Spinal Infections

OVERVIEW

Spinal infections can be classified by the anatomical location involved: the vertebral column, intervertebral disc space, the spinal canal and adjacent soft tissues. Infection may be caused by bacteria or fungal organisms and can occur after surgery. Most postoperative infections occur between three days and three months after surgery.

Vertebral osteomyelitis is the most common form of vertebral infection. It can develop from direct open spinal trauma, infections in surrounding areas and from bacteria that spreads to a vertebra from the blood.

Intervertebral disc space infections involve the space 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, which is an infection that develops in the space around the dura (the tissue that surrounds the spinal cord and nerve root). Subdural abscess is far rarer and affects the potential space between the dura and arachnoid (the thin membrane of the spinal cord, between the dura mater and pia mater). Infections within the spinal cord parenchyma (primary tissue) are called intramedullary abscesses.

Adjacent soft-tissue infections include cervical and thoracic paraspinal lesions and lumbar psoas muscle abscesses. Soft-tissue infections generally affect younger patients and are not seen often in older people.

Incidence and Prevalence

• Vertebral osteomyelitis affects an estimated 26,170 to 65,400 people annually.
• Epidural abscess is relatively rare, with 0.2 to 2 cases per every 10,000 hospital admissions. However, 5-18% of patients with vertebral osteomyelitis or disc space infection caused by contiguous spread will develop an epidural abscess.
• Some studies suggest that the incidence of spinal infections is now increasing. This spike may be related to increased use of vascular devices and other forms of instrumentation and to a rise in intravenous drug abuse.
• About 30-70% of patients with vertebral osteomyelitis have no obvious prior infection.
• Epidural abscess can occur at any age, but is most prevalent in people age 50 and older.
• Although treatment has improved greatly in recent years, the death rate from spinal infection is still an estimated

Risk factors for developing spinal infection include conditions that compromise the immune system, such as:

• Advanced age
• Intravenous drug use
• Human immunodeficiency virus (HIV) infection
• Long-term systemic usage of steroids
• Diabetes mellitus
• Organ transplantation
• Malnutrition
• Cancer

Surgical risk factors include surgeries of long duration, high blood loss, implantation of instrumentation and multiple, or revision, surgeries at the same site. Infections occur in 1-4% of surgical cases, despite numerous preventative measures that are followed.

Causes

Spinal infections can be caused by either a bacterial or a fungal infection in another part of the body that has been carried into the spine through the bloodstream. The most common source of spinal infections is a bacterium called staphylococcus aureus, followed by Escherichia coli.

Spinal infections may occur after a urological procedure, because the veins 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 prone to infections affecting the cervical region. Recent dental procedures increase the risk of spinal infections, as bacteria that may be introduced into the bloodstream during the procedure can travel to the spine.

Intervertebral disc space infections probably begin in one of the contiguous end plates, and the disc is infected secondarily. In children, there is some controversy as to the origin. Most cultures and biopsies in children are negative, leading experts to believe that childhood discitis may not be an infectious condition, but caused by partial dislocation of the epiphysis (the growth area near the end of a bone), as a result of a flexion injury.

Symptoms

Symptoms vary depending on the type of spinal infection but, generally, pain is localized initially at the site of the infection. In postoperative patients, these additional symptoms may be present:

• Wound drainage
• Redness, swelling or tenderness near the incision

Vertebral Osteomyelitis

• Severe back pain
• Fever
• Chills
• Weight loss
• Muscle spasms
• Painful or difficult urination
• Neurological deficits: weakness and/or numbness of arms or legs, incontinence of bowels and/or bladder

Intervertebral Disc Space Infections

Patients may initially have few symptoms, but eventually develop severe back pain. Generally, younger, preverbal children do not have a fever nor seem to be in pain, but they will refuse to flex their spines. Children age three to nine typically present with back pain as the predominant symptom

Postoperative disc space infection may be present after surgery, occurring, on average, one month after surgery. The pain is usually alleviated by bed rest and immobilization, but increases with movement. If left untreated, the pain gets progressively worse and intractable, unresponsive even to prescription painkillers.

Spinal Canal Infections

Adult patients often progress through the following clinical stages:

1. Severe back pain with fever and local tenderness in the spinal column
2. Nerve root pain radiating from the infected area
3. Weakness of voluntary muscles and bowel/bladder dysfunction
4. Paralysis

In children, the most overt symptoms are prolonged crying, obvious pain when the area is palpated and hip tenderness.

Adjacent Soft-tissue Infections

In general, symptoms are usually nonspecific. If a paraspinal abscess is present, the patient may experience flank pain, abdominal pain or a limp. If a psoas muscle abscess is present, the patient may feel pain radiating to the hip or thigh area.

When & How to Seek Medical Care

Seek medical care if symptoms of a spinal infection are present. Early diagnosis and treatment can prevent progression of the infection and may limit the degree of intervention required to treat the infection. Delaying care may result in progression of the infection causing 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, such as weakness of arms or legs and/or bowel/bladder incontinence.
• Fever not controlled with medication.

Diagnosis

The biggest challenge is making an early diagnosis before serious morbidity occurs. Diagnosis typically takes an average of one month, but can take as long as six months, impeding effective and timely treatment. Many patients do not seek medical attention until their symptoms become severe or debilitating.

Laboratory Tests

Specific laboratory tests can be useful in helping to diagnose a spinal infection. It may be beneficial to get blood tests for acute-phase proteins, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels. Both ESR and CRP tests are often good indicators as to whether any inflammation is present in the body (the higher the level, the more likely it is that inflammation is present). As inflammation is the body’s natural response to infection, these markers can monitored to assess the presence of infection and the effectiveness of treatment. These tests alone however, are limited, and other diagnostic tools are usually required.

Identification of the organism is essential, and this can be accomplished through computed tomography-guided biopsy sampling of the vertebra or disc space. Blood cultures, preferably taken during a fever spike, can also help identify the pathogen involved in the spinal infection. Proper identification of the of the pathogen is necessary to narrow the antibiotic treatment regiment.

Imaging Tools

Imaging studies are necessary to pinpoint the location and extent of a lesion. The choice of specific imaging techniques varies slightly, depending on the location of the infection.

Computed Tomography Scan (CT Scan)

The degree of bone destruction is best imaged on a CT scan. Vertebral osteomyelitis can destroy the vertebral body and lead to spinal deformity (typically kyphosis). By assessing the degree of boney destruction, the amount of spinal instability can be determined and can aid in deciding between non-surgical and surgical treatment options.

The CT scan above shows vertebral osteomyelitis at L3-L4 resulting in destruction of the L3 and L4 vertebral bodies. The second CT shows a thoracic spinal compression fracture due to osteomyelitis causing a kyphotic deformity of the spine.

Magnetic Resonance Imaging (MRI)

MRI with and without gadolinium contrast enhancement has become the gold standard in identifying spinal infection and assessing the neural elements. MRI allows for visualization of the soft tissues that include the nerves, spinal cord, 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 inflammation or tumors must be ruled out.

Surgical Treatment

Spinal infections often require long-term intravenous antibiotic or antifungal therapy and can equate to extended hospitalization time for the patient. Immobilization may be recommended when there is significant pain or the potential for spine instability. If the patient is neurologically and the spinal column is structurally stable, antibiotic treatment should be administered after the organism causing the infection is properly identified. Patients generally undergo antimicrobial therapy for a minimum of six to eight weeks. The type of medication is determined on a case-by-case basis depending on the patient’s specific circumstances, including his or her age.

Surgical Treatment

Nonsurgical treatment should be considered first when patients have minimal or no neurological deficits and the morbidity and mortality rate of surgical intervention is high. However, surgery may be indicated when any of the following situations are present:

• Significant bone destruction causing spinal instability
• Neurological deficits
• Sepsis with clinical toxicity caused by an abscess unresponsive to antibiotics
• Failure of needle biopsy to obtain needed cultures
• Failure of intravenous antibiotics alone to eradicate the infection

The primary goals of surgery are to:

• Debride (clean and remove) the infected tissue
• Enable the infected tissue to receive adequate blood flow to help promote healing
• Restore spinal stability with 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 such as plain x-rays, CT scans or MRI can help further pinpoint the level at which to perform surgery.

Follow-Up

Proper and timely follow-up is necessary to ensure that the spinal infection has been controlled and is responding to the treatment protocol. Repeat lab work and imaging studies should reflect improvement in the infection. CT and x-ray studies will allow the surgeon to assess the integrity of the boney structures of the spine 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 be able to assess the best treatment approach on an individualized basis, whether it is surgical or nonsurgical.

Case Example: Osteomyelitis of L3 and L4 vertebral bodies

MRI (left) and CT (middle) scan showing osteomyelitis of the L3 and L4 vertebral bodies causing destruction of the spinal column. This leads to spinal instability and compression of the lumbar nerve roots. Patient underwent surgery for debridement of the L3 and L4 vertebral bodies and implantation of a titanium graft, pedicle screws, and rods to reconstruct the spinal column (right).