Spinal Infection (Discitis)

What is it?

Spinal infection is a general term that includes several closely related conditions affecting different parts of the spine. Discitis is infection of an intervertebral disc, typically starting in the bone next to the disc and spreading into the disc itself. When the infection involves both the disc and the adjacent vertebrae, it is called spondylodiscitis. Vertebral osteomyelitis refers specifically to infection within the bone of a vertebra. Infection can also collect outside the dura within the spinal canal as an epidural abscess, or in nearby soft tissues such as the paraspinal muscles.

Most spinal infections are caused by bacteria, with Staphylococcus aureus being the most common organism. Less commonly, other bacteria, mycobacteria (such as tuberculosis), or fungi can be responsible. Infection most often reaches the spine through the bloodstream from another site—such as a urinary tract infection, skin infection, or endocarditis—but can also occur after spinal injections, surgery, or, less commonly, by direct spread from nearby infection. Risk factors include older age, diabetes, intravenous drug use, immune suppression, chronic kidney disease, cancer, recent spinal procedures, and prolonged use of indwelling catheters or central lines.

Symptoms often develop gradually over weeks. The most common is persistent, focal back or neck pain that may be present at rest and tends to be worse at night—an important departure from typical mechanical back pain, which usually improves with rest. Fever and chills are common but not always present, particularly in older adults. Local tenderness over the affected area of the spine is often noted on examination. If the infection involves the spinal canal or compresses nearby nerves or the spinal cord, neurological symptoms such as numbness, tingling, weakness, gait difficulty, or bowel or bladder dysfunction may develop. Epidural abscess is a particularly important diagnosis because it can progress to severe neurological injury if not recognized and treated promptly.

MRI of the spine with contrast is the preferred imaging test for evaluating suspected spinal infection because it provides detailed views of the discs, vertebrae, epidural space, and surrounding soft tissues, and it is highly sensitive for the changes of infection. Typical findings include increased fluid signal in the disc and adjacent vertebrae, contrast enhancement, and sometimes an associated abscess. CT may be useful when MRI is not possible and for evaluating bony detail. Blood tests for inflammatory markers (such as CRP, ESR, and white blood cell count) and blood cultures support the diagnosis. Image-guided needle biopsy or surgical sampling is often performed to identify the specific organism and guide antimicrobial therapy.