Spinal infections are an important but relatively uncommon cause of back pain.

Clinical presentation

Patients may present with back pain, fevers, or neurological deficit. Disease progression normally is insidious and non-traumatic onset with constant non-position-dependent pain ¹.  

Risk factors

• intravenous drug use

• immunocompromised state

• prior instrumentation 

Pathology

Common infectious organisms

• most common: Staphylococcus aureus in more than 50% of cases and enteric gram-negative bacilli (e.g. Escherichia coli)

• diabetes: Streptococcal species

• IVDU: Gram-negative bacilli such as Pseudomonas and Candida

• immigrant population: Mycobacterium tuberculosis

• patients with sickle cell disease: Salmonella

Mechanism 

An infective agent can be introduced via the following ²: 

1. haematogenous

   • antegrade flow via nutrient arterioles

   • retrograde flow via the paravertebral Batson venous plexus

2. direct inoculation

Location

Three possible anatomical spaces that may be affected in spinal infections are ³:

• disk-endplate complex: producing discitis-osteomyelitis

• facet joints: producing septic arthritis

• epidural space: producing an epidural abscess

Vertebral infection commonly originates in the anterior endplate (due to its rich arterial supply), and therefore affects the psoas muscle before affecting paraspinous soft tissue including the epidural space.

Radiographic features

MRI

Signs of infection on non-contrast MRI ^3,4: 

• vertebral body T1 hypointensity

• vertebral body and disc T2 hyperintensity

• endplate destruction

• psoas sign: non-enhanced T2 hyperintensity in iliopsoas muscle - considered a key sign of early spondylodiscitis 

• epidural phlegmon