Imaging of musculoskeletal infections

Nuclear medicine and the failed joint replacement: Past, present, and future

Soon after the introduction of the modern prosthetic joint, it was recognized that radionuclide imaging provides useful information about these devices. The bone scan was used extensively to identify causes of prosthetic joint failure. It became apparent, however, that although sensitive, regardless of how the images were analyzed or how it was performed, the test was not specific and could not distinguish among the causes of prosthetic failure. Advances in anatomic imaging, notably cross sectional modalities, have facilitated the diagnosis of many, if not most, causes of prosthetic failure, with the important exception of infection. This has led to a shift in the diagnostic paradigm, in which nuclear medicine investigations increasingly have focused on diagnosing infection. The recognition that bone scintigraphy could not reliably diagnose infection led to the development of combined studies, first bone/gallium and subsequently leukocyte/bone and leukocyte/marrow imaging. Labeled leukocyte imaging, combined with bone marrow imaging is the most accurate (about 90%) imaging test for diagnosing joint arthroplasty infection. Its value not withstanding, there are significant disadvantages to this test. In-vivo techniques for labeling leukocytes, using antigranulocyte antibodies have been explored, but have their own limitations and the results have been inconsistent. Fluorodeoxyglucose (FDG)-positron emission tomography (FDG-PET) has been extensively investigated for more than a decade but its role in diagnosing the infected prosthesis has yet to be established. Antimicrobial peptides bind to bacterial cell membranes and are infection specific. Data suggest that these agents may be useful for diagnosing prosthetic joint infection, but large scale studies have yet to be undertaken. Although for many years nuclear medicine has focused on diagnosing prosthetic joint infection, the advent of hybrid imaging with single-photon emission computed tomography(SPECT)/electronic computer X-ray tomography technique (CT) and the availability of fluorine-18 fluoride PET suggests that the diagnostic paradigm may be shifting again. By providing the anatomic information lacking in conventional radionuclide studies, there is renewed interest in bone scintigraphy, performed as a SPECT/CT procedure, for detecting joint instability, mechanical loosening and component malpositioning. Fluoride-PET may provide new insights into periprosthetic bone metabolism. The objective of this manuscript is to provide a comprehensive review of the evolution of nuclear medicine imaging of joint replacements.

Pyogenic and non-pyogenic spinal infections: emphasis on diffusion-weighted imaging for the detection of abscesses and pus collections

The incidence of spinal infections has increased in the past two decades, owing to the increasing number of elderly patients, immunocompromised conditions, spinal surgery and instrumentation, vascular access and intravenous drug use. Conventional MRI is the gold standard for diagnostic imaging; however, there are still a significant number of misdiagnosed cases. Diffusion-weighted imaging (DWI) with a b-value of 1000 and apparent diffusion coefficient (ADC) maps provide early and accurate detection of abscess and pus collection. Pyogenic infections are classified into four types of extension based on MRI and DWI findings: (1) epidural/paraspinal abscess with spondylodiscitis, (2) epidural/paraspinal abscess with facet joint infection, (3) epidural/paraspinal abscess without concomitant spondylodiscitis or facet joint infection and (4) intradural abscess (subdural abscess, purulent meningitis and spinal cord abscess). DWI easily detects abscesses and demonstrates the extension, multiplicity and remote disseminated infection. DWI is often a key image in the differential diagnosis. Important differential diagnoses include epidural, subdural or subarachnoid haemorrhage, cerebrospinal fluid leak, disc herniation, synovial cyst, granulation tissue, intra- or extradural tumour and post-surgical fluid collections. DWI and the ADC values are affected by susceptibility artefacts, incomplete fat suppression and volume-averaging artefacts. Recognition of artefacts is essential when interpreting DWI of spinal and paraspinal infections. DWI is not only useful for the diagnosis but also for the treatment planning of pyogenic and non-pyogenic spinal infections.

The expanding horizon of prosthetic joint infections

Prosthetic joint infection (PJI) is a serious and potentially devastating complication of arthroplasty. Prior arthroplasty, immunosuppression, severe comorbid conditions, and prolonged surgical duration are important risk factors for PJI. More than half of the cases of PJI are caused by Staphylococcus aureus and coagulase-negative staphylococci. The biofilm plays a central role in its pathogenesis. The diagnosis of PJI requires the presence of purulence, sinus tract, evidence of inflammation on histopathology, or positive microbiologic cultures. The use of diagnostic imaging techniques is generally limited but may be helpful in selected cases. The most effective way to prevent PJI is to optimize the health of patients, using antibiotic prophylaxis in a proper and timely fashion. Management of PJI frequently requires removal of all hardware and administration of intravenous antibiotics. This review summarizes and analyzes the results of previous reports of PJI and assesses the prevention and management of this important entity.

Is switching to an oral antibiotic regimen safe after 2 weeks of intravenous treatment for primary bacterial vertebral osteomyelitis?

Background

Vertebral osteomyelitis (VO) may lead to disabling neurologic complications. Little evidence exists on optimal antibiotic management.

Methods

All patients with primary, non-implant VO, admitted from 2000–2010 were retrospectively analyzed. Patients with endocarditis, immunodeficiency, vertebral implants and surgical site infection following spine surgery were excluded. Persistence of clinical or laboratory signs of inflammation at 1 year were defined as treatment failure. Logistic regression was used to estimate the odds ratios (OR) of switch to an oral regimen after 2 weeks.

Results

Median antibiotic treatment was 8.1 weeks in 61 identified patients. Switch to oral antibiotics was performed in 72% of patients after a median intravenous therapy of 2.7 weeks. Switch to oral therapy was already performed after two weeks in 34% of the patients. A lower CRP at 2 weeks was the only independent predictor for switch to oral therapy (OR 0.7, 95% confidence interval 0.5-0.9, p = 0.041, per 10 mg/l increase). Staphylococcus aureus was the most frequently isolated microorganism (21%). Indications for surgery, other than biopsy, included debridement with drainage of epidural or paravertebral abscess (26 patients; 42%), and CT - guided drainage (3 patients).

During the follow-up, no recurrences were observed but 2 patients died of other reasons than VO, i.e. the 1 year intention to treat success rate was 97%.

Conclusions

Cure rates for non-implant VO were very high with partly short intravenous and overall antibiotic therapy. Switching to an oral antibiotic regimen after two weeks intravenous treatment may be safe, provided that CRP has decreased and epidural or paravertebral abscesses of significant size have been drained.

Imaging of diabetic foot infections

Complications from diabetic foot infections are a leading cause of nontraumatic lower-extremity amputations. Nearly 85% of these amputations result from an infected foot ulcer. Osteomyelitis is present in approximately 20% of diabetic foot infections. It is imperative that clinicians make quick and successful diagnoses of diabetic foot osteomyelitis (DFO) because a delay in treatment may lead to worsening outcomes. Imaging studies, such as plain films, bone scans, musculoskeletal ultrasound, computerized tomography scans, magnetic resonance imaging, and positron emission tomography scans, aid in the diagnosis. However, there are several mimickers of DFO, which present problems to making a correct diagnosis.

Sclerotic lesions of the spine: MRI assessment

Sclerotic (T2 dark) lesions of the spine are infrequent and, as a result, these are often missed or misdiagnosed. Plain films may not be always available during magnetic resonance imaging (MRI) readout. Knowledge of such lesions and their imaging appearances on MRI evaluation is essential for a reader. Additionally, a systematic approach is important to accurately diagnose these lesions. In this article we discuss the various causes of spinal sclerotic lesions, describe their MRI characteristics with relevant case examples, and outline a systematic approach to their evaluation.

Central Nervous System Infections

Central nervous system (CNS) infections—i.e., infections involving the brain (cerebrum and cerebellum), spinal cord, optic nerves, and their covering membranes—are medical emergencies that are associated with substantial morbidity, mortality, or long-term sequelae that may have catastrophic implications for the quality of life of affected individuals. Acute CNS infections that warrant neurointensive care (ICU) admission fall broadly into three categories—meningitis, encephalitis, and abscesses—and generally result from blood-borne spread of the respective microorganisms. Other causes of CNS infections include head trauma resulting in fractures at the base of the skull or the cribriform plate that can lead to an opening between the CNS and the sinuses, mastoid, the middle ear, or the nasopharynx. Extrinsic contamination of the CNS can occur intraoperatively during neurosurgical procedures. Also, implanted medical devices or adjunct hardware (e.g., shunts, ventriculostomies, or external drainage tubes) and congenital malformations (e.g., spina bifida or sinus tracts) can become colonized and serve as sources or foci of infection. Viruses, such as rabies, herpes simplex virus, or polioviruses, can spread to the CNS via intraneural pathways resulting in encephalitis. If infection occurs at sites (e.g., middle ear or mastoid) contiguous with the CNS, infection may spread directly into the CNS causing brain abscesses; alternatively, the organism may reach the CNS indirectly via venous drainage or the sheaths of cranial and spinal nerves. Abscesses also may become localized in the subdural or epidural spaces. Meningitis results if bacteria spread directly from an abscess to the subarachnoid space. CNS abscesses may be a result of pyogenic meningitis or from septic emboli associated with endocarditis, lung abscess, or other serious purulent infections. Breaches of the blood–brain barrier (BBB) can result in CNS infections. Causes of such breaches include damage (e.g., microhemorrhage or necrosis of surrounding tissue) to the BBB; mechanical obstruction of microvessels by parasitized red blood cells, leukocytes, or platelets; overproduction of cytokines that degrade tight junction proteins; or microbe-specific interactions with the BBB that facilitate transcellular passage of the microorganism. The microorganisms that cause CNS infections include a wide range of bacteria, mycobacteria, yeasts, fungi, viruses, spirochaetes (e.g., neurosyphilis), and parasites (e.g., cerebral malaria and strongyloidiasis). The clinical picture of the various infections can be nonspecific or characterized by distinct, recognizable clinical syndromes. At some juncture, individuals with severe acute CNS infections require critical care management that warrants neuro-ICU admission. The implications for CNS infections are serious and complex and include the increased human and material resources necessary to manage very sick patients, the difficulties in triaging patients with vague or mild symptoms, and ascertaining the precise cause and degree of CNS involvement at the time of admission to the neuro-ICU. This chapter addresses a wide range of severe CNS infections that are better managed in the neuro-ICU. Topics covered include the medical epidemiology of the respective CNS infection; discussions of the relevant neuroanatomy and blood supply (essential for understanding the pathogenesis of CNS infections) and pathophysiology; symptoms and signs; diagnostic procedures, including essential neuroimaging studies; therapeutic options, including empirical therapy where indicated; and the perennial issue of the utility and effectiveness of steroid therapy for certain CNS infections. Finally, therapeutic options and alternatives are discussed, including the choices of antimicrobial agents best able to cross the BBB, supportive therapy, and prognosis.

Diagnosis and management of prosthetic joint infection

PURPOSE OF REVIEW

Prosthetic joint infection remains a devastating complication of arthroplasty associated with significant patient morbidity. The demand for arthroplasty is rapidly growing with a corresponding increase in the number of infections involving the prosthesis. The diagnosis and treatment of prosthetic joint infections presents a significant challenge to orthopaedic and infectious diseases clinicians.

RECENT FINDINGS

The underlying pathogenesis of prosthetic joint infections is due to the ability of the microorganisms to form a biofilm. The biofilm provides protection against host immune responses and antimicrobial therapy. In addition, it impedes standard laboratory diagnostic techniques. This review will examine new investigations to improve the diagnostic yield and rapidity of diagnosis of infections, including the use of sonication to disrupt the biofilm, new molecular tests to improve the detection of infecting microorganisms and new imaging techniques such as (18)F-fluoro-deoxyglucose PET.

SUMMARY

The successful treatment of prosthetic joint infections is dependent on eliminating the biofilm dwelling microorganisms whilst maintaining patient mobility and quality of life. This review will examine current understanding of management approaches for these infections, with a particular focus on antimicrobial therapy with activity against the biofilm, such as rifampicin and fluoroquinolones.

Spondylodiscitis after Cervical Nucleoplasty without Any Abnormal Laboratory Findings

Infective spondylodiscitis is a rare complication that can occur after interventional spinal procedures, of which symptoms are usually back pain and fever. Early diagnosis of infective spondylodiscitis is critical to start antibiotics and to improve prognosis. Laboratory examinations including complet blood cell count (CBC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) are conventional tools for the early detection of infectious spondylitis. However, we experienced infective spondylodiscitis after cervical nucleoplasty which did not display any laboratory abnormalities, but was diagnosed through an MRI. A patient with cervical disc herniation received nucleoplasty at C5/6 and C6/7. One month later, the patient complained of aggravated pain. There were neither signs of chill nor fever, and the laboratory results appeared normal. However, the MRI findings were compatible with infectious spondylodiscitis at the nucleoplasty site. In conclusion, infectious spondylodiscitis can develop after cervical nucleoplasty without any laboratory abnormalities. Therefore, an MRI should be taken when there is a clinical suspicion for infection in order to not miss complications after interventional procedures, even if the laboratory findings are normal.

Salmonella Spinal Infection

We present an unusual case of nontyphoidal Salmonella causing an epidural abscess and vertebral osteomyelitis in a severely immunocompromised patient with AIDS as well as a review of the literature. Salmonella vertebral osteomyelitis is exceptionally rare, and this is the first case report in a patient with AIDS.

Magnetic resonance imaging of musculoskeletal infections: systematic diagnostic assessment and key points

Prompt diagnosis and treatment are essential in preventing the complications of musculoskeletal infection. In this context, imaging is often used to confirm clinically suspected diagnoses, define the extent of infection, and ensure appropriate management. Because of its superior soft-tissue contrast resolution, magnetic resonance imaging (MRI) is the modality of choice for evaluating musculoskeletal infections. This article describes the MRI features along the full spectrum of musculoskeletal infections and provides several illustrative case examples.

The Clinical Usefulness of (99m)Tc HMPAO Leukocyte/(99m)Tc Phytate Bone Marrow Scintigraphy for Diagnosis of Prosthetic Knee Infection: A Preliminary Study

PURPOSE

The preferred radionuclide imaging procedure for diagnosing prosthetic joint infection is combined radiolabeled leukocyte/(99m)Tc sulfur colloid bone marrow scintigraphy, which has an accuracy of over 90 %. Unfortunately, sulfur colloid is no longer available in South Korea. In this study, we evaluated the usefulness of (99m)Tc phytate, a substitute for (99m)Tc sulfur colloid, when combined with radiolabeled leukocyte scintigraphy in suspected prosthetic knee infections.

METHODS

Eleven patients (nine women, two men; mean age 72 ± 6 years) with painful knee prostheses and a suspicion of infection underwent both (99m)Tc HMPAO leukocyte scintigraphy (LS) and (99m)Tc phytate bone marrow scintigraphy (BMS). The combined images were interpreted as positive for infection when radioactivity in the LS at the site of clinical interest clearly exceeded that of the BMS (discordant); they were interpreted as negative when the increased activity in the LS was consistent with an increased activity in the BMS (concordant). The final diagnosis was made with microbiological or intraoperative findings and a clinical follow-up of at least 12 months.

RESULTS

Five of eleven patients were diagnosed as having an infected prosthesis. The overall sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of the combined LS/BMS were 100 %, 83 %, 83 %, 100 % and 91 %, respectively.

CONCLUSION

We find that combined (99m)Tc HMPAO LS/(99m)Tc phytate BMS shows comparable diagnostic performance to other studies utilizing sulfur colloid. Combined (99m)Tc HMPAO LS/(99m)Tc phytate BMS is therefore expected to be an acceptable alternative to combined radiolabeled LS/(99m)Tc sulfur colloid BMS for diagnosing prosthetic knee infections.

Spondylodiscitis: standards of current treatment

BACKGROUND

Spinal infections are an important clinical problem that often require aggressive medical therapy, and sometimes even surgery. Known risk factors are advanced age, diabetes mellitus, rheumatoid arthritis, immunosuppression, alcoholism, long-term steroid use, concomitant infections, poly-trauma, malignant tumor, and previous surgery or invasive procedures (discography, chemonucleolysis, and surgical procedures involving or adjacent to the intervertebral disc space). The most common level of involvement is at the lumbar spine, followed by the thoracic, cervical and sacral levels: lesions at the thoracic spine tend to lead more frequently to neurological symptoms.

OBJECTIVE

The aim of the current paper is to describe current evidence-based standards of therapy in the management of SD by emphasizing pharmacological therapy and principles and indications for bracing and surgery.

METHODS

A PubMed and Google Scholar search using various forms and combinations of the key words: spondylodiscitis, spine, infection, therapy, surgery, radiology, treatment. Reference citations from publications identified in the literature search were reviewed. Publications highlighted in this article were extracted based on relevancy to established, putative, and emerging diagnostic and therapeutic standards, either conservative (antibiotic therapy and bracing) or surgical.

FINDINGS

To date, conservative therapy, based on targeted antibiotic therapy plus bracing, represents the mainstay in the management of SD. Proper diagnosis and tailored therapy can improve clinical results and decrease the chance of failure. Surgery should be an option only for patients with complications of this disease, namely deformity, neural compression and neurological compromise. Current standards in the setting of SD are continuously evolving, as can be seen in the recent advances in the field of radiological diagnostics, and the use of growth factors and cell-therapy strategies to promote infection eradication and bone healing after surgery.

Metastatic infectious disease and clinical outcome in Staphylococcus aureus and Streptococcus species bacteremia

Early detection of metastatic infection in patients with Gram-positive bacteremia is important as morbidity and mortality are higher in the presence of these foci, probably due to incomplete eradication of clinically silent foci during initial treatment. We performed a prospective study in 115 patients with Staphylococcus aureus or Streptococcus species bacteremia with at least 1 risk factor for the development of metastatic foci, such as community acquisition, treatment delay, persistently positive blood cultures for >48 hours, and persistent fever >72 hours after initiation of treatment. An intensive search for metastatic infectious foci was performed including ¹⁸F-fluorodeoxyglucose-positron emission tomography in combination with low-dose computed tomography scanning for optimizing anatomical correlation (FDG-PET/CT) and echocardiography in the first 2 weeks of admission. Metastatic infectious foci were detected in 84 of 115 (73%) patients. Endocarditis (22 cases), endovascular infections (19 cases), pulmonary abscesses (16 cases), and spondylodiscitis (11 cases) were diagnosed most frequently. The incidence of metastatic infection was similar in patients with Streptococcus species and patients with S. aureus bacteremia. Signs and symptoms guiding the attending physician in the diagnostic workup were present in only a minority of cases (41%). An unknown portal of entry, treatment delay >48 hours, and the presence of foreign body material were significant risk factors for developing metastatic foci. Mean C-reactive protein levels on admission were significantly higher in patients with metastatic infectious foci (74 vs. 160 mg/L). FDG-PET/CT was the first technique to localize metastatic infectious foci in 35 of 115 (30%) patients. As only a minority of foci were accompanied by guiding signs or symptoms, the number of foci revealed by symptom-guided CT, ultrasound, and magnetic resonance imaging remained low. Mortality tended to be lower in patients without complicated infection compared to those with metastatic foci (16% vs. 25%, respectively). Five of 31 patients (16%) without proven metastatic foci died. In retrospect, 3 of these 5 patients likely had metastatic foci that could not be diagnosed while alive. In patients with Gram-positive bacteremia and a high risk of developing complicated infection, a structured protocol including echocardiography and FDG-PET/CT aimed at detecting metastatic infectious foci can contribute to improved outcome.

Prosthetic joint infections: radionuclide state-of-the-art imaging

Prosthetic joint replacement surgery is performed with increasing frequency. Overall the incidence of prosthetic joint infection (PJI) and subsequently prosthesis revision failure is estimated to be between 1 and 3%. Differentiating infection from aseptic mechanical loosening, which is the most common cause of prosthetic failure, is especially important because of different types of therapeutic management. Despite a thorough patient history, physical examination, multiple diagnostic tests and complex algorithms, differentiating PJI from aseptic loosening remains challenging. Among imaging modalities, radiographs are neither sensitive nor specific and cross-sectional imaging techniques, such as computed tomography and magnetic resonance imaging, are limited by hardware-induced artefacts. Radionuclide imaging reflects functional rather than anatomical changes and is not hampered by the presence of a metallic joint prosthesis. As a result scintigraphy is currently the modality of choice in the investigation of suspected PJI. Unfortunately, there is no true consensus about the gold standard technique since there are several drawbacks and limitations inherent to each modality. Bone scintigraphy (BS) is sensitive for identifying the failed joint replacement, but cannot differentiate between infection and aseptic loosening. Combined bone/gallium scintigraphy (BS/GS) offers modest improvement over BS alone for diagnosing PJI. However, due to a number of drawbacks, BS/GS has generally been superseded by other techniques but it still may have a role in neutropenic patients. Radiolabelled leucocyte scintigraphy remains the gold standard technique for diagnosing neutrophil-mediated processes. It seems to be that combined in vitro labelled leucocyte/bone marrow scintigraphy (LS/BMS), with an accuracy of about 90%, is currently the imaging modality of choice for diagnosing PJI. There are, however, significant limitations using in vitro labelled leucocytes and considerable effort has been devoted to developing alternative radiotracers, such as radiolabelled HIGs, liposomes, antigranulocyte antibodies and fragments, as well as more investigational tracers such as radiolabelled antibiotics, antimicrobial peptides, bacteriophages and thymidine kinase. On the other hand, positron emission tomography (PET) is still growing in the field of PJI imaging with radiotracers such as (18)F-fluorodeoxyglucose (FDG), (18)F-FDG white blood cells and (18)F-fluoride. But unfortunately this superb tomographic technique will only receive full acceptance when specific PET uptake patterns can be successfully developed. The emergence of hybrid modality imaging using integrated single photon emission computed tomography (SPECT) and PET with computed tomography (SPECT/CT and PET/CT) may also have a contributing role for more accurate assessment of joint replacement complications, especially combined with new radiotracers such as (68)Ga and (64)Cu. Finally, in searching for infection-specific tracers, currently there is no such diagnostic agent available.

The role of diagnostic imaging in the evaluation of suspected osteomyelitis in the foot: a critical review

The early diagnosis of osteomyelitis in the foot from its clinical presentation alone can be difficult particularly in cases when the early signs are subtle. Early diagnosis and subsequent early intervention are imperative to reduce the risk of chronic infection, associated early lytic changes to bone and potential long term structural complications caused by subsequent deformity and lost anatomy. Diagnostic imaging has a major role to play in the early assessment and diagnosis of bone infection, yet the choice of approach can be controversial. Several imaging modalities have been advocated, imaging of the infected foot is complex and no single test is ideal for every situation. The clinician needs to be aware of the strengths and weaknesses of each imaging modality so that the most appropriate test is selected for the individual case. Factors such as site of infection in the foot, the aggressive nature of the organism, the time since onset, previous associated surgery and co-morbidity may all play apart in the clinician's decision making process to determine the best approach in detecting the sometimes subtle changes which may be seen in some cases of osteomyelitis. This review considers the literature and highlights the advantages and disadvantages of the main imaging techniques used for the evaluation of the foot when osteomyelitis is suspected. An evidence based algorithm for the selection of appropriate imaging techniques is suggested to aid clinicians in there decision making process.

PET/CT imaging in infectious conditions

New aggressive pathogens are responsible for the increasing incidence and difficult management of infections. Modern epidemics such as diabetes are frequently complicated by severe infections with subsequent high morbidity. Diagnosis (essentially early detection of infection) and also management decision making pose clinical challenges. Many resources are invested in developing precise, noninvasive diagnostic tests and efficient therapies for infectious processes. Nuclear medicine procedures are part of the evaluation armamentarium of patients with suspected or confirmed infection. Their strength relies on the fact that they are noninvasive tests that provide both functional as well as metabolic information early in the course of disease. Their limitations relate to the need for specific radiotracers and the rather low resolution of images. These limitations have been largely overcome by the hybrid PET/CT and SPECT/CT technology. PET/CT, primarily using FDG, is redefining the diagnostic work up and is currently leading to changes in the management of patients with suspected or known infections. The main indications for FDG PET/CT in infection, as well as updated literature results, are presented in the following review.

Imaging of inflammation by PET, conventional scintigraphy, and other imaging techniques

Nuclear medicine imaging procedures play an important role in the assessment of inflammatory diseases. With the advent of 3-dimensional anatomic imaging, there has been a tendency to replace traditional planar scintigraphy by CT or MRI. Furthermore, scintigraphic techniques may have to be combined with other imaging modalities to achieve high sensitivity and specificity, and some may require time-consuming labeling procedures. On the other hand, new developments such as combined SPECT/CT increase the diagnostic power of scintigraphy. Also, the advent of PET had a considerable impact on the use of nuclear medicine imaging techniques. In this review, we aim to provide nuclear medicine specialists and clinicians with the relevant information on rational and efficient use of nuclear medicine imaging techniques in the assessment of patients with osteomyelitis, infected vascular prostheses, metastatic infectious disease, rheumatoid arthritis, vasculitis, inflammatory bowel disease, sarcoidosis, and fever of unknown origin.

Miliary tuberculosis and necrotizing tuberculous fasciitis--an unusual coexistence in a rheumatoid arthritis patient

We report a case of a 65-year-old Korean female patient with rheumatoid arthritis, who presented with extensive necrotizing fasciitis of the gluteus muscles, as an unusual initial manifestation of miliary tuberculosis. The patient had been previously treated with conventional disease-modifying antirheumatic drugs and low-dose steroids for 7 years. However, she recently developed fever, warmth and painful swelling in her right buttock. Magnetic resonance imaging indicated necrotizing fasciitis of the gluteus muscles and a fasciectomy specimen revealed a Mycobacterium tuberculosis infection. Two weeks after a fasciectomy, miliary tuberculosis of the lung was diagnosed by high resolution chest computed tomography. Soft tissue infection due to M. tuberculosis should be included as a differential diagnosis in the immunocompromised host. Clinicians should be alert to the possibility of miliary tuberculosis even in the absence of respiratory symptoms and normal chest radiograph.

Prediction of residual disease of spine infection using F-18 FDG PET/CT

STUDY DESIGN

Prospective study.

OBJECTIVE

To determine whether F-18 fluoro-deoxy-glucose positron emission tomography/computed tomography (F-18 FDG PET/CT) follow-up imaging after treatment in patients with spinal infection (SI) could provide useful prognostic information and determine the residual SI.

SUMMARY OF BACKGROUND DATA

There are seldom data on the capability of follow-up imaging methods to predict residual disease and treatment efficacy in patients with SI.

METHODS

Thirty patients with SI underwent F-18 FDG PET/CT at initial and during follow-up. From F-18 FDG PET/CT, quantitative indexes were obtained. The residual SI was determined by the presence of preoperative symptoms, hematological infection marker, and radiologic findings.

RESULTS

The SUVmax were significantly declined after treatment in both of residual (2.85 +/- 1.17 vs. 2.06 +/- 1.03; P < 0.0001) and nonresidual SI (4.31 +/- 2.07 vs. 1.44 +/- 0.46; P < 0.0001). The SUVmean were also decreased after treatment in both of residual (1.45 +/- 0.45 vs. 1.04 +/- 0.29; P = 0.0014) and nonresidual SI (2.09 +/- 1.03 vs. 0.81 +/- 0.25; P < 0.0001). By lesion-based analysis, when < or =43.01% of %deltaSUVmax was used as threshold value, the area under curve (AUC) was 0.879 (P = 0.0001). The sensitivity and specificity were 85.7% and 82.6%, respectively. When < or =44.12% of %deltaSUVmean was used as threshold value, AUC was 0.828 (P = 0.0001). The sensitivity and specificity were 85.7% and 68%, respectively. In patient-based analysis, when < or =46.14% of %deltaSUVmax was used as threshold value, AUC was 0.904 (P = 0.0001). The sensitivity and specificity were 100% and 76.9%, respectively. When < or =41.78% of %deltaSUVmean was used as threshold value, AUC was 0.923 (P = 0.0001). The sensitivity and specificity were 100%, 76.9%, respectively.

CONCLUSION

F-18 FDG PET/CT is useful for discrimination of residual and nonresidual SI after treatment. Among the various quantitative indexes, %deltaSUVmax is a potent predictor of residual SI in the current study.

Radiographic imaging in osteomyelitis: the role of plain radiography, computed tomography, ultrasonography, magnetic resonance imaging, and scintigraphy

The diagnostic imaging of osteomyelitis can require the combination of diverse imaging techniques for an accurate diagnosis. Conventional radiography should always be the first imaging modality to start with, as it provides an overview of the anatomy and the pathologic conditions of the bone and soft tissues of the region of interest. Sonography is most useful in the diagnosis of fluid collections, periosteal involvement, and surrounding soft tissue abnormalities and may provide guidance for diagnostic or therapeutic aspiration, drainage, or tissue biopsy. Computed tomography scan can be a useful method to detect early osseous erosion and to document the presence of sequestrum, foreign body, or gas formation but generally is less sensitive than other modalities for the detection of bone infection. Magnetic resonance imaging is the most sensitive and most specific imaging modality for the detection of osteomyelitis and provides superb anatomic detail and more accurate information of the extent of the infectious process and soft tissues involved. Nuclear medicine imaging is particularly useful in identifying multifocal osseous involvement.

Nuclear medicine and the infected joint replacement

Nearly 700,000 hip and knee arthroplasties are performed annually in the United States. Although the results in most cases are excellent, implants do fail. Complications like heterotopic ossification, fracture, and dislocation are now relatively rare and easily diagnosed. Differentiating aseptic loosening, the most common cause of prosthetic joint failure, from infection, is important because their treatments are very different. Unfortunately, differentiating between these 2 entities can be challenging. Clinical signs of infection often are absent. Increased peripheral blood leukocytes, erythrocyte sedimentation rate, and C-reactive protein levels are neither sensitive nor specific for infection. Joint aspiration with Gram stain and culture is the definitive diagnostic test. Its specificity is in excess of 90%; its sensitivity is variable, however, ranging from 28% to 92%. Plain radiographs are neither sensitive nor specific and cross-sectional imaging modalities, such as computed tomography and magnetic resonance imaging, can be limited by hardware-induced artifacts. Radionuclide imaging is not affected by orthopedic hardware and is the current imaging modality of choice for suspected joint replacement infection. Bone scintigraphy is sensitive for identifying the failed joint replacement, but cannot be used to determine the cause of failure. Neither periprosthetic uptake patterns nor performing the test as a 3-phase study significantly improve accuracy, which is only about 50-70%. Thus, bone scintigraphy typically is used as a screening test or in conjunction with other radionuclide studies. Combined bone gallium imaging, with an accuracy of 65-80%, offers only modest improvement over bone scintigraphy alone. Presently, combined leukocyte/marrow imaging, with approximately 90% accuracy, is the radionuclide imaging procedure of choice for diagnosing prosthetic joint infection. In vivo leukocyte labeling techniques have shown promise for diagnosing musculoskeletal infection; their role in prosthetic joint infection has not been established. (111)In-labeled polyclonal immunoglobulin lacks specificity. (99m)Tc-ciprofloaxicin does not consistently differentiate infection from aseptic inflammation. (18)F-fluorodeoxyglucose positron emission tomography has been extensively investigated; its value in the diagnosis of prosthetic joint infection is debatable.

The role of conventional radiography and scintigraphy in the third millennium

Imaging represents a cornerstone for diagnosing and monitoring rheumatic diseases. In the last few years, with the availability of highly effective therapies, demand for the technical performance of imaging has increased exponentially, leading to rapid development of new technologies such as magnetic resonance imaging (MRI) and ultrasound (US). In both clinical practice and clinical trials, there is a need for tools that are sensitive to change and to therapy response, which are able to depict inflammatory changes early, before irreversible joint damage has occurred. Despite these advances, conventional radiography (CR) and bone scintigraphy (BS), the two oldest imaging tests, continue to provide enormous diagnostic and prognostic help for the study of many musculoskeletal disorders. Furthermore, CR is an inexpensive, widely available and reproducible tool for evaluating and monitoring structural damage. This chapter focuses on the roles of CR and BS in rheumatological clinical practice, taking into account their performance in comparison with the newer imaging techniques.

Shoulder arthroplasty

Shoulder prostheses are now commonly used. Clinical results and patient satisfaction are usually good. The most commonly used types are humeral hemiarthroplasty, unconstrained total shoulder arthroplasty, and semiconstrained inversed shoulder prosthesis. Complications of shoulder arthroplasty depend on the prosthesis type used. The most common complications are prosthetic loosening, glenohumeral instability, periprosthetic fracture, rotator cuff tears, nerve injury, infection, and deltoid muscle dysfunction. Standard radiographs are the basis of both pre- and postoperative imaging. Skeletal scintigraphy has a rather limited role because there is overlap between postoperative changes which may persist for up to 1 year and early loosening and infection. Sonography is most commonly used postoperatively in order to demonstrate complications (hematoma and abscess formation) but may also be useful for the demonstration of rotator cuff tears occurring during follow-up. CT is useful for the demonstration of bone details both pre- and postoperatively. MR imaging is mainly used preoperatively, for instance for demonstration of rotator cuff tears.

99mTc-HMPAO labelled white blood cell scintigraphy in patients with osteoarticular infection: the value of late images for diagnostic accuracy and interobserver reproducibility

The objectives of this study were to evaluate the diagnostic value of 99mTc-HMPAO labelled white blood cell scintigraphy (WBCS) in patients with suspected osteomyelitis using late images and to study interobserver reproducibility. This study prospectively included 120 patients, and after a follow-up of one year, only 70 patients (n = 49 with implants, n = 21 without implants) were selected. The final diagnosis of infection was based either on microbiological data (n = 54) or follow-up (n = 16). We performed WBCS with 4 h and 24 h scans. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 77%, 72%, 83%, 64%, and 75% at 4 h, and 74%, 87%, 91%, 59%, and 79% at 24 h, respectively. The interobserver reproducibility shows a 63% prevalence of agreement between results (kappa = 0.5) at 4 h and 80% (kappa = 0.74) at 24 h, respectively. WBCS with 24-h images improves specificity and interobserver reproducibility in patients with suspected osteoarticular sepsis.

Diabetic foot osteomyelitis: a progress report on diagnosis and a systematic review of treatment

The International Working Group on the Diabetic Foot appointed an expert panel to provide evidence-based guidance on the management of osteomyelitis in the diabetic foot. Initially, the panel formulated a consensus scheme for the diagnosis of diabetic foot osteomyelitis (DFO) for research purposes, and undertook a systematic review of the evidence relating to treatment. The consensus diagnostic scheme was based on expert opinion; the systematic review was based on a search for reports of the effectiveness of treatment for DFO published prior to December 2006. The panel reached consensus on a proposed scheme that assesses the probability of DFO, based on clinical findings and the results of imaging and laboratory investigations. The literature review identified 1168 papers, 19 of which fulfilled criteria for detailed data extraction. No significant differences in outcome were associated with any particular treatment strategy. There was no evidence that surgical debridement of the infected bone is routinely necessary. Culture and sensitivity of isolates from bone biopsy may assist in selecting properly targeted antibiotic regimens, but empirical regimens should include agents active against staphylococci, administered either intravenously or orally (with a highly bioavailable agent). There are no data to support the superiority of any particular route of delivery of systemic antibiotics or to inform the optimal duration of antibiotic therapy. No available evidence supports the use of any adjunctive therapies, such as hyperbaric oxygen, granulocyte-colony stimulating factor or larvae. We have proposed a scheme for diagnosing DFO for research purposes. Data to inform treatment choices in DFO are limited, and further research is urgently needed.

Diagnostic imaging tests and microbial infections

Despite significant advances in the understanding of its pathogenesis, infection remains a major cause of patient morbidity and mortality. While the presence of infection may be suggested by signs and symptoms, imaging tests are often used to localize or confirm its presence. There are two principal imaging test types: morphological and functional. Morphological tests include radiographs, computed tomography (CT), magnetic resonance imaging, and sonongraphy. These procedures detect anatomic, or structural, alterations produced by microbial invasion and host response. Functional imaging tests reflect the physiological changes that are part of this process. Prototypical functional tests are radionuclide procedures such as bone, gallium, labelled leukocyte and fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging. In-line functional/morphological tomographic imaging systems, PET/CT and single photon emission tomography (SPECT)/CT, have revolutionized diagnostic imaging. These devices consist of a functional imaging device (PET or SPECT) joined together with a CT scanner. The patient undergoes both tests sequentially without leaving the examination table. Images from each study can be viewed separately and as fused images, providing precisely localized anatomic and functional information. It must be noted, however, that none of the current morphological or functional tests, either alone or in combination, are specific for infection and the goal of finding such an imaging test remains elusive.

Magnetic Resonance Imaging of Appendicular Musculoskeletal Infection

Appendicular skeletal infection includes osseous and extraosseous infections. Skeletal infection needs early diagnosis and appropriate management to prevent long-term morbidity. Magnetic resonance imaging is the best imaging modality to diagnose skeletal infection early in most circumstances. This article describes the role of magnetic resonance imaging in relation to the other available imaging modalities in the diagnosis of skeletal infection. Special circumstances such as diabetic foot, postoperative infection, and chronic recurrent multifocal osteomyelitis are discussed separately.