PATHOGENESIS

 Vertebral osteomyelitis, also referred to as disk-space infection, septic diskitis, spondylodiskitis, or spinal osteomyelitis, is the most common manifestation of hematogenous bone infection in adults. This designation reflects a pathogenic process leading to involvement of the adjacent vertebrae and the corresponding intervertebral disk. In adults, the disk is avascular. Microorganisms invade via the segmental arterial circulation in adjacent endplates and then spread into the disk. Alternative routes of infection are retrograde seeding through the prevertebral venous plexus and direct inoculation during spinal surgery, epidural infiltration, or trauma. In the setting of implant surgery, microorganisms are inoculated either during the procedure or, if wound healing is impaired, in the early postoperative period.

EPIDEMIOLOGY

Vertebral osteomyelitis occurs more often in male than in female patients (ratio, 1.5:1). Between 1995 and 2008, the incidence rate increased from 2.2 to 5.8 cases/100,000 person-years. There is a clear age-dependent increase. Men age ≥70 years have a sixfold higher incidence rate than those <70 years. The observed increase in reported cases over time may reflect improvements in diagnosis resulting from the broad availability of MRI technology. In addition, the fraction of cases of vertebral osteomyelitis acquired in association with health care is increasing as a consequence of comorbidity and the rising number of invasive interventions.

MICROBIOLOGY

Vertebral osteomyelitis is typically classified as pyogenic or nonpyogenic. However, this distinction is arbitrary: in “nonpyogenic” cases (tuberculous, brucellar), macroscopic pus formation (caseous necrosis, abscess) is quite common. A more accurate scheme is to classify cases as acute or subacute/chronic. Whereas the microbiologic spectrum of acute cases is similar in different parts of the world, the spectrum of subacute/chronic cases varies according to the geographic region. The great majority of cases are monomicrobial in etiology. Of episodes of acute vertebral osteomyelitis, 40–50% are caused by Staphylococcus aureus, 12% by streptococci, and 20% by gram-negative bacilli—mainly Escherichia coli (9%) and Pseudomonas aeruginosa (6%). Subacute vertebral osteomyelitis is typically caused by Mycobacterium tuberculosis or Brucella species in regions where these microorganisms are endemic. Osteomyelitis due to viridans streptococci also has a subacute presentation; these infections most often occur as secondary foci in patients with endocarditis. In vertebral osteomyelitis due to Candida species, the diagnosis is often delayed by several weeks; this etiology should be suspected in IV drug users who do not use sterile paraphernalia. In implant-associated spinal osteomyelitis, coagulase-negative staphylococci and C. acnes—which, in the absence of an implant, are generally considered contaminants—typically cause low-grade (chronic) infections. As an exception, coagulase-negative staphylococci can cause native spinal osteomyelitis in cases of prolonged bacteremia (e.g., in patients with infected pacemaker electrodes or implanted vascular catheters that are not promptly removed).

CLINICAL MANIFESTATIONS

The signs and symptoms of vertebral osteomyelitis are nonspecific. Only about half of patients develop fever >38°C (>100.4°F), perhaps because patients frequently use analgesic drugs. Back pain is the leading initial symptom (>85% of cases). The location of the pain corresponds to the site of infection: the cervical spine in ~10% of cases, the thoracic spine in 30%, and the lumbar spine in 60%. One exception is involvement at the thoracic level in two-thirds of cases of tuberculous osteomyelitis and at the lumbar level in only one-third. This difference is due to direct mycobacterial spread via pleural or mediastinal lymph nodes in pulmonary tuberculosis.

Neurologic deficits, such as radiculopathy, weakness, or sensory loss, are observed in about one-third of cases of vertebral osteomyelitis. Neurologic signs and symptoms are caused mostly by spinal epidural abscess. This complication starts with severe localized back pain and progresses to radicular pain, reflex changes, sensory abnormalities, motor weakness, bowel and bladder dysfunction, and paralysis.

A primary focus should always be sought but is found in only half of cases. Overall, endocarditis is identified in ~10% of patients. In osteo myelitis caused by viridans streptococci, endocarditis is the source in about half of patients.

Implant-associated spinal osteomyelitis can present as either early- or late-onset infection. Early-onset infection is diagnosed within 30 days after implant placement. S. aureus is the most common pathogen. Wound healing impairment and fever are the leading findings. Late-onset infection is diagnosed beyond 30 days after surgery, with low-virulence organisms such as coagulase-negative staphylococci or C. acnes as typical infecting agents. Fever is rare. One-quarter of patients have a sinus tract. Because of the delayed course and the lack of classic signs of infection, rapid diagnosis requires a high degree of suspicion.

DIAGNOSIS

 Leukocytosis and neutrophilia have low levels of diagnostic sensitivity (only 65% and 40%, respectively). In contrast, an increased erythrocyte sedimentation rate or C-reactive protein (CRP) level has been reported in 98% and 100% of cases, respectively; thus, these tests are helpful in excluding vertebral osteomyelitis. The fraction of blood cultures that yield positive results depends heavily on whether the patient has been pretreated with antibiotics; across studies, the range is 30–78%. In view of this low rate of positive blood culture after antibiotic treatment, such therapy should be withheld until microbial growth is proven unless the patient has sepsis syndrome. In patients with negative blood cultures, CT-guided or open biopsy is needed. Whether a CT-guided biopsy with a negative result is repeated or followed by open biopsy depends on the experience of personnel at the specific center. Bone samples should be cultured for aerobic, anaerobic, and fungal agents, with a portion of the sample sent for histopathologic study. In cases with a subacute/chronic presentation, a suggestive history, or a granuloma detected during histopathologic analysis, mycobacteria and brucellae also should be sought. When blood and tissue cultures are negative despite suggestive histopathology, nonculture techniques (eubacterial or multiplex polymerase chain reaction analysis, metagenomics) of biopsy specimens or aspirated pus should be considered. These techniques allow detection of unusual pathogens such as Helicobacter spp. or Tropheryma whipplei.

Given that signs and symptoms of osteomyelitis are nonspecific, the clinical differential diagnosis of febrile back pain is broad, including pyelonephritis, pancreatitis, and viral syndromes. In addition, multiple noninfectious pathologies of the vertebral column, such as osteoporotic fracture, seronegative spondylitis (ankylosing spondylitis, psoriasis, reactive arthritis, enteropathic arthritis), and spinal stenosis must be considered.

Imaging procedures are the most important tools not only for the diagnosis of vertebral osteomyelitis but also for the detection of pyo genic complications and alternative conditions (e.g., bone metastases or osteoporotic fractures). Plain radiography is a reasonable first step in evaluating patients without neurologic symptoms and may reveal an alternative diagnosis. Because of its low sensitivity, plain radiography generally is not helpful in acute osteomyelitis, but it can be useful in subacute or chronic cases. The gold standard is MRI, which should be performed expeditiously in patients with neurologic impairment in order to rule out a herniated disk or to detect pyogenic complications in a timely manner (Fig. 1, left). Even if the pathologic findings on MRI suggest vertebral osteomyelitis, alternative diagnoses should be considered, especially when blood cultures are negative. The most common alternative diagnosis is erosive osteochondrosis. Septic bone necrosis, gouty spondylodiskitis, and erosive diskovertebral lesions (Andersson lesions) in ankylosing spondylitis may likewise mimic vertebral osteomyelitis. CT is less sensitive than MRI but may be helpful in guiding a percutaneous biopsy. Positron emission tomography (PET) with 18F-fluorodeoxyglucose, which has a high degree of diagnostic accuracy, is an alternative imaging procedure when MRI is contra indicated (Fig. 1, right). 18F-fluorodeoxyglucose PET should be considered for patients with implants and patients in whom several foci are suspected.

Fig1. Left: MRI from a 53-year-old man suffering from prosthetic aortic valve endocarditis (Aggregatibacter actinomycetemcomitans). In addition, he experienced lumbar pain for 7 weeks. MRI sagittal sequence shows on T1 fat-saturated post-gadolinium image enhancement in the intervertebral disk space (ventral arrow) and a small epidural abscess (dorsal arrow). Right: PET/CT from the same patient 4 weeks earlier. PET/CT fusion shows fluorodeoxyglucose uptake at L5 ventral (small arrow) and dorsal of S1 (large arrow: epidural abscess). (Figures courtesy of Damien Toia, MD, Kantonsspital Baselland; with permission.

اخر الاخبار

اخبار العتبة العباسية المقدسة

شعبة الخطابة تقيم مجلس عزاء بذكرى شهادة الإمام الحسن العسكري (عليه السلام)

قسم الشؤون الطبية يُنهي استعداداته لإحياء شهادة الإمام الحسن العسكري (عليه السلام) في سامراء

بالصور.. المؤمنون يتوافدون إلى سامراء لإحياء ذكرى شهادة الإمام الحسن العسكري (عليه السلام)

العتبة العباسية المقدسة تنشر لافتات العزاء بذكرى شهادة الإمام الحسن العسكري (عليه السلام)

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المزيد

مواضيع ذات صلة

Periprosthetic Joint Infection

Osteomyelitis in Long Bones

Human Hematopoietic Stem Cells

Embryonic Origin of Hematopoietic Stem Cells

نقي العظم (النخاع العظمي) Bone marrow

تكوين الدم Haematopoiesis

Gastrointestinal decontamination

تطبيقات البرايون ودوره المثير في مفهوم العقيدة المركزية

تصوير الأوعية التاجية

أدواء البريونات

Stages of Neutrophil Differentiation

Types of Bone