Recognizing and treating spinal infections
Spontaneous infections of the spine used to be quite rare. For reasons not well understood, spinal infections seem to be sharply on the rise in recent times.
Infections localized predominantly in an intervertebral disc is known as discitis. When localized in the vertebral bodies, the infection is known as osteomyelitis. Spinal infections can also occur in the epidural space. In reality, most infections affect a combination of the three areas.
Spinal infections, particularly with epidural extension, used to be thought of as a surgical emergency. Nowadays, most cases can be managed without open surgery through aggressive antibiotic therapy. Most patients with a spinal infection will require prolonged antibiotic therapy with or without external bracing.
Surgery is now reserved for special circumstances such as progressive neurological deficits, severe spinal cord compression, significant resultant spinal column deformity or instability, and refractory infections.
Infection and abscess formation may also develop in surrounding tissue such as the paraspinal muscles or the psoas muscles. Spinal osteomyelitis-discitis most commonly occurs in the region of the thoracolumbar junction, although it can occur anywhere in the spine.
The most common presenting sign of a spinal osteomyelitis-discitis is severe back pain and tenderness in the affected region. Pain can be so severe that the patient is terrified to move and just bumping their bed may elicit cries of agony.
When evaluating a patient with acute severe spinal pain (with or without rapidly progressing neurological deficits), always consider spinal infection in your differential. Spinal infection is implicated if the patient is febrile—but this is often not the case.
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What to do if you suspect spinal osteomyelitis-discitis?
Start with a thorough medical history
Ask the patient about red flag conditions such as cancer, trauma, known infection, osteoporosis, severe pain, progressive neurological deficits, and bowel or bladder incontinence, as well as dental work and overall dental health.
As well, inquire about diabetes, immunosuppression, hemodialysis, intravenous (IV) drug abuse, recent spinal surgery, alcoholism, and endocarditis. Spinal infections are more common in patients with these conditions.
Perform a physical examination
Start your examination by inspecting the patient's skin for infections that could indicate an infection source. Palpate the spine for particularly tender regions.
Listen to the heart for murmurs, which could indicate possible endocarditis. Check for other signs of endocarditis, such as splinter hemorrhages. Also check for signs of sepsis such as fever, hypotension, or an elevated heart rate.
Perform a full neurological exam
Neurological findings are not overly common with spinal infections. However, if they are seen, they should alert you to the risk of rapidly progressive loss of function due to acute spinal cord or cauda equina compression.
Evaluate the patient for evidence of the following findings:
- Progressive weakness
- Progressive sensory loss
- Bladder dysfunction
- Sacral dysfunction
- Signs of meningitis
If the patient shows signs of bladder dysfunction such as incontinence or retention, go ahead with a post-void bladder scan (if it’s available). When evaluating sacral function, include perineal sensation and anal sphincter function.
Evidence of associated meningitis includes fever, a change in mentation, and nuchal rigidity. Note that fever, toxicity, sepsis, and meningeal signs are often absent.
Perform laboratory testing
As part of your evaluation, draw blood for a complete blood count (CBC), metabolic panel, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) tests.
White blood cell count on a CBC is seldom elevated while ESR and CRP are usually significantly elevated in patients with spinal infections. A normal ESR argues against the diagnosis of spinal osteomyelitis-discitis.
Obtain magnetic resonance imaging
When the patient is in severe pain with no obvious cause or has newly unexplained neurological deficits associated with severe pain, get an urgent magnetic resonance imaging (MRI) of the affected region—particularly if the patient is febrile. If the index of suspicion is high, the MRI should be performed with and without IV contrast.
On MRI, T1-weighted images will show decreased signal in the infected bone. The vertebral endplates in the region may have a moth-eaten appearance alongside a collapsed and bulging disc space. In a severe case, there may be vertebral destruction and deformity.
On T2-weighted MRI images, look for increased signal in the affected region, including the disc space and surrounding vertebrae. Post-contrast T1 images often show enhancement in both the infected vertebrae and intervening disc space. However, patterns of enhancement may be variable.
On MRI scans of a patient with a suspected spinal infection, it is also important to look for enhancing epidural pathology associated with the infected spinal segments. This finding is often a collection of inflammatory tissue (not pus), which may result in the compression of neurological tissues.
When examining MRI from a patient with a suspected spinal infection, also look for evidence of large enhancing collections in the epidural space without bone or disc involvement. This may represent an infection that predominantly affects the epidural space.
In these cases, huge collections of pus may be found that extend throughout the entire spine. Perform adjacent level MRI until you find the top and bottom of the pus collection. Epidural space infections can result in rapid neurological decline and severe permanent disability, so they warrant emergent neurosurgical consultation.
Consider the need for other diagnostic imaging
If you see bone destruction or deformity on the MRI scans of a patient with a suspected spinal infection, obtain a non-contrast computed tomography (CT) scan of the region. Non-contrast CT is better at defining the degree of bone compromise.
Pay attention to the tissues surrounding the suspected area in the spine. Often, abscesses may form in surrounding musculature and other structures.
Consider a gallium scan if the diagnosis is still in question after MRI and CT imaging. Sometimes, a gallium scan will provide strong evidence of an infection. However, you may simply want to go with a percutaneous biopsy, which is a relatively innocuous procedure.
Obtain serial blood cultures and biopsies
If you’re concerned about osteomyelitis-discitis on imaging, obtain serial blood cultures. Frequently, the patient will be bacteremic and the offending organisms can be identified by blood cultures. Often, blood cultures will be negative so be prepared to order a percutaneous biopsy of the affected area.
Send biopsy specimens for formal pathological evaluation. Metastatic tumors can look very similar to infection on imaging. With biopsy specimens, obtain a full battery of bacterial cultures. Include tuberculosis, fungal testing, and cultures of the patient’s biopsy material.
How do you treat a spinal infection?
If the patient has severe or progressive neurological compromise, consult neurosurgery immediately. Otherwise, proceed with antibiotic therapy.
Start antibiotic therapy
Hold off on giving the patient antibiotics until after blood cultures and percutaneous biopsies have been obtained. Depending on the clinical setting, start presumptive antibiotic therapy after the biopsies or wait for culture results.
By far, the most common causative organism encountered in spinal infections is Staphylococcus aureus. Other organisms include Escherichia coli, Pseudomonas, Streptococcus pneumonia, Nocardia, anaerobes, and gram-negative bacteria.
A proactive treatment often involves vancomycin (for methicillin-resistant S. aureus), metronidazole (for anaerobes), ceftriaxone, or cefepime. Rifampin can also be added to the treatment.
Consult an infectious disease specialist to adjust antibiotic therapy based on the culture and sensitivity results. If the patient has a known and ongoing bacterial infection or positive blood cultures, antibiotic treatment can be initiated without a biopsy. Some authors argue that a percutaneous biopsy of the affected area should still be performed since a small percentage of cases will turn up a different organism.
However, biopsies are often negative. If this is the case, it is reasonable to repeat the biopsy to obtain a greater yield. Repeat blood cultures once or twice while you are waiting for the biopsy results.
Continue IV antibiotic treatment for 6–8 weeks or longer if symptoms persist or if there is a failure of ESR normalization. Follow IV antibiotics with oral antibiotic therapy for 6–8 weeks.
Order echocardiography imaging
As you are managing the infection with antibiotic treatments, try to determine its source. If there is no obvious primary source of the infection, order echocardiography imaging to rule out cardiac valve vegetation. Other forms of imaging such as nuclear studies may be employed to look for possible sources of infection.
Check erythrocyte sedimentation rate
During antibiotic therapy, check the patient’s ESR every 1–2 weeks. The patient’s ESR may increase before it decreases.
Mobilize the patient
Unless the spine is unstable, mobilize the patient as early as possible. With severe pain or evidence of bone destruction, place the patient in a restrictive brace when up and about. Continue use of the brace throughout the antibiotic regimens.
Obtain follow up x-rays and MRI
Get upright x-rays of the affected area at discharge and every month during treatment to rule out progressive deformity. If you suspect that the patient will fail to respond to antibiotic therapy, consider a follow-up MRI. But, keep in mind that MRI will look progressively worse for the first several weeks of treatment, and may take months to fully improve.
What is the prognosis of patients with spinal infections?
Patients generally start to feel considerably better within 1–2 weeks of antibiotic therapy. Spinal infections will eventually resolve with continual and aggressive antibiotic therapy.
If caught before severe neurological deficit or severe spinal deformity, patients may return to normal functioning. However, severe cases can be quite complex, challenging, and may require aggressive surgical management.
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- Gandhi, SV and Schulder, M. 2020. Spinal infections. American Association of Neurological Surgeons. https://www.aans.org/
- Louis, ED, Mayer, SA, and Rowland, LP. 2015. Merritt’s Neurology. 13th edition. Philadelphia: Wolters Kluwer.
- Vinas, FC, Rhodes, JR, and Stumpf, AL. 2020. Spinal infections. Medscape. https://emedicine.medscape.com/