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