Spinal infections can be identified by the anatomical location involved: the vertebral column, the spinal canal, intervertebral disc space, and adjacent soft tissues. Infections may originate from bacteria or fungal organisms and may occur following a surgery. Most postoperative infections occur between three days and three months post-surgery.
Vertebral osteomyelitis is the most widespread variety of vertebral infection. It can progress from direct open spinal trauma, infections in surrounding areas, and bacteria that spreads to a vertebra from the blood.
Intervertebral disc space infections involve the area between adjacent vertebrae. Disc space infections can be divided into three subcategories: adult hematogenous (spontaneous), childhood (discitis), and postoperative.
Spinal canal infections include spinal epidural abscess, an infection that develops in the space around the dura (the tissue which surrounds the nerve root and spinal cord). Subdural abscess is much more rare, affecting the potential space between the dura and arachnoid (the thin membrane of the spinal cord, placed between the dura mater and pia mater). Infections within the spinal cord parenchyma (primary tissue) are known as intramedullary abscesses.
Adjacent soft-tissue infections include thoracic and cervical paraspinal lesions, along with lumbar psoas muscle abscesses. Soft-tissue infections most commonly affect younger patients and are not seen often in older people.
INCIDENCE AND PREVALENCE
Vertebral osteomyelitis affects about 26,170-65,400 people annually.
- Epidural abscess is relatively rare, with 0.2-2 cases for every 10,000 hospital admissions. However, 5-18% of patients who have vertebral osteomyelitis or disc space infection caused by contiguous spread eventually develop an epidural abscess.
- Certain studies suggest that the incidence of spinal infections is now increasing. This sudden increase may be related to increased utilization of vascular devices and other forms of instrumentation and to a growth in intravenous drug abuse.
- About 30-70% of patients who have vertebral osteomyelitis have no obvious prior infection.
- Epidural abscess may occur at any age, but they are most prevalent in people aged 50 and older.
- Although treatment has improved greatly recently, the death rate produced from spinal infection still sits at an estimated 20%.
Risk factors for developing spinal infection include conditions that compromise the immune system:
- Advanced age
- Long-term systemic usage of steroids
- Intravenous drug use
- Human immunodeficiency virus (HIV) infection
- Diabetes mellitus
- Organ transplantation
Surgical risk factors include surgeries of high blood loss, long duration, implantation of instrumentation and multiple, or revision, surgeries at the same site. Infections occur in 1-4% of surgical cases, in spite of the numerous preventative measures doctors follow.
Spinal infections may be caused by a bacterial or a fungal infection that originated from part of the body, which has since been carried into the spine through the bloodstream. The most common source of spinal infections is a bacterium known as staphylococcus aureus, the next most common being Escherichia coli.
Spinal infections can occur after a urological procedure, as the veins located in the lower spine come up through the pelvis. The most common area of the spine affected is the lumbar region. Intravenous drug abusers are more vulnerable to infections in the cervical region. Recent dental procedures increase the risk of spinal infections, as bacteria that can be introduced into the bloodstream during the procedure may travel to the spine.
Intervertebral disc space infections most likely begin in one of the contiguous end plates, and the disc is infected secondarily. In children, some controversy as to the origin exists. Most cultures and biopsies in children produce negative results, prompting experts to believe that childhood discitis may not be an infectious condition, but instead caused by partial dislocation of the epiphysis (the growth area near the end of a bone), resulting from a flexion injury.
Symptoms vary as per the type of spinal infection. However, pain is generally localized initially at the site of the infection. In postoperative patients, these additional symptoms present:
- Wound drainage
- Redness, swelling, or tenderness near the incision
- Severe back pain
- Muscle spasms
- Neurological deficits: weakness and/or numbness of arms or legs, incontinence of bowels and/or bladder
- Weight loss
- Difficult or painful urination
INTERVERTEBRAL DISC SPACE INFECTIONS
Patients may have few symptoms at first, but eventually develop extreme back pain. Generally, younger, preverbal children do not possess a fever nor appear to be in pain, but they will refuse to flex their spines. Children age 3-9 usually present with back pain as the predominant symptom.
Postoperative disc space infection may occur after surgery. It occurs, on average, one month post-surgery. The pain is typically alleviated by bed rest and immobilization, but increases with movement. If left untreated, the pain grows progressively worse and unmanageable, unresponsive to even prescription painkillers.
SPINAL CANAL INFECTIONS
Adult patients typically progress through the following clinical stages:
- Severe back pain with fever and local tenderness located in the spinal column
- Nerve root pain that radiates from the infected area
- Weakness of voluntary muscles and bowel/bladder dysfunction
In children, the most overt symptoms are hip tenderness, prolonged crying, and obvious pain when the area is palpated.
ADJACENT SOFT-TISSUE INFECTIONS
Generally, symptoms are nonspecific. If a paraspinal abscess occurs, the patient may experience flank pain, a limp, or abdominal pain. If a psoas muscle abscess occurs, the patient may feel pain radiating to the hip or thigh area.
WHEN AND HOW TO SEEK MEDICAL CARE
Seek medical care if symptoms of a spinal infection occur. Early diagnosis and treatment can preclude the progression of an infection, limiting the degree of intervention needed to treat the infection. Delaying care may cause the infection to progress, inspiring irreversible damage to boney and soft tissue structures of and around the spine.
Signs of spinal infection emergency (Seek care immediately):
- Development of new neurological deficits (e.g. weakness of arms or legs and/or bowel/bladder incontinence)
- Fever not controlled with medication.
The largest challenge is making an early diagnosis before serious morbidity occurs. Diagnosis typically requires an average of one month, but it can require as long as six months, impeding effective and timely treatment. Most patients do not seek medical attention until their symptoms become severe or debilitating.
Specific laboratory tests may be helpful in helping to diagnose a spinal infection. It may be useful to receive blood tests for acute-phase proteins, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels. Both ESR and CRP tests are typically good indicators as to whether any inflammation is occuring in the body (the higher the level, the more likely it is that inflammation is present). Inflammation serves as the body’s natural response to infection, so these markers can be monitored to assess the presence of infection, along with the effectiveness of treatment. These tests alone, however, are limited, and other diagnostic tools are usually needed.
Identification of the organism is required, and this can be accomplished through computed tomography-guided biopsy sampling of the disc space or vertebrae. Blood cultures, preferably taken during a fever spike, may also assist in identifying the pathogen involved in the spinal infection. Proper identification of the pathogen is required to narrow the antibiotic treatment regimen.
Imaging studies are required to pinpoint the location and extent of a lesion. The choice of imaging technique varies depending on the infection’s location.
Computed Tomography Scan (CT Scan)
The degree of bone destruction is imaged most effectively on a CT scan. Vertebral osteomyelitis can destroy the vertebral body and cause spinal deformity (usually kyphosis). By reviewing the degree of bony destruction, the amount of spinal instability may be determined and can aid in deciding between non-surgical and surgical treatment options.
Magnetic Resonance Imaging (MRI)
MRI with and without gadolinium contrast enhancement has become the gold standard in identifying spinal infection, along with assessing the neural elements. MRI allows for the visualization of soft tissues that include the spinal cord, nerves, and paraspinal muscles, and adjacent soft tissue around the spinal column. Enhancement of the vertebral body, disc space, or epidural space is a key sign of infection; however, other pathologies such as tumors or inflammation must be ruled out.
Spinal infections usually require long-term intravenous antifungal or antibiotic therapy and can equate to extended hospitalization time for a patient. Immobilization can be recommended when a significant pain or the potential for spine instability is present. If the patient is neurologically and the spinal column is structurally stable, antibiotic treatment may be administered after the organism instigating the infection is properly labeled. Patients generally undergo antimicrobial therapy for a minimum of 6-8 weeks. The type of medication is determined on a basis that varies per case, depending on the patient’s specific circumstances (including his or her age).
Nonsurgical treatment should be considered initially when patients present minimal to no neurological deficits and the morbidity and mortality rates of surgery are high. However, surgery may be indicated when any of the following situations are present:
- Significant bone destruction instigating spinal instability
- Neurological deficits
- Sepsis with clinical toxicity started by an abscess unresponsive to antibiotics
- Failure of needle biopsy to obtain needed cultures
- Failure of intravenous antibiotics to eradicate the infection
Primary goals of surgery are to:
- Debride (clean and remove) infected tissue
- Enable infected tissue to receive adequate blood flow, helping to promote healing
- Restore spinal stability through the use of instrumentation to fuse the unstable spine
- Restore function or limit the degree of neurological impairment
Once it is determined that the patient requires surgery, imaging tools like x-rays, CT scans, or MRI can help further pinpoint the level at which to perform surgery.
Follow-up is essential to ensure that the spinal infection has been controlled and is responding to the treatment protocol. Repeat lab work and imaging studies will reflect improvement in the infection. CT and x-ray studies allow the surgeon to evaluate the integrity of the spine’s bony structures and ensure that spinal instrumentation has not failed.
Current treatment protocols for spinal infections require treatment by a multidisciplinary team of physicians, including infectious disease experts, neuroradiologists, and spine surgeons. The team will assess the best treatment approach on an individualized basis.