For most people, a spine infection is caused when an infection or illness somewhere else in the body is carried through the blood stream into a disc in the spinal column. The infection may stay in the disc even after the illness has improved and eventually spread into vertebral bones, causing pain and deformity.
Discitis refers to an infection of the disc in the spine [Figure 1]. Osteomyelitis refers to an infection of the vertebral bone in the spine. Generally infections are spread to the spine by a vascular route. Bacteria may spread through the blood stream into the vertebral discs and affect this area. As the infection progresses, the disc space may be degenerated, closing down the disc space, and in some cases causing compression of a nerve leading to pain or numbness. As the disc decay progresses, the infection may spread into the vertebral bodies (bone), above and below the disc [Figure 2]. The bone, weakened by the infection may also begin to collapse or crumble as the infection progresses. In some cases the infection or crumbling bones may push into the area for the nerves or spinal cord which may cause neurologic symptoms including numbness, weakness, tingling, pain, or bowel or bladder dysfunction.
Figure 1: Discitis refers to an infection of the disc in the spine.
Figure 2: MRI of the lumbar spine showing an infection that started in the disc (discitis) and has spread into the vertebral bones above and below (osteomyelitis).
Conditions that weaken the immune system may predispose patients to spinal infection. These conditions include:
- Organ transplant
- Diabetes mellitus
- Use of immunosuppressant medications
- Intravenous drug abuse
Most spine infections occur in the lumbar spine because of the blood supply to this region of the spine. Infection from tuberculosis is rare in North America but when present is most commonly found in the thoracic spine. Infections associated with intravenous drug abuse are more likely to involve the neck or cervical spine.
The most common symptoms for patients with spinal infection include pain that develops slowly and steadily over an extended period of time. In addition to pain, patients may also complain of systemic illness such as fevers, chills, night pain, or unexplained weight loss. Some patients experience symptoms for a number of weeks or months prior to being diagnosed with their infection. If spinal infection is suspected, laboratory evaluation and radiographic studies are appropriate.
Diagnosing a spinal infection usually starts with an x-ray. However, x-rays are usually normal in the first two to four weeks after an infection begins. Additional imaging studies including an MRI scan with enhancement of intravenous dye (gadolinium) may be important in the diagnosis of the infection. An MRI scan also allows for visualization of the neurologic structures that may be affected.
Laboratory studies including blood work should be obtained. Blood cultures may help to determine the organism causing the infection. However, blood cultures are positive in less than half of all cases. Certain other blood work including inflammatory markers may be helpful to establish the diagnosis of infection. For some patients a needle biopsy or open surgery is necessary to obtain cultures and determine the organisms responsible for infection.
Treatment for most spinal infections include a combination of intravenous antibiotic medications, bracing, and rest. The most common case of spinal infection is staphylococcus aureus which is a bacteria that typically exists on human skin.
Antibiotic treatment is usually required for four to six weeks. Bracing may be recommended to improve stability of the spine while the infection is healing.
Surgical treatment is necessary if the infection is causing pressure on the neural elements or if the infection cannot be controlled with antibiotics and bracing. Surgery is used to treat the infection, prevent worsening of spinal deformity, and relieve neurologic compression and improve pain.
As treatment progresses, repeat blood tests and x-rays are typically required to verify the infection is responding to treatment. All patients with suspected spinal infection should seek treatment and patients with symptoms of neurologic compromise should seek emergent evaluation.