Spinal Disorders: Fundamentals of Diagnosis and Treatment Part 103 ppt

Classifcation of spinal infections Causative organism Spatial location pyogenic infections tuberculosis parasitic infections fungal infections vertebrae spondylitis intervertebral

a b

Figure 1 Pathomechanism of spinal infections

aThe richly vascularized vertebral bodies with their valveless venous plexus (Batson) predispose to infection in this

ana-tomic region.bHematogenous seeding from peripheral ulcers, genitourinary infection, or pulmonary infection can

result in an outbreak of the infection close to the vertebral endplates and affect the intervertebral disc.

Pathogenesis

The richly vascularized vertebral bodies predispose

to spinal infections

Spinal infections are assumed to start from the disc space in children, in whom

the intervertebral disc is still vascularized In contrast, the disease appears to

start from the vertebral endplates in adults However, this strict distinction has

recently been questioned by Ring et al [41], who consider it more a continuous

disease The blood supply to the vertebral bodies and intervertebral disc

remains a key issue in the predilection of spinal infections The most frequent

pathomechanism is a hematogenous spread of microorganisms via the blood

vessels, resulting from urogenital, pulmonary, or diabetic foot infections

(Fig 1 ) Batson [2] assumed that the valveless venous plexus and the slow

blood flow within predisposes to spinal infections of the vertebral body Wiley

and Trueta [50] have provided evidence from injection studies that the arterial

route is of significant relevance Today it is assumed that both mechanisms

play a role With the increased frequency of spinal interventions, direct

inocu-lation of microorganisms has become an additional relevant pathomechanism

[3, 4, 10]

Classification

Spinal infections can be classified according to the causative organism

Clas-sically, we differentiated between specific and so-called non-specific

infec-tions Today, it is more appropriate to differentiate tuberculosis from

pyo-genic (e.g., Staphylococcus, Streptococcus, E coli), fungal (e.g., Aspergillus,

Cryptococcus neoformans), parasitic (e.g., Echinococcus) and postoperative

infections

Table 1 Classifcation of spinal infections Causative organism Spatial location

) pyogenic infections ) tuberculosis ) parasitic infections ) fungal infections

) vertebrae (spondylitis) ) intervertebral disc (discitis) ) epidural abscess

) paravertebral abscess

A different approach is to classify the spinal infection according to the anatomic region within the spine, i.e., anterior spine, spinal canal, or posterior spine More reasonable is differentiation with regard to the involvement of specific compart-ments, i.e., vertebral body, intervertebral disc, epidural, intradural or paraverte-bral (e.g., psoas muscle, retropharyngeal) extension (Table 1)

Clinical Presentation History

Diagnosis of spinal infection

is often delayed

Clinical presentation

is dependent on virulence,

host immunocompetence

and duration

The key feature of the history is the delayed diagnosis ( Case Introduction) In an extensive literature review, Sapico and Montgomerie [43] found that only 20 % of patients had a symptom duration of less than 3 weeks, 20 % had complaints for 3 weeks to 3 months, and the remaining 50 % of individuals had symptoms for more than 3 months prior to diagnosis The clinical presentation is related to the virulence of the organism, immunocompetence of the host, and duration of the

infection In this setting, Louis Pasteur’s maxim, “The organism is nothing, the

environment is everything,” has to be kept in mind In general, the history of

patients with spinal infections is highly variable and non-specific

The cardinal symptoms are:

) slowly progressive, continuous, and localized back pain

) pain exacerbation during rest and at night

) back pain and gibbus (in spinal tuberculosis)

Additional but less frequent findings may be:

) muscle spasm (e.g., torticollis)

) weight loss

) “feeling sick”

) pain exacerbation with movement and weight bearing (as signs of instability)

) pain in the loin, groin, or buttocks (due to an abscess)

) symptoms of radiculopathy and myelopathy (late) Search for

predisposing factors

Although the source of infection remains unidentified in more than one-third of

cases [43], predisposing factors should be specifically sought:

) diabetes mellitus

) intravenous drug abuser

) immune deficiency states

) preexisting paraplegia

) dental granuloma

) soft tissue ulcers

) urinary tract infections

) previous septic conditions Cardinal symptoms in

children and adults are similar

In children, spinal infections most frequently occur in the first decade of life The mean age at presentation appears to be lower in children with discitis

compared to vertebral osteomyelitis (2.8 vs 7.5 years of age) [15] The

presenta-tion of similar spinal infecpresenta-tion in children can differ from that in adults, while

the cardinal symptoms remain very similar, i.e., slowly progressing symptoms

with a general aspect of appearing ill Frequent findings in children are [15, 16,

49]:

) refusal to walk

) back pain and abdominal pain

) “appearing ill”

) fever (in cases of vertebral osteomyelitis)

Physical Findings

Physical findings are non-specific

Although clinical examination is seldom helpful in making the diagnosis, the

most frequent findings are:

) local tenderness (less specific)

) positive psoas sign

) pain provocation by flexion, rotation, and percussion

) limping (in children)

Triad of Pott: gibbus, spinal abscess, paraparesis

A thorough neurological examination is mandatory to diagnose neural

com-pression syndromes, in particular to rule out early para/tetraparesis

The classic clinical presentation of spinal tuberculosis includes back pain and

a gibbus and in later stages symptoms caused by an epidural abscess and

devel-oping neurologic deficits [23] In Western industrialized countries, patients

today present with less specific symptoms and often have an underlying general

illness (e.g., HIV, diabetes) The prevailing symptoms in a study by Fam and

Rubenstein were back pain and weight loss [13]

Diagnostic Work-up

Key to diagnosis is

“consider it”

The most important aspect of diagnosing spinal infection is to include this

diag-nosis in the differential diagdiag-nosis The diagnostic work-up is apparently clear

when spinal infection is considered as a cause of the patient’s symptoms and

con-sists of laboratory investigations, imaging studies, and biopsy

Laboratory Investigations

BSR, CRP and WBC are frequently elevated

The most helpful laboratory investigations are:

) elevated blood sedimentation rate (BSR)

) C-reactive protein (CRP)

) white blood cell count (WBC)

Infection parameters are sensitive but not specific

These inflammation markers are sensitive but non-specific and are more helpful

in terms of the temporal course rather than as absolute (single) values The

parameters can reliably be used to monitor treatment response The white blood

cell count is only elevated in about half of the patients and depends on the

nutri-tional state of the patient The determination of antibody titers for putative

bac-teria is valuable in identifying certain causative organisms

In the presence of a septic state, blood cultures should be obtained, but the hit

rate is low It can be increased if more than one blood sample (three to five

recom-mended) is taken from different veins

In putative tuberculosis, the Mantoux or tuberculin skin test is helpful to

investigate present or past exposure to Mycobacterium tuberculosis Direct

evi-a b Figure 2 Radiographic findings in spinal infection

The classical radiographic signs of spinal infection consist ofaloss of vertebral endplate definition,bdecrease of disc height, gradual development of osteolysis, development of a paravertebral soft tissue mass, and reactive changes with sclerosis.

dence can seldom be obtained from examination of material aspirated from an abscess

Imaging Studies

Modern imaging modalities have substantially improved accuracy in diagnosing spinal infection However, standard radiographs are still very helpful because they allow an overview of the osseous destruction and resulting deformity

Standard Radiographs

Radiographic diagnosis is

hampered by a delay in the

appearance of alterations

The major drawback of standard radiography is the delay in the appearance of radiographic signs (Fig 2 ) The sequence of changes demonstrable on

radio-graphs is [48]:

) loss of vertebral endplate definition (at earliest 10 – 14 days after onset)

) reduction of disc height

) gradual development of endplate osteolysis

) development of a paravertebral soft tissue mass

) reactive changes with sclerosis and new bone formation (at earliest 4 – 6 weeks after onset)

) vertebral collapse (late) with spinal deformity (kyphosis/scoliosis)

Magnetic Resonance Imaging

MRI is the imaging study

of choice

Today MRI has become the imaging modality of choice in diagnosing spinal infection Recent comparisons with bone scans have demonstrated that MRI is as accurate and sensitive [48]

Characteristic findings ( Fig 3) suggestive of spinal infections are [11]:

) decreased vertebral endplate signal intensity on T1-weighted images (95 %)

a b c

Figure 3 MRI characteristics of spinal infections

aThe predominant features of spinal infections are decreased vertebral body signal intensity on T1-weighted images,

bloss of endplate definition and increased disc signal on T2-weighted images, increased vertebral body signal intensity

on T2-weighted images and increased signal intensity on T1-weighted fat-suppressed images after injection of

gado-pentetate.cNote the retrovertebral epidural spinal abscess (arrow).

) loss of endplate definition (95 %)

) increased disc signal on T2-weighted images (95 %)

) increased vertebral endplate signal intensity on T2-weighted images (56 %)

) contrast enhancement of the disc and vertebral body (94 %)

The increased signal intensity is more obvious on short tau inversion recovery

(STIR) or frequency-selective fat-suppressed T2-weighted spin echo sequence,

but with the depiction of less anatomical detail [11]

In appropriate cases, the diagnosis of spinal tuberculosis (Fig 4) can be made

by MRI with high diagnostic accuracy [46] Loke et al [28] have reported that the

most common site is the lumbar spine, often with involvement of more than one

Contrast enhancement

is helpful in differentiating spinal TB from other granulomatous infections

vertebra Contrast enhancement is helpful in differentiating spinal tuberculosis

from other granulomatous infections [46] Frequent findings [28] suggestive of

spinal tuberculosis are:

) paraspinal soft-tissue masses (73 %)

) vertebral destruction and collapse (73 %)

) epidural abscess (53 %)

) posterior element involvement (40 %)

) intraosseous abscess (20 %) with contrast enhancement

Computed Tomography

CT demonstrates bony destruction better than MRI

The predominance of computed tomography in diagnosing spinal infections has

been surpassed by MRI because of its spatial resolution, multiplanar capabilities

and tissue contrast However, CT still has a role with regard to the assessment of the

osseous destruction, which is important for the choice of treatment (i.e.,

non-oper-a b c d

Figure 4 Radiographic features of spinal tuberculosis

Spinal tuberculosis can be diagnosed with satisfactory accuracy using standard radiographs and MRI The key findings include paraspinal soft-tissue masses, vertebral destruction and collapse, epidural abscess, posterior element involve-ment, and intraosseous abscess.

ative vs surgical) and planning of the surgical approach and technique It is also invaluable in patients unsuitable for an MRI scan (e.g., because of a pacemaker)

Radionuclide Studies

Bone scan and FDG-PET

are helpful in making the diagnosis

Because of the comparable diagnostic accuracy of MRI, technetium-99m labeled methylene-diphosphonate (Tc-99m MDP) bone scintigraphy is today more infre-quently used in the diagnosis of spinal infections However, an indication for a bone scan is still the search for a focus lesion, e.g., dental granuloma and osteo-myelitis

Confusion may arise with regard to the differential diagnosis of a degenerative endplate abnormality and spinal infections Positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose (FDG) (Fig 5) has been used in sus-pected spinal infection [45] In a recent study, FDG-PET has been shown to be helpful in differentiating spinal infection from disc degeneration because the lat-ter condition generally does not show FDG uptake [47]

Biopsy

Biopsy is a “must”

prior to treatment

The isolation of the causative organism is of utmost importance and must be attempted in every case While a biopsy can be performed under image

intensi-fier control, CT guidance [7, 34, 39] is preferable because of the accurate spatial

resolution, which is important to document that the biopsy was actually taken from within the lesion This is particularly valid in areas that are difficult to access, such as the sacrum or sacroiliac joints and upper thoracic or cervical region [48]

Percutaneous needle biopsy provides a definitive diagnosis ranging from 57 %

to 92 % [7, 34, 39] and depends on previous antibiotic treatment

The most frequently found organisms are:

) Staphylococcus aureus (30 – 55 %)

) gram-negative organisms (e.g., E coli, Salmonella, Enterococcus, Proteus)

) Pseudomonas aeruginosa (in 65 % of drug abusers)

) Streptococcus viridans, epidermatitis

) Proprionibacterium acnes

a b

Figure 5 Radionuclide study of spinal infection

Positron emission tomography with FDG demonstrates uptake at the level of L4/5 (same patient as inFig 3), strongly

indicative of spinal infection.

Tuberculosis can mimic tumor

Differentiation of tuberculosis from tumor may sometimes be difficult and a

cul-ture takes considerable time In the clinical situation it is not possible to await the

results from the culture and the diagnosis has to rely on the imaging findings

Non-operative Treatment

Do not start treatment prior to isolation of the causative organism (if possible)

In the absence of a life-threatening condition, treatment of spinal infections

should not be started without vigorous attempts to isolate the causative

organ-ism It is mandatory to obtain the causative organism prior to antibiotic

treat-ment because of the substantially reduced likelihood of a secondary diagnosis

(Case Introduction) In the absence of a causative organism and progressing

infection despite (non-specific) antibiotic treatment, high-dose broad-spectrum

double or triple drug chemotherapy is often required However, subsequent

severe pharmacological side effects may limit the use of high-dose antibiotics

and may result in a life-threatening situation if the infection is not controlled

This holds true for conservative as well as surgical treatment

Table 2 General objectives of treatment

) eradicate the infection

) prevent recurrence

) relieve pain

) prevent or reverse a neurologic deficit ) restore spinal stability

) correct spinal deformity

Non-operative therapy

is still the gold standard for uncomplicated cases

The choice of treatment is related to the chances of achieving the general

objec-tives of treatment with the respective therapy (Table 2) While radical

debride-ment, internal fixation, and appropriate antibiotic treatment have become the

gold standard in the treatment of osteomyelitis of long bones, the mainstay for

Table 3 Favorable indications for non-operative treatment

) single disc space infection (discitis)

) known causative organism

) absence of gross bony destruction and instability

) mobile patients with only moderate pain ) absence of relevant neurologic deficit ) rapid normalization of inflammation parameters

the treatment of spinal infection is still non-operative (Table 3) However, the trend in the literature is to support more aggressive treatment of spinal infections even in situations where non-operative treatment can be successful This trend is because of a shorter hospitalization and recovery time

The mainstay of treatment

is chemotherapy

The mainstay for the treatment of bacterial and parasitic infection is still rest

and intravenous antibiotics for a minimum of 4 – 6 weeks, depending on the extent of the infection and organism (Case Study 1) As outlined above, specific chemotherapy is mandatory Depending on the resistance of the organism and the bone penetration of the respective antibiotic drug, administration by the oral route may be appropriate for the post-primary treatment We strongly recom-mend that the antibiotic treatment be discussed with an infection specialist to

Case Study 1

A 70-year-old woman presented with an infected great toe and was treated with antibiotics for 3 weeks after a biopsy

was taken The biopsy revealed Proteus mirabilis and Pseudomonas aeruginosa as the responsible germs Two months

later the patient developed severe neck pain, which became worse with movement There were no radicular symptoms

or neurologic deficits The radiographic evaluation of the cervical spine demonstrated blurred endplates and somewhat narrowed disc space (a) The MRI showed strong evidence of a spinal infection at the level of C3/4 (b,c) Note the contrast

enhancement from C2 to C5 (d) There was no epidural abscess or spinal cord compromise A CT-guided needle biopsy did not reveal a positive result, but allowed the exclusion of a tumor This case exemplifies the notion that detection of

a germ after previous antibiotic treatment is unlikely Bone scintigraphy provided further evidence of an infection (e) The patient was treated with double chemotherapy and a hard collar In the absence of a neurologic deficit, severe pain

or substantial deformity, non-operative treatment was successful The patient recovered completely from her symptoms within 2 months.

allow for the most specific (narrow) drug therapy with the least chances of

phar-macological side effects

According to Pertuiset et al [35], there appears to be a consensus that the

ini-tial antituberculous treatment should consist of a triple (isoniazid, rifampin, and

pyrazinamide) or quadruple chemotherapy (plus ethambutol) given for 2 – 3

months After this period, chemotherapy should be continued with isoniazid and

rifampin in the absence of resistance or side effects There is still debate on the

optimal duration of antituberculous chemotherapy required for complete

recov-ery While a minimum of 12 months is favored by the majority of experts, no

con-vincing evidence can be derived from the literature [35]

Early ambulation

is attempted

While bedrest may be indicated for the initial treatment, early mobilization of

the patient with an orthosis is recommended The need for cast immobilization,

including neck or thigh extension, has to be determined on an individual basis and

depends on the location of the infection, general condition, and age of the patient

CRP is helpful

in monitoring healing

of infection

It is imperative to monitor the treatment success by regular determination of

the inflammation parameters (i.e., SR, CRP, and WBC) Follow-up imaging

stud-ies should be done in the case of persistent symptoms and in the absence of

decreasing inflammation parameters In general, antibiotic treatment should be

continued for at least 4 – 6 weeks because of a high recurrence rate in pyogenic

spinal infections Antibiotic treatment should only be ceased after normalization

of the CRP

Indication for a change from non-operative to operative treatment is the

per-sistence of the infection despite adequate antibiotic treatment or in the presence

of pharmacological side effects (e.g., kidney or liver dysfunction) limiting the

further use of specific antibiotics in adequate dosage A recent study has

demon-strated a favorable outcome by surgical treatment in this situation [8]

Operative Treatment

General Principles

Although the majority of cases with spinal infections can be successfully treated

non-operatively, surgery may become necessary in about one-third of the

patients (Table 4):

Table 4 Indications for surgery

) disease progression despite adequate antibiotic treatment

) progressive spinal deformity and instability

) neurological compromise ) incapacitating pain

Increasing evidence is presented in the literature [32] that radical debridement

and bone grafting of specific (TB) spinal infections are superior to non-operative

treatment [30, 33] Less information is available from the literature with regard to

the treatment of pyogenic infections On the other hand, no evidence is presented

that the spinal infection responds differently to radical debridement and bone

grafting than to long bone osteomyelitis No reports indicate that this approach

is ill-advised in cases where conservative treatment does not result in rapid

reso-lution of the infection and recovery of the patient

Surgical Techniques

The surgical approach is largely dependent on the extent and location of the

infection, spinal destruction, neurologic deficits, health status, and comorbidity

of the patient (Fig 6)

a b

Figure 6 Surgical treatment of spinal infections

The key to the treatment of spinal infections is radical debridement of the infected spine.aOften spinal infections are associated with disc space collapse, instability, and kyphotic deformity In cases of thoracolumbar spondylodiscitis, an accepted standard for the treatment of spinal infection today is posterior instrumentation, followed by anterior radical debridement In a first step, the spine is exposed by a posterior approach Pedicle screws are inserted in the vertebrae adjacent to the infection If a kyphotic deformity is present, a lordic prebent rod is first inserted and connected to the dis-tal screws.bBy levering the rod into the distal screws, the deformity is corrected.cIn a second stage, the spine is approached anteriorly With curets and pituitary forceps, the infected area is debrided to the bleeding bone The inter-vertebral disc is resected as completely as possible.dThe anterior column is reconstructed with a tricortical iliac bone graft and additional circumferential cancellous bone.

Percutaneous Debridement and Drainage

In discitis with suspicion of abscess formation, percutaneous debridement and drainage is the preferred treatment [17, 18] It can be performed using local

anesthesia, sufficient material can be obtained for culture, and it allows for debridement and drainage of the infection