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Archived Issues of Radiology Rounds
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Vertebral Osteomyelitis
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- Vertebral osteomyelitis should be considered in patients with unremitting focal back pain,
especially if accompanied by fever
- Plain film radiography is recommended for initial diagnostic imaging
- MRI is indicated if x-rays are normal and clinical suspicion is high; if MRI is contraindicated,
CT is recommended
- Combined gallium and bone scan is recommended when MRI and/or CT are equivocal
- CT-guided biopsy is recommended to confirm the diagnosis and identify the infectious agent
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In
the vast majority of patients, back pain uncomplicated by neurological
symptoms will resolve within 4-6 weeks without any lasting
consequences. Unfortunately, for the few patients whose back pain is
due to a more serious condition, such as vertebral osteomyelitis,
diagnosis is often delayed. Vertebral osteomyelitis accounts for 2-4%
of all cases of bone infection and is most often found in men over 50
years. Although rare, incidence is thought to be rising due to an aging
population, a higher number of immunocompromised patients, and the
increased use of intravascular devices and injected drugs.
Vertebral osteomyelitis should be considered in all patients
experiencing unremitting and/or focal vertebral pain that is not
relieved by lying down, particularly if accompanied by fever or
paravertebral symptoms indicating a psoas or other paraspinal
extension. Patients with vertebral osteomyelitis typically experience
mild pain to start with, which progressively worsens over a period of
weeks or even months. The key clinical finding is localized tenderness
of the infected bone, with palpation being more sensitive than
percussion. Infection in the cervical region is more likely to be
associated with neurological deficits. In most cases, the infection is
blood-born. Spread from Batson’s venous plexus (draining the
genitourinary tract) has been postulated. Infection may also spread
from a contiguous infection or, occasionally, be a result of direct
inoculation.
Blood cultures as well as tests for leukocytosis and elevated
erythrocyte sedimentation rate are recommended. However, none of these
tests are sensitive and, if negative, do not rule out osteomylelitis.
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Figure 1. Plain
film radiograph of spinal discitis / osteomyelitis. Lateral view
of the lumbar spine demonstrates L 3-4 disc space narrowing (arrow) and
end-plate irregularity.
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Plain Film Radiography
Radiography
should be ordered for all patients with suspected vertebral
osteomyelitis to evaluate the spine for this and other conditions.
Generally, the earliest radiographic signs of vertebral osteomyelitis
are loss of definition of a vertebral end-plate and narrowing of the
associated disc space. Although these signs do not appear until 10-21
days after the onset of infection, most patient are not seen early in
the course of infection because back pain from vertebral osteomyelitis
is generally mild at first and the symptoms disregarded. The signs may
be less conspicuous in the thoracic spine and if pre-existing
degenerative conditions of the spine are present. If radiography is not
diagnostic and the patient is febrile or has pain that is unremitting
and not explained by the plain film findings, further imaging should be
considered.
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| Comparison of Imaging Modalities for the Diagnosis of Vertebral Osteomyelitis |
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Modality
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Strengths
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Weaknesses
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| Plain film x-ray |
| Sensitive when infection well established |
| Readily accessible |
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Signs do not develop until 10-21 days after start of infection |
| MRI |
| Most sensitive for early detection (edema) |
| No radiation exposure |
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| Moderate specificity |
| Contraindications to MR, e.g. claustrophobia, pacer, etc. |
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| CT |
More sensitive than plain film for detecting bone and disc erosions |
| Less sensitive than MR to soft tissue lesions and abscesses |
| Iodinated contrast administered |
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| Gallium-Bone Scan |
May be useful if CT and/or MRI equivocal |
| Low spatial resolution |
| Requires 2 days |
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Figure 2. MRI of lumbar spine discitis/osteomyelitis. A.
Sagittal T1-weighted images of the lumbar spine in the same patient as
figure 1 demonstrate T1-hypointense signal (solid arrows) centered
around the L3-4 interspace. B. Post gadolinium sagittal
fat-suppressed T1-weighted images shows marrow (dashed arrows) and disc
enhancement with endplate erosions.
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MRI
MRI
is the most sensitive imaging modality and can shows signs of bone
marrow edema and intervertebral disc signal changes on non-contrast
images early in the course of infection. Contrast MRI scans may show
diffuse enhancement in infected bone and discs and help to demonstrate
the presence of paraspinal soft tissue and epidural extent of disease.
However, MRI is not completely specific and the diagnosis can be
confused with, for example, tumor, spondylosis, compression fracture,
or post-radiation changes. In one study, the primary diagnosis of
discitis or vertebral osteomyelitis was made in 67% of the cases where
it was initially suspected and was an alternate diagnosis in 26%. MRI
is also less specific if performed <2 weeks after the onset of
infection.
CT
If
MRI is contraindicated, CT is useful as a sensitive modality for
detecting erosions of bone and disc, and is more sensitive than
radiography in this respect. In addition, it can be helpful for
characterizing compression fractures, which may be confused with
osteomyelitis. Contrast should be used if possible. However, CT
is much less sensitive than MRI for the detection of epidural abscesses
or soft tissue lesions.
Nuclear Scintigraphy
Scintigraphy
may be useful in equivocal cases or when different sites of infection
must be identified in multifocal disease. A combination of 67Ga citrate and 99mTc-MDP bone scanning is very sensitive and more specific than gallium alone. |
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Figure 3. Percutaneous CT –guided biopsy of discitis / osteomyelitis.
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CT-Guided Biopsy
If there are radiological indications of discitis/osteomyelitis and
blood cultures are negative, CT-guided biopsy may be indicated to
confirm the diagnosis and determine the cause of the infection. If the
diagnosis was made with plain film radiography, CT is recommended for
planning a biopsy. Core biopsy samples can be taken from an abnormal
disc, soft tissue around the bone, and the vertebra itself when
technically possible. If there is an abscess, it can be aspirated.
Biopsy procedures are generally performed under local anesthesia with
conscious sedation. Patients must have normal coagulation studies and
be taken off anti-coagulant medication.
Follow-up Imaging
Follow-up imaging is not indicated in most patients because MRI
findings of discitis/osteomyelitis may persist and can even appear
worse despite a clinical response to therapy. However, follow-up MRI
may be considered if epidural or paraspinal infection is present, if
surgery is being considered for any reason, if the microbiological
agent has not been identified (particularly if there has not been a
clinical response to empiric therapy), and in any patient with no
clinical response or clinical worsening.
Routine scans at the end of treatment are not indicated, because
imaging abnormalities are expected to persist when the recommended
duration of therapy is completed. Additional imaging at this time may
be indicated if there is a concern that the extent of paraspinal
disease or its response to therapy may warrant further treatment
(medical or surgical).
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Scheduling
Radiographic imaging for suspected osteomyelitis can be performed at
all MGH facilities. MRI can be performed at Mass General Imaging in
Waltham, Chelsea, or Charlestown, or the main MGH campus. CT can be
performed at all these facilities except Mass General Imaging in
Charlestown. Nuclear medicine studies can be performed at Mass General
West Imaging in Waltham or the main MGH campus. All studies can be
ordered online via the Radiology Order Entry (http://mghroe
) or
by calling 4-XRAY (617-724-9729). CT-guided biopsies are performed only
on the main campus and can be scheduled by calling 4-PAIN
(617-724-7246).
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Further Information
For
further questions on imaging studies for osteomyelitis, please contact
Tara M. Lawrimore, M.D.
, Musculoskeletal Radiology (617-727-7717), or
James A. Scott, M.D.
, Nuclear Medicine (617-726-8758).
We
would like to thank Drs. Lawrimore and Scott as well as Nesli Basgoz,
M.D., of the Infectious Disease Unit for their advice and assistance in
the preparation of this article.
This article provided useful information about the appropriate use of imaging studies:
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References
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Baleriaux, DL and Neugroschl, C. (2004) Spinal and spinal cord infection. Eur Radiol 14: E72-83
Carragee, EJ. (1997) The clinical use of magnetic resonance imaging in pyogenic vertebral osteomyelitis. Spine 22: 780-5
Lew, DP and Waldvogel, FA. (2004) Osteomyelitis. Lancet 364: 369-79Tyrrell, PN, Cassar-Pullicino, VN and McCall, IW. (1999) Spinal infection. Eur Radiol 9: 1066-77
Winters, ME, Kluetz, P and Zilberstein, J. (2006) Back pain emergencies. Med Clin North Am 90: 505-23
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