Vertebral Osteomyelitis and Discitis

Overview

Vertebral osteomyelitis with discitis is an infection of the vertebral body and the adjacent intervertebral disc, typically referred to together as spondylodiscitis because infection commonly spreads between the two structures. In adults, the disc itself has no blood supply, so bloodborne bacteria usually seed the vertebral body first, specifically the metaphyseal region near the endplate, where segmental arteries form low-flow vascular arcades. The infection then erodes through the endplate, spreading into the disc and the neighboring vertebra.

The resulting inflammatory and destructive process can produce vertebral collapse, forward angulation of the spine (segmental kyphosis), fluid collections alongside or within the spinal canal (paravertebral and epidural abscesses), and, in advanced cases, mechanical instability. The condition is relatively uncommon, but its incidence has risen with an aging population, broader use of spinal hardware, and a growing number of people living with weakened immune systems or chronic illness. It affects men more often than women and follows a bimodal distribution, with peaks in childhood and again in older adulthood.

What causes it

The most common route of infection is hematogenous: bacteria travel through the bloodstream from another site in the body and lodge in the vertebral endplate. Staphylococcus aureus is the most frequently isolated organism. Other causative agents include gram-negative bacilli, streptococci, and coagulase-negative staphylococci. In endemic regions or among immunocompromised patients, Mycobacterium tuberculosis (Pott disease), Brucella, and fungal organisms are also implicated.

The lumbar spine is most frequently affected, followed by the thoracic and then the cervical regions, reflecting differences in regional blood flow and mechanical load. Major risk factors include:

• Intravenous drug use
• Diabetes mellitus
• Chronic kidney disease or hemodialysis
• Immunosuppression from corticosteroids, malignancy, or HIV
• Bacteremia from a distant source such as endocarditis, a urinary tract infection, or a skin and soft tissue infection
• Indwelling vascular catheters
• Prior spinal surgery or epidural instrumentation

Symptoms and warning signs

The classic presentation is insidious, gradually worsening back or neck pain that is worse at night and not relieved by rest, a pattern that itself constitutes a recognized red flag for spinal infection. Fever is present in only a minority of patients, so its absence does not rule out the diagnosis. On examination, the affected spinal segment is usually tender to direct pressure and the surrounding muscles may be in spasm, with reduced range of motion.

Constitutional symptoms (malaise, unexplained weight loss, and drenching night sweats) raise particular concern for a slow-growing or tuberculosis-related infection.

The most urgent feature is the development of a neurologic deficit. Progressive motor weakness, new sensory loss, or new loss of bladder or bowel control can result from an epidural abscess or vertebral collapse compressing the spinal cord or cauda equina. This is a surgical emergency requiring immediate imaging and decompression. Any combination of spinal pain with fever, a neurologic change, immunosuppression, or known bacteremia should prompt rapid evaluation rather than empirical conservative management.

How it's diagnosed

Diagnosis requires combining clinical suspicion with laboratory markers, imaging, and microbiologic identification. No single test is definitive.

Blood tests: Inflammatory markers, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), are elevated in nearly all cases and serve both as diagnostic support and as benchmarks for monitoring treatment response. Blood cultures should be obtained in all suspected cases; they identify the causative organism in a meaningful proportion of patients.

Imaging: Contrast-enhanced MRI is the study of choice because of its high sensitivity and specificity. It reveals disc space narrowing, endplate erosion, marrow swelling (low T1 and high T2 signal in the vertebral body), and any paravertebral or epidural fluid collection. Plain X-rays are often normal early in the disease but may later show disc space loss and endplate irregularity. CT scanning better characterizes bony destruction and is used to guide percutaneous needle biopsy.

Tissue sampling: When blood cultures are negative, image-guided needle biopsy to obtain a microbiologic and histologic specimen is strongly recommended before antibiotics are started, provided the patient is clinically stable. Identifying the specific organism is essential for prescribing the right targeted therapy.

Treatment options

Treatment is predominantly medical. The cornerstone is prolonged organism-directed antibiotic therapy, typically administered for approximately six weeks and tailored to culture and susceptibility results. Broad-spectrum empirical antibiotics are started immediately only in patients who are hemodynamically unstable or septic and cannot safely wait for biopsy results.

Response is tracked clinically and through serial measurements of CRP and ESR, which should trend downward with effective treatment; routine repeat imaging is not used to judge progress. External bracing may be added to relieve pain and provide spinal support in selected patients.

When surgery is considered

Surgery is not the primary treatment, but it is indicated in the following circumstances:

• Significant or progressive neurologic deficit
• A symptomatic epidural or paravertebral abscess that is not amenable to percutaneous needle drainage
• Spinal instability or deformity resulting from bony destruction
• Failure of appropriately selected antibiotic therapy despite adequate duration
• Need for tissue sampling when less-invasive methods have not yielded a diagnosis

Operative goals include decompression of neural elements, debridement of infected and necrotic tissue, and, when the spinal column is structurally compromised, reconstruction with stabilization. Surgery is followed by a continued course of antibiotics. With timely diagnosis and appropriate treatment most patients recover; however, delays in diagnosis, virulent organisms, and established neurologic injury at the time of treatment are associated with worse functional outcomes.