SPINAL INFECTIONS

Infection can be caused by bacterial or fungal organisms and can also occur after surgery. Most postoperative infections occur between three days and three months after surgery. Spinal infections can be classified according to their anatomical location:

• Spinal bone infections (osteomyelitis);
• Intervertebral disc space infections (discitis);
• Spinal canal infections (epidural abscess);
• Adjacent soft tissue infections.

Vertebral osteomyelitis is the most common form of vertebral infection. It can develop from direct open spine injury, surrounding infections, and bacteria spreading to the vertebrae.

Intervertebral disc 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 involve infections developing around the dura (the tissue surrounding the spinal cord and nerve root). Subdural abscess is much rarer and affects the potential space between the dura and arachnoid (thin membrane of the spinal cord, between dura mater and pia mater). Infections in the spinal parenchyma (primary tissue) are called intramedullary abscesses.

Adjacent soft tissue infections. Soft tissue infections usually affect younger patients and are not commonly seen in the elderly.

PREVALENCE AND INCIDENCE

• Spinal osteomyelitis affects approximately 26,170 to 65,400 people annually.
• Epidural abscess is rare, affecting only 0.2 to 2 cases per 10,000 hospital admissions. However, 5 to 18 percent of patients with vertebral osteomyelitis or disc space infection caused by adjacent spread will develop an epidural abscess.
• Some studies show that the frequency of spinal infections is increasing. This jump may be related to the increased use of vascular devices and other forms of instrumentation, and increased intravenous drug use.
• Approximately 30-70% of vertebral osteomyelitis patients have no obvious infection prior to the spinal infection.
• Epidural abscess can occur at any age, but is most common in people aged 50 and older.
• Although treatment has improved significantly in recent years, the mortality rate of spinal infections is still estimated at 20 percent.

Risk factors for spinal infection include conditions that compromise the immune system:

• Advanced age;
• Intravenous drug use;
• Human immunodeficiency virus (HIV) infection;
• Long-term systemic use of steroids;
• Diabetes;
• Organ transplant;
• Nutritional disorders;
• Cancer;

Surgical risk factors include prolonged operation time, high blood loss, use of instrumentation, and repeated or revision surgeries in the same area. Infections occur in 1-4% of surgical cases, despite numerous preventive measures followed.

CAUSES

Spinal infections can be caused by bacterial or fungal infections in another part of the body that are carried to the spine through the bloodstream. The most common source of spinal infections is a bacterium called Staphylococcus aureus, followed by Escherichia coli.

Spinal infections can occur after a urological procedure because the veins in the lower spine pass through the pelvis. The most commonly affected area of the spine is the lumbar region. Intravenous drug users are more prone to infections affecting the cervical region.

Intervertebral disc infections probably start in one of the adjacent endplates, and the disc is secondarily infected. There is some controversy regarding the origin in children. In children, most biopsy cultures are negative, and experts believe that childhood discitis may not be an infectious condition, but may result from partial displacement of the epiphysis (the growth zone near the end of the bone) as a result of compaction.

SYMPTOMS

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

• Mucus drainage from the wound
• Redness, swelling or tenderness near the incision
• Severe back pain
• Fever and chills
• Weight loss
• Muscle cramps
• Painful or difficult urination
• Neurological deficits

Intervertebral disc infections

At first, patients may show few symptoms, but eventually they develop severe back pain. Generally, young pre-verbal children do not have fever but suffer from back pain. Children aged 3 to 9 years usually present with back pain as the predominant symptom.

Disc space infection after surgery occurs on average one month after the operation. Pain is usually relieved by bed rest and immobilization, but increases with movement. If left untreated, the pain becomes worse and refractory, not even responding to pain medications.

Spinal canal infections

Adult patients usually progress through the following clinical stages:

• Severe back pain with fever and local tenderness in the spine
• Nerve root pain radiating from the infected area
• Muscle weakness and bowel / bladder dysfunction
• Paralysis

In children, the most prominent symptoms are prolonged crying, obvious pain in the palpated area, and hip pain.

Adjacent soft tissue infections

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

DIAGNOSIS

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

Laboratory tests

Specific laboratory tests can be useful for diagnosing spinal infections. It can be useful to perform blood tests for acute phase reactants, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels. Both ESR and CRP tests are usually good indicators of whether there is any inflammation in the body (the higher the level, the more likely there is inflammation). However, these tests are limited and other diagnostic tools are usually required.

Identification of the organism is important, and this can be achieved via biopsy of the spine or disc space under computerized tomography guidance. Blood cultures, preferably taken during a fever, can also help identify the pathogen involved in the spinal infection.

Imaging tools

Imaging studies are required to determine the location and extent of the lesion. The choice of specific imaging methods varies depending on the location of the infection. Soft tissue involvement is best determined by magnetic resonance imaging (MRI), while the degree of bone destruction is best assessed by computerized tomography (CT) scan.

TREATMENT

Non-surgical treatment

Spinal infections often require long-term intravenous antibiotic or antifungal therapy, which may equate to an extended hospital stay for the patient. Immobilization may be recommended when there is significant pain or potential for spinal instability. If the patient is neurologically and structurally stable, antibiotic treatment should be administered after the infecting organism has been properly identified. Patients usually 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 specific circumstances, including the patient’s age.

Surgical treatment

Non-surgical treatment should be considered first when patients have minimal or no neurological deficit, as the morbidity and mortality of surgical intervention are high. However, surgical intervention may be indicated when any of the following situations occur:

• Significant bone involvement;
• Neurological deficits;
• Abscess, systemic sepsis with clinical toxicity that does not respond to antibiotics;
• Inability to obtain necessary cultures via needle biopsy;
• Failure of intravenous antibiotics to eradicate the infection;

The goals of the operation are:

• Debride (clean and remove) the infected tissue;
• Ensure the infected tissue receives appropriate blood flow to aid healing;
• Maintain or restore spinal stability;
• Limit the degree of neurological damage;