Pyogenic Vertebral Osteomyelitis in the Thoracic Spine

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Pyogenic Vertebral Osteomyelitis in the Thoracic Spine
 


 

Pyogenic vertebral osteomyelitis in the thoracic spine is not rare, and is associated with a significant morbidity and mortality. Infection of the thoracic spine mostly results from hematogenous spread of bacteria from urinary tract and soft tissues. Early diagnosis of thoracic vertebral osteomyelitis remains a clinical challenge due to considerable variation of presentation and negative findings on plain radiographs. Delay in diagnosing vertebral osteomyelitis is not uncommon.
Incidence and Epidemiology
Pyogenic osteomyelitis is commonly seen in the lumbar and thoracic spine. The incidence of the thoracic pyogenic osteomyelitis reported from several studies ranges from 40% to 50% of all cases of spinal osteomyelitis. Pyegenic osteomyelitis in the thoracic spine may occur at any age group, but more than 50% of patients with thoracic osteomyelitis are seen in the age above 50 years old. Any condition that causes a bacteria may predispose a patient to thoracic osteomyelitis. The urinary tract and genitourinary procedures are the most common sources of infection, followed by soft tissue and respiratory infections. Immunocompromised patients and those with diabetes have a high incidence of vertebral infection. The patients with advanced age, diabetes or rheumatoid arthritis are associated with an increased risk of neurologic deficit. Staphylococcus aureus is the most common causative organism, whereas gram-negative organisms including Escherichia, Pseudomonas, and Proteus species are commonly responsible for genitourinary infections.
Pathophysiology
The metaphyseal region of the vertebral body is rich of end-arteriole network, which is supplied by the intercostal arteries in the thoracic spine. Once septic emboli lodge in the metaphyseal region, infection develops. The infection can spread into the adjacent disks, paravertebral or epidural spaces, and cause damage of the disks and formation of paraspinal, retromediastinal, or epidural abscess.
Spinal cord compromise can result from direct compression of epidural abscess, granulation tissue, or destroyed disk fragments, and caused by collapsed vertebral body. Ischemia may aggravate spinal cord damage as a result of septic thrombosis of the anterior spinal artery.
Clinical Features
The clinical presentation of vertebral osteomyelitis in the thoracic spine varies, depending on host resistance and organism virulence, and delayed diagnosis is common.
Back pain is the most common feature, which may be local or radicular in nature. Back pain may be aggravated with coughing, sneezing if epidural space is involved. Back pain may be the only symptom in the patients with subacute and chronic infections. Patients with acute infections may present with fever. The duration of symptoms from onset to the time of diagnosis varies from few days to 6 months because the symptoms of subacute and chronic infections are insidious.
Sensory and gait changes as well as weakness of the lower extremities may be present in patients with spinal cord compromise.
Physical Examination
Inspection of the back may reveal erythema over the area, and local tenderness may be palpated. The range of motion of the thoracic spine may be decreased due to paraspinal muscle spasm. Neurological deficits including decreased motor power and sensation of the lower extremities may be detected in the patients with spinal cord compression.
Laboratory Features
Laboratory studies are not specific, but helpful. The erythrocyte sedimentation rate (ESR) and c-reactive protein (CRP) level are valuable in diagnosis of pyogenic vertebral osteomyelitis. The ESR and CRP levels are elevated in most patients with spinal infections. The white blood cell (WBC) count can be elevated or normal. Blood cultures may be positive in 25% of patients. Urine should be checked for infection.
Radiographic Features
Plain radiographs may reveal bony destruction of the vertebral body, disk space narrowing, and end-plate erosion after several weeks of onset. A widened paravertebral or mediastinal shadow suggests the extension of infections.
Bone scan is sensitive in most of infectious lesions, but not specific.
Computed tomography (CT) scans best show bony destruction. Myelography followed by CT scans can further delineate the area and degrees of spinal cord compression from infectious processes, however, the risk of spreading infection should be considered.
Magnetic resonance imaging (MRI) has become the main modality in evaluation of vertebral osteomyelitis, and provides 94% of accuracy in diagnosis of spinal infections. An early stage of vertebral osteomyelitis can be detected by MRI. The infected vertebral bodies and disks usually show a decreased signal intensity on T1-weighted sequences, and an increased intensity on T2-weighted MRI. MRI can differentiate infection from tumors. Soft tissues and the epidural space can also be visualized by MRI.
Diagnostic Criteria and Differential Diagnosis
Thoracic vertebral osteomyelitis should be suspected in patients with back pain. A diagnosis of thoracic spine infection could be established through laboratory and appropriate imaging studies. However, the definite diagnosis of thoracic vertebral osteomyelitis can be made only through a positive blood cultures or tissue cultures obtained from close or open biopsy. CT-quided biopsy is currently the standard technique. Thoracic metastatic disease should be ruled out.
Treatment
Antimicrobial therapy is the mainstay of the treatment of pyogenic vertebral osteomyelitis. The selection of antibiotics depends on the results of blood or tissue cultures. Intravenous antibiotics are usually used for 4 to 6 weeks, and followed by 3 to 6 months of oral antibiotics. Immobilization of the thoracic spine using orthosis is necessary to relief back pain and prevent deformity.
Surgical intervention is indicated in patients with a epidural abscess, spinal cord compress, or significant instability secondary to pathological fractures or when conservation management is failed. Vertebral osteomyelitis and abscess in the thoracic spine are most approached through a transthoracic route. A costotransverse or lateral extracavitary approach may be considered, but its visibility and debridement may be limited. Debridement of all involved tissues should be aggressive until healthy bleeding bone is encountered. Autogenous iliac bone graft is recommended for reconstruction of the thoracic spine following complete spinal cord decompression and debridement. Stabilization of the spine with hardwares is controversial.