Pathology

• metaphyses & cartilaginous end plates - starting areas for blood-borne infections
• in adults > 30 years the intervertebral disc receives its nutrition from tissue fluids rather than from direct blood supply

Blood supply

• arterial supply to the vertebrae
• vertebral artery, intercostal artery, or lumbar arteries provide nutrient vessels that enter the vertebral body
• posterior spinal branch arteries enter the spinal canal through each neural foramen & separate into ascending and descending branches that anastomose with similar branches at each level
• intervertebral disc is centrally avascular & dependent on diffusion for its nutrition
• pelvic veins drain into the spinal venous plexus - frequent metastasis of pelvic tumours & infections to the spine

Mechanism

• iatrogenic infection - usually through surgical manipulation directly or percutaneously
• local spread from contiguous structures
• from the colon via subphrenic abscesses
• arterial spread of pyogenic bacteria
• most common method
• originates in the end plate of the vertebra or in the vertebral body itself
• spreads to the disc secondarily as the infection progresses
• bacterial infections rapidly attack the intervertebral disc
• TB & non bacterial infections preserve intervertebral disc

Aetiology

Organism

• Staphylococcus aureus & S.epidermidis most common in pyogenic infection (60%)
• increase in the resistant strains of the organism
• intravenous drug users commonly infected w/ Pseudomonas aeruginosa
• Mycobacterium tuberculosis is the most common nonpyogenic infecting agent

Cause

• spinal surgery is the most common cause of iatrogenic disc infection
• genitourinary infection most common predisposing factor for blood-borne infection
• respiratory and dermal infections are less frequently implicated
• decreased natural immune response
• diabetes, alcoholism, rheumatoid arthritis
• chronic renal disease
• AIDS

Site

• vertebral end plate > disc space > epidural abscess formation > paraspinal abscess
• thoracic & lumbar spinal vertebrae - most common areas of pyogenic infection
• thoracolumbar junction - TB

Diagnosis
Physical Examination

History

• recent infection is not uncommon
• immune-suppressing disease

Symptoms

• pain most common 85%
• w/ changes in position, ambulation
• intensity varies from mild to extreme
• other symptoms - anorexia, malaise, night sweat, intermittent fever & weight loss
• spinal deformity late presentation of the disease
• paralysis is complication - rarely is the presenting complaint

Signs

• temperature elevation usually minimal
• localised tenderness
• paraspinal spasm
• limitation of motion of the involved spinal segments
• torticollis
• bizarre posturing
• other possible findings
• Kernig's sign, hamstring spasm & generalised weakness
• abscess formation
• neurologic signs
• most frequent w/ infections in the cervical & thoracic areas

Investigations

Bloods

• FBC, diff.count
• ESR, CRP
• culture
• skin testing

X-ray

• from 2 weeks to 3 months after the onset of the infection
• disc space narrowing, vertebral end plate irregularity or loss of N contour of the end plate
• periosteal reaction & hypertrophic (sclerotic) bone formation
• paravertebral soft tissue masses
• late findings - vertebral collapse, segmental kyphosis & bony ankylosis

Radionuclide scanning

• effective in identifying spinal infection
• techniques include
• technetium 99 (Tc-99m) bone scan
• gallium 67 (Ga-67) scan
• indium 111-labelled leukocyte (In-111 WBC scan)
• false-positive results in neoplastic, non-infectious inflammatory lesions

Computed tomography

• identifies paravertebral soft tissue swelling & abscesses
• monitor changes in the size of the spinal canal
• findings w/ CT scanning are similar to those with plain roentgenograms
• lytic defects in the subchondral bone
• destruction of the end plate with irregularity or multiple holes
• post-myelogram CT
  • defines compression of the neural elements by abscess or bone impingement

MRI

• accurate & rapid method for identifying spinal infection
• identifies infected & normal tissues & best determines the full extent of the infection
• does not differentiate between pyogenic & nonpyogenic infections
• need for diagnostic biopsy

T1-weighted images

• << signal intensity in the vertebral bodies & disc spaces
• margin between the disc and the adjacent vertebral body cannot be differentiated

T2-weighted images

• signal intensity >> in vertebral disc & << in vertebral body
• paravertebral abscess - areas of increased uptake

Diagnostic biopsy

• best method of determining infection
• appropriate antibiotics can be administered
• administration of AB before biopsy may result in a negative biopsy
• needle biopsy w/ roentgenographic or CT scan control or open biopsy

Differential Diagnosis

• primary & metastatic malignancies
• metabolic bone diseases w/ pathologic fractures
• infections in contiguous & related structures
• psoas muscle, hip joint, abdominal cavity & genitourinary system
• R.A., ankylosing spondylitis & Charcot spinal arthropathy

Non operative treatment

• usual Rx
• bed rest & immobilisation
• body cast or removable body jacket
• antibiotic treatment
• according to the positive stains or MC/S
• time for discontinuing antibiotic therapy
• iv. antibiotics for about 6 weeks & followed by oral
• until the ESR returns to normal
• failure of improvement in the ESR or continued persistence of symptoms should initiate re-evaluation of the therapy, and possibly repeat biopsy or even open biopsy for cultures or to remove sequestered and infected material

Prognosis

• most spinal infections resolve symptomatically and roentgenographically w/in 9-24/12
• recurrence of the infection & periods of decreased immune response are always possible
• delayed complications of kyphosis, paralysis & myelopathy

Indications for surgery

• progressive neurology on conservative rx.
• instability of spinal column

Specific infections

Pyogenic Infections

• males > females
• adults > children
• peak ages between 45-65 years
• most common organism reported is S. aureus

Infections in children

• syndrome of discitis(vertebral osteomyelitis)
• average age of onset 6-7 yrs
• characterised by fever & >> ESR
• followed by disc space narrowing on plain X-rays
• frequently difficulty in walking, malaise, irritability
• most culture reports are positive for S. aureus
• in children younger than 6 years of age may be viral in origin

diagnosis difficult initially

• plain roentgenograms usually negative
• may be a mild febrile reaction, but patients do not appear systemically ill
• only an elevated ESR
• best test either MRI scanning or a combination of bone scanning & gallium scanning
• blood cultures helpful if obtained during the initial febrile period of the illness

treatment

• bed rest and immobilisation
• diagnosis confirmed w/ blood cultures - intravenous AB
• surgical procedures rarely are required

Disc space infection in adults

• in adults intervertebral disc avascular - can't occur by a blood-borne route

surgical manipulation

• incidence of disc space infection after disc surgery range from 1% to 2.8%
• after discography 1% w/ single-needle technique 0.5% with the double-needle tech
• infecting organism is S. aureus

diagnosis difficult and is almost always delayed

• pain most common complaint
• diagnostic studies - ESR, bone scan & gallium scan positive 4-6 weeks after surgery
• MRI the best way to identify
• biopsy - closed or open
• Rx: specific or empiric antibiotics

Epidural space infection

• low reported incidence - increased in immunosuppressed patients
• morbidity and mortality are high
• may complicate a primary disc space infection
• the infection frequently spans three to five vertebral segments, even whole canal
• S. aureus is the most common

clinical findings

• several distinct differences:
• a more rapid development of neurologic symptoms (days instead of weeks)
• a more acute febrile illness
• signs of meningeal irritation, including radicular pain w/ positive straight leg-raising test and neck rigidity
• MRI is critical to the determination
• treatment
• surgical drainage and appropriate antibiotic therapy

Brucellosis

• results in a noncaseating, acid-fast, negative granuloma
• caused by a gram-negative capnophilic coccobacillus
• individuals involved in animal husbandry and meat processing

symptoms

• polyarthralgia, fever, malaise, night sweats, anorexia & headache
• psoas abscesses are found in 12% of patients
• bone involvement, most frequently the spine, occurs in 2-30% of patients

X-ray

• steplike erosions of the margin of the vertebral body require 2 months to develop
• disc space thinning and vertebral segment ankylosis by bridging
• CT scans and MRI - may show soft tissue involvement
• brucella titers of 1:80 or greater; confirmatory cultures

treatment

• antibiotic therapy for 4 months and close monitoring of the brucella titers

Fungal infections

• noncaseating, acid-fast, negative infections
• usually occur as opportunistic infections in immunocompromised patients
• development of symptoms usually is slow
• pain is less prominent as a physical symptom than in other forms of spinal osteomyelitis
• laboratory and roentgenographic findings are similar to those of pyogenic infections

Diff.dg

• tubercular infection
• tumours
• direct culture by biopsy is the only method of absolute determination
• Aspergillus and cryptococcal infections are of special note