Adult Pyogenic Vertebral Osteomyelitis - Spine

Introduction
Vertebral osteomyelitis, also known as spondylodiskitis Epidemiology demographics usually seen in adults (median age for pyogenic osteomyelitis is 50 to 60 years) location 50-60% of cases occur in lumbar spine 30-40% in thoracic spine ~10% in cervical spine risk factors include IV drug abuse diabetes recent systemic infection (UTI, pneumonia) obesity malignancy immunodeficiency or immunosuppressive medications malnutrition (serum albumin < 3 g/dL indicative of malnutrition) trauma smoking Pathophysiology pathogens staph aureus most common (50-65%) staph epidermidis is second most common cause gram negative infections increasing over last decade and often associated with gram negative infections of the GU and respiratory tract pseudomonas seen in patients with IV drug use salmonella seen in patients with sickle cell disease inoculation hematogenous seeding generally agreed that inoculation likely occurs through hematogenous seeding (arterial or venous) of the endplates and intervertebral discs endplates contain area of low-flow vascular anastomosis that may provide an environment suited for inoculation involvement of one endplate leads to direct extension into intervertebral discs, followed by direct extension into the second endplate direct inoculation can occur after penetrating trauma, open fractures, and following surgical procedure contiguous spread from local infection most commonly associated with retropharyngeal and retroperitoneal abscesses neurologic involvement neurologic deficits present in 10-20% results from direct infectious involvement of neural elements compression from an epidural abscess compression from instability of the spine Associated conditions epidural abscess defined as a collection of pus or inflammatory granulation tissue between dura mater and surrounding adipose tissue epidemiology usually associated with vertebral osteomyelitis present in ~18% of patients with spondylodiskitis 50% of patients with an epidural abscess will have neurologic symptoms
Presentation
History history of UTI, pneumonia, skin infection, of organ transplant are common Symptoms fever is only present in 1/3 of patients pain pain is often severe and insidious in onset pain is usually worse with activity and unrelenting in nature pain that awakens patients at night should raise concern for malignancy and infection neurologic symptoms present in 10-20% radiculopathy myelopathy Physical exam perform careful neurological exam
Imaging
Radiographs findings are usually delayed by weeks findings include paraspinous soft tissue swelling (loss of psoas shadow) seen if first few days disc space narrowing and disc destruction seen at 7-10 days remember disc destruction is atypical of neoplasm endplate erosion or sclerosis seen at 10-21 days local osteopenia CT useful to show bony abnormalities, abscess formation, and extent of bony involvement MRI MRI with gadolinium contrast indications gold standard for diagnosis and treatment sensitivity and specificity most sensitive (96%) and specific (93%) imaging modality for diagnosis of spinal osteomyelitis also most specific imaging modality to differentiate from tumor findings include paraspinal and epidural inflammation disc and endplate enhancement with gadolinium T2-weighted hyperintensity of the disk and endplate rim enhancing Bone scan Technetium Tc99m bone scans indications patients who can not obtain an MRI sensitivity and specificity 90% sensitive but lack specificity combined Technetium Tc99m and gallium 67 scan is both more specific and more sensitive than Technetium Tc99m alone indium 111 labeled scan not recommended due to poor sensitivity (17%)
Studies
Laboratory WBC elevated only in ~ 50% not a sensitive indicator for early infection ESR elevated in 90% of cases can be monitored serially to track success of treatment, however is considered less reliable than CRP CRP elevated in 90% of cases can be monitored serially to track success of treatment and is considered more reliable than ESR Blood cultures identification of organism is mandatory for treatment least invasive method to determine a diagnosis sensitivity & specificity ~33% (reports show 25%-66%) of patients with spondylodiskitis have positive blood cultures when positive 85% are accurate for isolating the correct organism blood culture yield is improved by withholding antibiotic and obtaining cultures when patient is febrile CT guided biopsy indications in patients who do not have indications for immediate open surgery and blood cultures are negative sensitivity & specificity can provide diagnosis in 68-86% of patients technique can be guided by fluoroscopy or by CT scan cultures should be sent for aerobic anaerobic fungal acid-fast cultures Open biopsy indications when tissue/organism diagnosis can not be made with noninvasive techniques technique anterior, costotransversectomy, or transpedicular approach used
Differential
Spinal Tumors MRI is the most specific imaging modality to differentiate from tumor features that weigh towards an infection include disc space involvement end-plate erosion significant inflammation Types of Spinal Osteomyelitis Bacterial Viral Tuberculosis Fungal
Treatment
Nonoperative bracing and long term antibiotic (6-12 weeks) indications most cases bracing helps improve pain and prevent deformity rigid cervicothoracic orthosis or halo required for cervical osteomyelitis antibiotics indications once organism has been identified via blood culture or biopsy if patient is septic or critically ill then start broad spectrum antibiotics immediately which include vancomycin for pencicillin-resistant and gram-positive bacteria third-generation cephalosporin for gram-negative coverage technique once organism has been identified usually treated with IV culture directed antibiotics until signs of improvement (~ 4-6 weeks) and then converted to PO antibiotics resistant strains new antibiotic-resistant strains of microorganisms are becoming more common and failure to diagnose can have negative consequences organisms include MRSA (methicillin-resistant Staph aureus) VRSA (vancomycin resistant Staph aureus) VRE (vancomycin resistant enterococcus) treatment newer generation antibiotics for antibiotic resistant organisms include linezolid and daptomycin outcomes successful in 80% Operative neurologic decompression, surgical debridement, and spinal stabilization indications refractory cases neurologic deficits progressive deformity & gross spinal instability technique dictated by characteristics of pathology anterior debridement and strut grafting, +/- posterior instrumentation considered to be gold standard posterior debridement and decompression alone usually ineffective for debridement may be indicated in some cases
Techniques
Anterior debridement and strut grafting, +/- posterior instrumentation goals identify organism eliminate infection prevent or improve neurologic deficits maintain spinal stability techniques strut graft selection autogenous tricortical iliac crest, rib, or fibula strut grafts have proven safe and effective in presence of acute infection allograft being used with good results, but autogenous sources theoretically have better incorporation a recent study showed improved deformity correction with titanium mesh cages filled with autograft (followed by posterior instrumentation) instrumentation spinal instrumentation in presence of active infection is controversial some advocate I&D followed by staged instrumentation some advocate a single procedure with bone graft and instrumentation in the presence of an active infection titanium is preferred over stainless steel posterior instrumentation posterior instrumentation indicated when severe kyphotic deformity or a multilevel anterior construct required posterior instrumentation can be performed at same time or as a staged procedure