with osteomyelitis tended to be older and have fever and pain in cervical, thoracic, or lumbar regions. When suspicious of either of these infectious processes, it is important to define the anatomy and extent of disease for prognosis, appropriate intervention, determination of the microbiology, treatment, and management.
The initial studies one may order consist of plain x-rays of the spine. Most authorities believe changes consistent with a diagnosis of osteomyelitis (such as periosteal elevation and bony destruction) will not be present for 7 to 10 days and discitis approximately 2 to 3 weeks. Figure 46-1A and B shows bony destruction of the L4-L5 vertebral bodies of a 9-month-old child with a history of refusal to sit up and bear weight coupled with fever for 2 weeks. In the pediatric population, Fernandez et al indicate that roughly three- fourths of patients with discitis had abnormalities detected via plain films.
Other imaging modalities such as nuclear bone scan and computed tomography (CT) scan are relatively nonspecific. Figure 46-1C shows the aforementioned 9-month-old with enhancement in the lower lumbar vertebral bodies, but it is difficult to determine the extent of disease, the consistency of the abnormality present, and the anatomic land- marks. Although one of these diagnostic modalities may be abnormal, it may require that an additional study be performed to better delineate the clinical scenario.
Figure 46-1. (A) Frontal and (B) lateral radiographs of lumbar spine show narrowing of L3-L4 intervertebral disk space with irregularity of the adjacent vertebral end plate (arrow). (C) Radioisotope bone scan shows increased activity at L3 and L4 levels.
Magnetic resonance imaging (MRI) with contrast has become the imaging diagnostic of choice in order to define the anatomy and pathology of the central nervous system, vertebral bodies, and intervertebral spaces, as well as the musculoskeletal areas in which there may be local extension of disease. MRI is widely available, and an additional advantage to this procedure is the potential ability to perform image-guided sampling (needle biopsy) for both diagnostic and therapeutic purposes. Some considerations prior to MRI include sedation of young infants and/or children and whether a contraindication to the contrast exists.
Figure 46-2 shows a T2-weighted image of a child’s upper thoracic spine demonstration of osteomyelitis with destruction of a vertebral body, and discitis. In addition, arrows indicate a paraspinous phlegmon and/or hemorrhage.
Figure 46-2. T2-weighted image of the upper thoracic spine demonstrating osteomyelitis, with destruction of the vertebral body, and discitis. The white arrows define a thin band of high signal intensity in the anterior spinal tissues, representing a paraspinous phlegmon and/ or a small collection of hemorrhage. Despite this degree of apparent destruction and spinal cord edema, no neurologic symptoms or signs were noted. (Reproduced with permission from Pediatrics, Vol. 105, Page(s) 1299-1304, Copyright © 2006 by the AAP.)
Although plain films may initially be performed to evaluate for the presence of trauma or lytic lesions, MRI is often utilized for definitive diagnosis. In the pediatric review, of 13 patients with vertebral osteomyelitis, only 46% of plain films were abnormal, indicat- ing that MRI may be necessary for detection such that treatment and management may be given. In general, MRI was the recommended imaging modality of choice for pediatric infections of the spine, as 9 of 10 patients with discitis and 11 of 11 children with vertebral osteomyelitis were detected by MRI.
The most common organism detected by biopsy is S aureus, with methicillin-resistant S aureus (MRSA) comprising a significant portion of isolates. Other organisms include S pyogenes, S pneumoniae, and gram-negative organisms (E coli) associated with a prior his- tory of urinary tract infections. Bartonella henselae is an uncommon cause of vertebral osteo- myelitis, but should be considered in individuals with cat exposure. Lastly, Mycobacterium tuberculosis, or “Pott disease” (spondylitis more commonly affecting the cervical and tho- racic vertebrae), may be suspected in patients with a positive TB skin test (TST), interferon gamma release assay (IGRA), and/or associated tuberculosis (TB) risk factors.
Given the broad differential, it is crucial to obtain microbiologic identification and susceptibilities to guide antimicrobial therapy. If cultures remain negative, options for management include a repeat biopsy or empiric anti-staphylococcal therapy. If the local epi- demiology suggests the percentage of MRSA is significant, consideration of vancomycin or clindamycin is reasonable. Other anti-staphylococcal drugs targeting methicillin-susceptible S aureus include nafcillin, oxacillin, or cefazolin. Clindamycin may be a prudent choice as it provides empiric coverage of both staphylococci and streptococci, with the added benefit of bone penetration.
The proposed length of therapy is unknown, but generally a minimum of 4 to 6 weeks with clinical improvement, normalization of inflammatory markers (such as erythrocyte sedimentation rate [ESR], C reactive protein [CRP]), +/− repeat imaging used for deter- mining duration of antibiotics.
Fernandez M, Carrol C, Baker CJ. Discitis and vertebral osteomyelitis in children: an 18 year review. Pediatrics. 2000; 105(6):1299-1304.
Mahboubi S, Morris MC. Imaging of spinal infections in children. Radiol Clin North Am. 2001;39(2):215-222.