Before the use of antibiotics, 40% to 70% of the patients with infections of spine use to die. But advances in chemotherapy have dramatically altered the natural history of these diseases.
In modern times, infections of spine are relatively rare and account for about 2% to 4% of all osteomyelitis infections and the and mortality has come down to 1% to 20%.
One of the unique and serious complication of the spinal infection is paralysis and is reported to occur in 50% of patients with spinal infections.
Infections of Spine- Natural History
Blood-borne infections of spine probably begins in the capillary loop or postcapillary venous channels in the end plate. Slowing of the circulation leads to sludging which in turn is responsible for suppurative inflammation, tissue necrosis, bony collapse, and spread of the infection into the adjacent intervertebral disc spaces.
End plate erosions that are the first radiographic findings.
The infection can extend anteriorly to create a paravertebral abscess or posteriorly to cause an epidural abscess.
Similarly, epidural abscesses may cross the spinal epidural space and enter the meningeal space and spinal cord itself.
There may be associated neurological deficits due to
(2) secondary compression from pathological fracture as a result of bone softening.
The course of the infection varies with the infecting organism and the patient’s immune status.
Death occurs in 10% of patients with overwhelming spinal infections.
Individuals with a good immune response may overcome the infection with no treatment.
Spinal infection may result in early or late paralysis.
Factors that indicate an increased predisposition to paralysis in pyogenic and fungal [Not in tubercular] osteomyelitis-
- Higher vertebral level of infection
- The presence of debilitating disease, such as diabetes mellitus, rheumatoid arthritis or chronic steroid usage
- S. aureus infections
- Healing results in formation of fibrous tissue and/or bone
Clinical Presentation of Infections of Spine
Pain is the most common presenting symptom of infections of spine and the typical pain occurs with changes in position and activity. There are associated constitutional symptoms
Spinal deformity may be a late presentation of the disease. Paralysis is a serious complication, but rarely the presenting complaint.
On local examination localized tenderness, paraspinal spasm, limitation of motion of the involved spinal segments are indicators.
In cervical spine torticollis may be the presenting feature.
Elderly and immunosuppressed individuals may present with minimal symptoms
Abscess formation in spine is difficult to ascertain unless the abscess points out superficially.
Often these areas are away from the primary abscess because the abcess can trickle down on fascial planes to reach a place away from the original abscess.
For example it is common for a paraspinal abscess to present as a swelling in the groin because of extension along the psoas muscle.
There may be associated neurological deficit depending upon the region involved. The deficit is caused by abscess formation, bone collapse, or direct neural infection.
Imaging in Infections of Spine
Most common initial study in patients with spinal infection. Findings may include
- Disc space narrowing
- Vertebral end plate irregularity
- Loss of the normal contour of the end plate
- Defects in the subchondral portion of the end plate
- Sclerotic bone formation
- Paravertebral soft-tissue masses may be noted with involvement of nearby areas of the spine.
The radiological findings may take up to 2- months to develop.
Late radiographic findings may include vertebral collapse, segmental kyphosis, and bony ankylosis.
CT helps to identify paravertebral soft-tissue swelling and abscesses much more readily. Because it helps to monitor changes better, it is often used to determine clinical progress.
CT findings may include
- Lytic defects
- Destruction of the end plate
- Sclerosis near the lytic irregularities,
- Hypodensity of the disc
- Flattening of the disc
- Soft-tissue density in the epidural and paraspinal regions.
CT myelography helps to identify neural compression and whether the infection extends to the neural structures themselves.
Magnetic Resonance Imaging
MRI is a rapid and accurate method for identifying spinal infection and determine the full extent of the infection. It however does not differentiate between pyogenic and nonpyogenic infections
MRI findings may show
- Decreased signal intensity in the vertebral bodies and disc spaces in T1 Weighted images
- Increased signal intensity in the vertebral disc and is markedly decreased in the vertebral body in T2 weighted images
- Abscesses in the paravertebral soft tissue can be better visualized. Gadolinium-labeled diethylenetriaminepentaacetic acid enhanced images seem to enhance the delineation.
MRI also helps to identify infections of spinal cord like myelitis without epidural or bone involvement.
MRI is can be used to follow the progression of the treatment along with clinical parameters.
Following radionuclide studies are used in infections of spine
- Technetium-99m (99mTc) bone scan
- Gallium-67 (67Ga) scan
- Indium-111–labeled leukocyte (111In WBC) scan.
Bone scans are almost always positive in patients with infection, but they cannot be diagnostic of infection. The 67Ga scan is a good adjunct to bone scanning for the detection of osteomyelitis and in documentation of clinical improvement.
The 111In WBC scan can detect abscesses, but does not differentiate between acute and chronic infections.But it is able to differentiate between non infectious collections like hematomas.
Labortary studies that point towards infection are
- Raised erythrocyte sedimentation rate
- Elevation of C-reactive protein
It must be noted that all the above findings are generalized indicators and none of them is specific.
Needle biopsy of the lesion is the best but not foolproof method of determining infection and identifying the causative agent. Time, host resistance, bacterial virulence, prior antibiotic exposure, and culture of the proper part are factors in successful isolation of the organism.
Needle biopsy is frequently done under local anesthesia, with radiographic or CT control.
Erythrocyte Sedimentation Rate
The erythrocyte sedimentation rate is used both for evaluation and clinically monitor osteomyelitic disc space infection. Though it is found to be elevated in more than 70% of the children with vertebral infection, erythrocyte sedimentation rate only indicates an inflammatory process and is not diagnostic in itself.
The reading could be as high as >100 mm/h in some patients but in majority it is >50.
There are other instances when it can be found elevated. For example – Surgery.
When ESR is increased after surgery, it usually decreases to a nearly normal level at 4 weeks after surgery and persistent elevation beyond this period along with associated clinical findings, indicates a persistent infection.
C Reactive Protein
Elevation of C-reactive protein is an early indicator of infection and returns rapidly to normal with resolution of the infection. ESR takes much longer to return to normal. A raised CRP is again a non specific indicator of inflammation and its value should be
However longer time is required to obtain the results compared with the ESR.
Leukocyte Count [White Blood Cell Count]
Leukocytosis may be a feature in spinal infections but again it is not helpful in diagnosing spinal infection as White blood cell counts may decrease in infants and debilitated patients.
Moreover, raised white blood cell counts may indicate areas of infection other than the spine.
Blood cultures are helpful if positive. Positive blood culture results only when the blood sample is withdrawn at the time of acute febrile illness. A positive blood culture may be adequate for the diagnosis and treatment of osteomyelitis but it rarely happens.
This is important in HIV positive patients.It has been reported that spinal infection occurred when the CD4 count was >200/mL, while osteoarticular and soft-tissue infection occur present when the CD4 count was <200/mL. Some authors have even suggested CD4 count as a predictor of the clinical course. Patients with with a moderate decrease in the CD4 count (about 200/mL) whereas those with lower counts perform worse.
Treatment of Infections of Spine
Treatment of infections of spine must be be individualized. Broad-spectrum antibiotics covering both Gram-positive and Gram-negative organisms, aerobes and anaerobes, including methicillin-resistant S aureus, are given.Fungal and tubercular infections of spine are treated accordingly.
6-8 weeks of parenteral antibiotic therapy is effective in most cases. Before parenteral antibiotics are discontinued, the ESR should have fallen to at least two thirds.
Immobilization and rest is achieved by bed rest and/or bracing. The goal of immobilization is to provide opportunity for the affected level to fuse in an anatomically aligned position. Bracing is usually continued for 6-12 weeks.
Indications for surgery include significant osseous involvement, neurologic deficits, septic course with clinical toxicity from an abscess not responding to antibiotics, failure of needle biopsy to obtain necessary cultures, and failure of intravenous antibiotics alone to eradicate the infection.
Infections of Spine In Children
Vertebral osteomyelitis affects males more than females and is more common in adults than children with peak ages between 45 and 65 years. S aureus is The most common organism reported and in drug abusers Pseudomonas aeruginosa infection is common.
Presentation in Children
The child generally presents with fever. In older children, abdominal pain may be a presenting symptom
There would be difficulty in walking, malaise, irritability, and sudden inability to stand or walk comfortably.
The average age of onset is 6 to 7 years.
The symptoms could be of long duration before presentation to hospital.
Trauma has been implicated as the cause but most common cause is a bacterial infection in other part of the body the body.
There are limited findings on physical examination.
There might be limitation of spinal flexion movement. The child may refuse to walk or may cry when walking
Neurological findings are very rare.
- Raised leucocytes
- Elveated erythrocyte sedimentation rate
- Narrowed involved disc space may be seen on plain xray but usually is normal
MRI is the best modality. A combination of bone scanning and 67Ga scanning also give earliest indication of possible infection[But are not totally diagnostic
Blood cultures of the sample withdrawn may be helpful identifying the organism.
The treatment consists of following modalities
- Bed rest and immobilization.
- Intravenous antibiotics until child can walk
- Oral antibiotics for an additional 3 weeks.
- Immobilization in cast or brace may be required for older children.
Surgical procedures are rarely required and persistent back pain rarely is a problem in children.
Following patients need vigrous evaluation by needle aspiration biopsy or culture and sensitivity
- Immunosuppressed individuals [Persons with poor immune response]
- Drug abusers
- Those with malignancies
- Poor response to conservative treatment
In children younger than 6 years old, discitis is mostly viral in origin and biposy and antibiotics may be deferred in these children.
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