A spinal infection occurs when microorganisms invade the tissues of the vertebral column or its surrounding structures. These infections are relatively uncommon but can cause significant damage to the bones, discs, and nerves of the spine if not promptly recognized and treated. The pathogens responsible are typically bacteria, though fungi and, rarely, viruses may also be the cause. A suspected spinal infection is considered a medical urgency requiring immediate attention.
Where Infections Occur in the Spine
Spinal infections are classified based on the specific anatomical structure they affect. One of the most common forms is vertebral osteomyelitis, an infection localized to the vertebral body, the dense bone segment that bears weight. This condition causes destruction and softening of the bone tissue, which can lead to fractures or spinal instability.
Another common location is the intervertebral disc space, an infection known as discitis. The discs are the soft, cushion-like structures situated between the vertebrae. Discitis is seen more frequently in children and adolescents, though it also occurs in adults. When both the vertebral body and the adjacent disc are involved, the condition is referred to as spondylodiscitis.
Infections can also develop within the spinal canal, most often presenting as a spinal epidural abscess (SEA). This occurs when a collection of pus forms in the epidural space, situated between the outer membrane of the spinal cord (dura mater) and the bone of the vertebrae. An abscess in this confined space can exert pressure on the spinal cord and nerve roots, leading to neurological symptoms. This type of infection often occurs in combination with vertebral osteomyelitis.
How Spinal Infections Start
Spinal infections begin when a pathogen gains entry into the spinal structures through one of three primary routes. The most frequent mechanism is hematogenous spread, where microorganisms travel through the bloodstream from a distant site of infection in the body. For instance, bacteria from a common skin or urinary tract infection can settle in the highly vascularized bone of the vertebrae.
The most common causative agent is the bacterium Staphylococcus aureus, which is responsible for the majority of pyogenic (pus-forming) spinal infections. Other organisms like Escherichia coli and various fungi can also be involved, particularly in individuals with compromised immune systems. Once lodged in the spine, the pathogen multiplies, leading to a local inflammatory process.
Certain pre-existing conditions and recent procedures increase an individual’s susceptibility to developing a spinal infection. Risk factors include:
- A weakened immune response due to conditions like diabetes, HIV/AIDS, or cancer.
- Long-term steroid therapy.
- Intravenous drug use.
- Recent spinal surgery or procedures like epidural injections, which can introduce bacteria directly (direct inoculation).
Infections can also spread contiguously, moving from an adjacent infected soft tissue into the spine.
Recognizing the Physical Signs and Confirming Diagnosis
The initial signs of a spinal infection can be vague and develop slowly over weeks or even months, often delaying diagnosis. The most consistent symptom is severe, localized back pain, which is unresponsive to common pain relievers and often worsens at night or with movement. This pain may be accompanied by systemic signs of infection, such as fever and chills.
As the infection progresses, it can cause structural damage or lead to the formation of an abscess that compresses the spinal cord or nerve roots. This compression can manifest as new neurological deficits, including weakness, numbness, or tingling in the limbs. In advanced cases, patients may experience difficulty walking or the loss of bowel and bladder control, which signals a medical emergency.
To confirm a spinal infection, clinicians rely on a combination of blood tests and advanced imaging. Blood work reveals elevated levels of inflammatory markers, specifically the Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP). Blood cultures are also performed to isolate the specific causative microorganism.
Magnetic Resonance Imaging (MRI) is considered the gold standard for diagnosis, as it provides detailed images of the bone, discs, and soft tissues. The MRI can locate the infection, determine the extent of bone and disc destruction, and identify any abscesses putting pressure on the spinal cord. In some cases, a needle biopsy or aspiration is performed under image guidance to obtain tissue or fluid. This allows for identification of the pathogen and guides the selection of the most effective antibiotic.
Medical Management and Recovery
The mainstay of treatment for most spinal infections is a prolonged course of targeted antimicrobial therapy. Once the specific organism is identified through biopsy or culture, an infectious disease specialist selects the appropriate intravenous antibiotic or antifungal medication. This initial therapy is often administered in the hospital and is continued for several weeks, sometimes transitioning to oral antibiotics.
Surgical intervention is reserved for cases where non-operative treatment is insufficient or when complications arise. Surgery may be needed to drain a large abscess or to relieve pressure on the spinal cord caused by the infection. Procedures are also necessary to debride (remove) necrotic or infected tissue and to stabilize the spine if the infection has caused significant bone destruction and instability.
Recovery from a spinal infection is often a lengthy process. Patients are often required to wear a brace or use other forms of immobilization to support the spine while the damaged bone and tissue heal. Physical therapy helps patients regain strength, flexibility, and mobility that may have been compromised by the infection or subsequent surgery.