Technetium-99m labelled human immunoglobulin scintigraphy predicts rheumatoid arthritis in patients with arthralgia

Update on Imaging of Inflammatory Arthritis and Related Disorders

Arthritis and other rheumatic disorders are very frequent in the general population and responsible for a huge physical and disability burden to affected patients as well as a major cost to the society. Precise evaluation often relies on clinical data only but additional imaging may be required i) for a more objective assessment of the disease status, such as in rheumatoid arthritis (RA) or ankylosing spondyloarthritis (AS), ii) for providing prognostic information and evaluating response to treatment or iii) for establishing diagnosis, in patients with unclear clinical picture, such as polymyalgia rheumatica (PMR) and large-vessel vasculitis (LVV). Besides radiological techniques (x-rays, ultrasound, and MRI), functional and molecular imaging has emerged as a valid tool for this purpose in several disorders. Bone scanning has long been a method of choice but is now more used as a triage tool in patients with unclear complaints, including degenerative disorders (eg osteoarthritis). ¹⁸F-FDG-PET/CT (FDG) proved efficient in assessing the extent of the disease and response to treatment in RA and related disorders, and to provide accurate diagnosis in some systemic disorders, including PMR and LVV. Based on glucose metabolism, FDG-PET/CT is able to show increased metabolism in peripheral cells involved in inflammation (eg neutrophils, lymphocytes or monocytes/macrophages) but also in fibroblasts that proliferate in the pannus. The lack of specificity of FDG is a limitation and many alternative tracers were developed at the preclinical stage or applied in the clinics, especially within clinical trials. They include imaging of macrophages using translocator protein (TSPO), folate-receptors or other targets on activated cells. These new tools will undoubtedly become more and more available in the everyday clinical workup of patients with rheumatisms. Finally, it should be kept in mind that a very simple tracer, ¹⁸F-fluoride is widely more performant in AS than FDG.

Molecular Imaging of Inflammatory Arthritis and Related Disorders

Rheumatic disorders comprise a number of diseases that range from benign, mildly symptomatic degenerative disease to severe systemic disorders such as giant-cell vasculitis with dramatic consequences such as acute blindness. The former is relatively common, whereas the latter is rare. In between, commonly encountered disorders such as rheumatoid arthritis and the various spondyloarthritides, with or without peripheral enthesitis, are daily challenges for the caring physician. Clinical evaluation is of utmost importance and is constantly described under the form of specialist guidelines in all parts of the world. Objective assessment of inflammatory arthritis and related disorders is of interest both for the care of the individual patient and for the assessment of the effects of the many novel experimental therapies proposed in this field, most of them being very expensive. High-resolution ultrasound, CT and spectral CT, MRI using various sequences, and molecular imaging using either gamma camera imaging (including SPECT-CT) or PET-CT are all proposed for a better assessment of these diseases. This review focuses on the several nuclear medicine techniques that are or may become useful to helping provide better patient care in this field and is mainly oriented to inflammatory rheumatic disorders, excluding mechanical degenerative diseases.

Which patients presenting with arthralgia eventually develop rheumatoid arthritis? The current state of the art

Early initiation of treatment in patients with inflammatory arthritis at risk of persistence and/or erosive progression is important because it is associated with a reduced rate of progression of joint damage and functional disability. It has been proposed that a window of opportunity exists, during which disease processes are less matured and disease modification can be more effective. The phase of arthralgia preceding clinical arthritis is likely to be an important part of this window of opportunity, during which treatment might prevent progression to clinical arthritis. Several proof-of-concept trials in individuals with arthralgia are now evaluating this hypothesis. Central to such trials is the ability to identify groups at high risk of rheumatoid arthritis (RA) in whom preventive treatment can be tested. This review describes the relevance of adequate prediction making, as well as the accuracy of different types of predictors (including imaging and serological markers) with their value in predicting the progression of arthralgia to arthritis. Despite promising results, studies have been performed in heterogeneous patient populations and most findings have not been validated in independent studies. Future observational or preventive studies should be conducted with homogeneous patient groups (eg, patients fulfilling the European League Against Rheumatism criteria for arthralgia at risk of RA) in order to increase interstudy comparability and to allow result validation.

Diagnosis and management of rheumatoid arthritis; What is the current role of established and new imaging techniques in clinical practice?

Ultrasound and magnetic resonance imaging (MRI) have become established imaging techniques for the management of rheumatoid arthritis. Several publications have pointed out the advantages of these techniques for a more complete evaluation of the inflammation and structural damage at joint level. Recently new imaging techniques as the positron emission tomography (PET) associated with computed tomography (CT) or MRI scan, and the optical imaging have been introduced in the panorama. This article presents the advantages and limitations of each imaging techniques in light with the recent publications.

Prediction of future rheumatoid arthritis

Rheumatoid arthritis (RA) results from an interaction between genetic susceptibility and environmental factors. Several of these factors are known, such as family history of RA, high birth weight, smoking, silica exposure, alcohol nonuse, obesity, diabetes mellitus, rheumatoid factor, anti-citrullinated protein antibody, and genetic variants such as the shared epitope and protein tyrosine phosphatase nonreceptor type 22. The impact of these factors can be modeled in the 2 main groups at risk of RA: family members of patients with RA and seropositive persons with or without arthralgia. Current models have the potential to select individuals for preventive strategies.

Nuclear imaging of rheumatic diseases

Advanced imaging techniques are promising tools to assist in the early diagnosis and monitoring of therapy in various rheumatic diseases. As there is now increasing emphasis on diagnosing inflammatory rheumatic disease in the pre-clinical stages, so that treatment may be instituted early and ideally prevent irreversible tissue damage, highly sensitive techniques are needed to detect subclinical inflammation. Moreover, there is an increasing need to develop individualised treatment protocols at reasonable cost and with optimal therapeutic effect. Tools are required that can image the therapeutic target and sensitively trace changes in disease activity. Nuclear imaging techniques have the potential to fulfil these clinical needs. Positron emission tomography is emerging as an important modality as it provides highly sensitive, quantitative imaging at a molecular level, to reveal the important pathophysiological processes underlying inflammation. This chapter provides an overview of currently available nuclear imaging techniques, including recent technical developments, and discusses their role in the diagnosis and monitoring of rheumatic disease.

Macrophage positron emission tomography imaging as a biomarker for preclinical rheumatoid arthritis: findings of a prospective pilot study

OBJECTIVE

To conduct a prospective pilot study to determine whether macrophage targeting by 11C-(R)-PK11195 positron emission tomography (PET) can visualize subclinical synovitis in arthralgia patients who have anti-citrullinated protein antibodies (ACPAs).

METHODS

Twenty-nine arthralgia patients who were positive for ACPAs but did not have clinical arthritis were studied. High (spatial)-resolution 11C-(R)-PK11195 PET scans of the hands and wrists were performed. For all metacarpophalangeal, proximal interphalangeal, and wrist joints (i.e., 22 joints per patient), tracer uptake was scored semiquantitatively (0-3 scale) by 2 observers who were blinded with regard to the clinical data. Patients were followed up prospectively for 24 months to investigate the development of clinical arthritis.

RESULTS

Overall agreement and kappa values for the readings of the 2 observers were, respectively, 97% and 0.91 (95% confidence interval [95% CI] 0.74-1) at the patient level and 99% and 0.81 (95% CI 0.65-0.96) at the joint level. In 4 patients, at least 1 and as many as 5 PET-positive joints (score≥1) were found at baseline. Within 2 years of followup, 9 patients had developed clinical arthritis. This included all 4 patients with positive findings on the 11C-(R)-PK11195 scan, who developed clinical arthritis in the hand/wrist region, as identified on PET scans. Of the 5 remaining arthritis patients with negative findings on PET scans, 2 developed arthritis in the hand joints and 3 developed arthritis at locations outside the field of view of the PET scanner.

CONCLUSION

Subclinical arthritis in ACPA-positive arthralgia patients could be visualized by 11C-(R)-PK11195 PET scanning and was associated with development of arthritis within 2 years of followup. This indicates that 11C-(R)-PK11195 PET may be useful in determining arthritis activity in the preclinical phase of RA.

Anti-citrullinated peptide antibody assays and their role in the diagnosis of rheumatoid arthritis

Increasingly, assays for the detection of anti-citrullinated peptide antibodies (ACPA) are used in RA diagnosis. This review summarizes the biologic basis and development of ACPA assays, available ACPA assays and their performance characteristics, and diagnostic properties of ACPA alone and compared to rheumatoid factor (RF) in early RA. We also review correlations, precision, costs and cost-effectiveness, availability, stability and reproducibility of the available assays. Taken together, data indicate that ACPA has a higher specificity than RF for early RA, good predictive validity, high sensitivity, apparent cost-effectiveness and good stability and reproducibility. Given its superior performance characteristics and increasing availability, ACPA is emerging as the most useful single assay for the diagnosis of RA.

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.

Scintigraphy in rheumatic diseases

The aim of this review is to summarise the clinical role of nuclear medicine in rheumatology taking into consideration the most specific diagnostic applications and other worthwhile therapeutic contributions. Traditional bone scintigraphy and recent inflammation-targeting radiopharmaceuticals, such as radiolabelled leucocytes and immunoscintigraphy, now allow us to obtain highly sensitive total-body and tomographical imaging information that can be used for the diagnosis of osteoarticular disease. The most common extra-articular manifestations of rheumatic diseases due to digestive, central nervous, respiratory and cardiovascular system involvement can be diagnosed by specific scintigraphic methods. Radiosynovectomy plays an important role in providing effective treatment for some joint diseases that are resistant to pharmacological therapy. Diagnostic and therapeutic applications of nuclear medicine show the highest efficacy in the early phase of rheumatic diseases. In more advanced stages, scintigraphical techniques play a complementary role to radiographical investigations in the assessment of prognosis and therapy efficacy.

Folate-targeted imaging of activated macrophages in rats with adjuvant-induced arthritis

OBJECTIVE

To determine whether overexpression of the high-affinity folate receptor (FR) on activated macrophages can be exploited to selectively target imaging agents to sites of inflammation in rats with adjuvant-induced arthritis (AIA).

METHODS

Folic acid was conjugated to a (99m)Tc chelator (the complex termed EC20), and its distribution was visualized using gamma scintigraphy in healthy rats, rats with AIA, and arthritic rats that had been depleted of macrophages. To confirm that uptake was mediated by the FR, excess folic acid competition studies were conducted, and tissue FR levels were quantitated using a radioligand binding assay. Flow cytometry was also used to investigate uptake of folate conjugates into macrophages of both arthritic and healthy rats.

RESULTS

EC20 concentrated in the arthritic extremities of diseased rats but not in the extremities of healthy rats. The intensity of images of affected tissues was greatly reduced in the presence of excess competing folic acid. The livers and spleens of arthritic animals also showed enhanced uptake of EC20 and increased levels of FR. Depletion of macrophages from arthritic animals reduced tissue FR content and concomitantly abolished uptake of EC20. In addition, macrophages isolated from livers of rats with AIA exhibited a significantly higher binding capacity for folate conjugates than did macrophages obtained from healthy rats.

CONCLUSION

Although EC20 is currently undergoing clinical evaluation for use in the imaging of ovarian carcinomas, the present results suggest that it may also be useful for assaying the participation of activated macrophages in inflammatory processes such as rheumatoid arthritis.

Immunomodulatory and anti-inflammatory effects of Kalanchoe brasiliensis

The immunomodulatory effect of juice obtained from leaves of Kalanchoe brasiliensis (Kb) on zymosan-induced inflammation was investigated. C57B110 mice received a subcutaneous injection of 150 microg zymosan in the footpad. After 7 days, there was an increase in footpad thickness from 176 +/- 4 to 236 +/- 9 x 10(-2) mm and in blood flow in the footpad area, monitored by 99mTc, from 98 +/- 4 to 694 +/- 59 counts per minute (cpm). Zymosan induced a severe infiltration of leukocytes into the articular tissues and a 13-fold increase in the adjacent popliteal lymph node (PLN) weight. Beginning 2 days after the injection, mice were treated daily for 5 days with different concentrations of lyophilised Kb juice dissolved in water. Treatment with 480 mg/kg/day reduced footpad thickness to 193 +/- 5 x 10(-2) mm, leukocyte infiltration and blood flow to 150 +/- 18 cpm in the footpad area. PLN weight in zymosan-injected mice decreased from 6.5 +/- 0.5 to 1.5 +/- 0.4 mg, similarly to the decrease after treatment with indomethacin (3 mg/kg/day). Flow cytometric analysis of lymph node cells showed an important reduction in B cell number in Kb-treated mice. Treatment over a period of 10 days was also effective at reducing zymosan-induced inflammation, even when started 7 days after injection. These data suggest anti-inflammatory and immunosuppressive effects of K. brasiliensis that may account for its popularity in folk medicine against rheumatic diseases.

Orthopedic pathology of the lower extremities: scintigraphic evaluation in the thigh, knee, and leg

Radionuclide imaging (RI) of the osseous and nonosseous structures of the thigh, knee, and leg provide important diagnostic and prognostic information upon which the orthopedic surgeon can base treatment planning and management decisions. 99mTc-MDP scintigraphy is essential in overuse injuries such as stress fractures and shin splints. RI is important in assessing complications of trauma. It is the only imaging modality able to assess the magnitude of physeal stimulus caused by femoral fractures and to predict a favorable or unfavorable outcome of leg length by semiquantitative analysis; SPECT imaging can detect and locate decreased metabolism associated with posttraumatic closure of the physeal plate to predict growth arrest and deformities. Three-phase bone imaging (TPBI) is essential to differentiate hypervascular from avascular nonunions and follow delayed union. In osteonecrosis of the knee, bone scintigraphy precedes radiography changes even in stage l of the disease. 99mTc-MDP and 99mTc-HIG imaging are powerful tools in determining the outcomes of osteoarthritis and rheumatoid arthritis, respectively. Bone scintigraphy can also detect chronic ligament and acute and chronic meniscal lesions. The combined use of TPBI, gallium-67 citrate imaging, and indium-111 or 99mTc-HMPAO labeled leukocytes is important to diagnose and differentiate acute from chronic osteomyelitis, and to detect infected knee prostheses. Thallium-201 chloride imaging and 99mTc-sestamibi imaging have an important role in the assessment of tumor response to chemotherapy and in the quantification of tumor viability.

Orthopaedic manifestations of systemic disease

Nuclear medicine studies can be initiated to detect or evaluate systemic diseases such as inflammatory arthritis or Paget's disease. This is usually because of the strengths of nuclear medicine studies such as high sensitivity, an ability to easily image the whole body, and typical diagnostic patterns of abnormalities. In other instances, a systemic disease may be incidentally suggested by a scintigram such as osteoporosis or hyperparathyroidism; or a focal abnormality such as a vascular necrosis may be detected that should indicate a systemic condition should be sought. Although most nuclear medicine studies have high sensitivity for disease, specificity is often less and, for a particular scan abnormality, several conditions may have to be considered. Familiarity with the varying patterns of abnormality associated with different disease is therefore vital to correct assessment.