Why are patients with end-stage renal disease (ESRD) on hemodialysis (HD) at increased risk of developing spondylodiscitis?

Why Hemodialysis Patients Develop Spondylodiscitis

Hemodialysis patients develop spondylodiscitis primarily through hematogenous seeding from bacteremia originating at their vascular access sites, with central venous catheters carrying approximately 3 times higher risk than arteriovenous fistulas. 1

Primary Mechanism: Hematogenous Spread from Vascular Access

The major route of infection is hematogenous, with the venous access being the most likely source of bacteremia that seeds the vertebral column 1. This occurs through the following pathway:

• Vascular access infection or colonization leads to bacteremia, which then disseminates to the highly vascular vertebral bodies and intervertebral discs 1, 2
• Staphylococcus aureus is the predominant pathogen (identified in 62-89% of cases), which has particular tropism for bone and disc tissue 1, 2, 3
• The vertebral venous plexus (Batson's plexus) provides a direct route for bacterial seeding from systemic circulation to the spine 1

Critical Risk Factors Specific to Hemodialysis

Vascular Access Type and History

• Central venous catheters (CVCs) increase risk 3-fold compared to arteriovenous fistulas, with incidence approximately 3 times higher in patients dialyzing with tunneled CVCs 1
• Multiple vascular access procedures in a patient's history significantly increases risk, as each access creation or revision represents a potential source of bacteremia 2
• 22.2% of spondylodiscitis cases are directly associated with vascular access infections 4
• Access problems, particularly CVC infections, are common in the months preceding spondylodiscitis onset, and CVC removal during these episodes does not necessarily prevent progression to spondylodiscitis 1

Immunocompromised State

• Uremia-induced immune dysfunction impairs neutrophil function, cell-mediated immunity, and antibody responses, making ESRD patients inherently susceptible to infections 1, 2
• Multiple comorbidities are typical, with affected patients being elderly (mean age 64.9-70 years) and having diabetes (50%), cardiovascular disease (55.6%), and other conditions that further compromise immune function 1, 4

Dialysis-Specific Factors

• Longer renal replacement therapy (RRT) duration correlates with increased risk of metastatic infection including spondylodiscitis 5
• 44.4% of patients who developed spondylodiscitis started hemodialysis within 1 year prior to infection, suggesting the early dialysis period carries particular vulnerability 4
• Elevated CRP levels at admission are significantly correlated with development of metastatic infection from catheter-related bloodstream infections 5

Anatomical Predisposition

• Pre-existing degenerative spinal disease is present in 61% of hemodialysis patients who develop spondylodiscitis, potentially providing sites of reduced vascular flow where bacteria can more easily establish infection 4
• Lumbar hernia presence is associated with increased risk of metastatic spondylodiscitis in the setting of catheter infection 5
• The lumbar region is the most common location (77.8% of cases), likely due to increased mechanical stress and blood flow to this area 4

Bacteremia Rates by Access Type

The Canadian Society of Nephrology guidelines document that bacteremia rates vary dramatically by access type 6, 7:

• CVCs: 0-19 per 100 patient-years with infection rates of 1.6 per 1,000 catheter-days for tunneled catheters 7
• AVFs/AVGs: 0-11 per 100 patient-years with significantly lower systemic infection risk 6, 7
• Buttonhole cannulation (when used) has infection risk comparable to tunneled CVCs, with the majority of buttonhole-related systemic infections being S. aureus associated with metastatic complications including vertebral osteomyelitis 6

Clinical Implications

The incidence of spondylodiscitis in hemodialysis patients is approximately 1 episode per 215 patient-years, which is substantially higher than the general population 1. The mortality rate ranges from 16.7% to 46%, with death predicted by development of complications and pre-existing cardiovascular comorbidity 1, 3, 4.

Prevention Strategy

Limiting CVC use and prioritizing arteriovenous access should be the overriding preventive aim, as strategies to reduce bacteremia prevalence directly reduce spondylodiscitis risk 1. The Canadian Society of Nephrology recommends arteriovenous access (AVF or AVG) over tunneled CVCs specifically to prevent the increased infection risk 6.

When CVCs must be used, strict adherence to infection control measures including chlorhexidine-alcohol skin preparation, catheter hub disinfection with antiseptic every time the catheter is accessed, and maximal sterile barrier precautions are essential 8.