An infection in the spine is rare. When it does occur, it is not uncommon for the diagnosis to be delayed as the usual presenting symptom is of back pain and there may be little to distinguish it from “non-specific back pain”. The infection develops in the disc space and causes destruction of the bony end plates of either vertebra above and below the affected disc. This infection is called a discitis. The back pain is generally severe and persistent and the diagnosis should be considered in any patient who has been generally unwell or if they have signs of infection, such as a fever. The commonest source of infection is direct spread through the blood system, often from an unknown site. Patients who are very old or who are chronically ill, particularly with immuno-deficiency, are at greatest risk. Patients with diabetes are more at risk of infection.
If unchecked the infection can spread into the tissues to either side of the spine, or may even track into the neural canal and can cause compression of the spinal cord in the upper spine or the cauda equina in the lower spine. If the infection tracks into the neural canal and epidural space it becomes an epidural abscess. A variety of organisms can cause discitis but the commonest is Staphylococcus Aureus.
Discitis will often cause a raise in the white cell count and an elevation of the erythrocyte sedimentation rate (ESR). Plain x-rays can show an initial swelling of the disc height followed by a loss of disc height and loss of definition of the vertebral endplates. An MRI scan is the most reliable test for a discitis. This will show changes to the vertebral endplates with often spread of infection to the para-spinal tissues and into the epidural space. A sample of fluid is often required prior to treatment with antibiotics in order to identify which organism is causing the problem.
The patient is usually rested in bed. Intravenous antibiotics are given and often antibiotics can be given into the infected disc space itself. The condition is monitored by serial blood tests looking at inflammatory markers (ESR and CRP) and the white cell count. Surgery is required if the infection is spreading in spite of adequate antibiotic treatment, or if an abscess is causing direct pressure on the nerves (epidural abscess), or if another collection is locked in the tissues (abscess). Occasionally bony destruction can result following a disc infection leading to deformity and surgery may then be required.
Another type of spinal infection can be caused by the tuberculosis bacteria. Tuberculosis is an infection caused by bacteria which usually starts in the chest and spreads to other sites in the body. Throughout the world, the infection is extremely common, and particularly in developing countries. The condition is being seen more commonly in the United Kingdom, largely due to immigration. Infection usually settles in the part of the vertebra adjacent to the intervertebral disc. It causes destruction of the bone and spreads to the disc space and adjacent vertebra. The bone destruction can eventually lead to collapse of the spine and deformity. If this occurs then there is a serious risk of spinal cord damage and urgent treatment is required.