© Borgis - Postępy Nauk Medycznych 2/2012, s. 164-169
*Małgorzata Wisłowska, Magdalena Matryba
Badania obrazowe w diagnostyce i ocenie leczenia chorych na reumatoidalne zapalenie stawów
Imaging methods in diagnosis and evaluation of treatment of rheumatoid arthritis patients**
Rheumatology and Internal Medicine Clinic of Central Hospital of the Ministry of Internal Affairs
Head of Department: prof. Małgorzata Wisłowska, MD, PhD
Podstawowym badaniem obrazowym w diagnostyce reumatoidalnego zapalenia stawów jest tradycyjna radiografia. Dla dokładnej oceny progresji zmian stawowych stosowana jest zmodyfikowana metoda Sharpa oraz metoda Larsena-Dale’a. Nasilenie zmian radiologicznych koreluje z aktywnością choroby i upośledzeniem funkcji stawów. Badanie ultrasonograficzne to metoda oceny struktur stawów, w tym tkanek miękkich układu ruchu. Badanie przepływu naczyniowego w błonie maziowej stawów przy użyciu tzw. Dopplera mocy umożliwia ocenę angiogenezy w zapalnie zmienionych stawach i koreluje z aktywnością procesu zapalnego. Tomografia komputerowa pozwala na znacznie wcześniejsze wykrycie zmian niż tradycyjna radiografia. Obrazowanie metodą rezonansu magnetycznego umożliwia dokładną ocenę tkanek miękkich i kości oraz wielopłaszczyznowe obrazowanie struktur zlokalizowanych w głębi ciała, takich jak stawy szczytowo-potyliczne i szczytowo--obrotowe oraz zmian pozastawowych – dotyczących głównie układu nerwowego, naczyń, powięzi i mięśni.
Conventional radiography is a common imaging method in diagnosis of rheumatoid arthritis. Modified Sharp method and Larsen-Dale method are applied for accurately scoring of joint damages. Intensity of radiological destructive changes are correlated with disease activity and deterioration of joints function. Ultrasonography is the method of evaluation of joints structures, especially soft tissue of movement system. Evaluation of flow in vessels in synovium using Power Doppler enables to estimate angiogenesis in inflammatory joints and is correlated with disease activity. Computed tomography allows to detect destructive changes more early than conventional radiography. Magneting resonance imaging allows accurate evaluation of soft tissues and bones and multilevel imaging of structures localized inside body as atlantooccipital and atlantoaxial joints and extra-articular changes - concerned mainly nervous system, vessels, fascia and muscles.
Imaging used in diagnosis and evaluation of treatment of rheumatoid arthritis (RA) patients includes the following types of examination: radiological, ultrasonographic, scintigraphic, tomographic and magnetic resonance imaging. Imaging allows early diagnosis of RA, even in the symptomless stage, and prompt commencement of treatment. If the treatment begins in the initial phase of the disease, there is a high chance of inhibition of its activity or even, in some cases, of total remission. Moreover, appropriately conducted imaging allows to forecast disease acuteness, to monitor its course and effectiveness of applied treatment.
Traditional radiography is the basic imaging technique used in diagnosis of rhematoid arthritis (RA). In every case of suspected RA, images of hands in AP projection and feet in AP and LL projections should be taken. That should show the tuber calcanei and the head of the fifth metatarsal bone. Another image should include the cervical vertebrae in the lateral projection (neutral position), due to possibility of dangerous complications in a form of a dislocated odontoid process. In cases when the diagnosis is known, additional imaging includes pictures of clinically involved joints (1). Comparative X-ray images, that is pictures of two symmetrical body regions made on the same X-ray film, are of high value.
Radiological examination reflects the course of a disease. However, sometimes in case of patients with acute inflammatory process no essential changes are visible and vice versa. Inhibition or decreased progress of radiological changes means that activity of a disease between subsequent X-ray examinations was low (2).
X-ray examination of patients suffering from RA allows to diagnose swelling of soft tissue in periarticular areas caused by vasculitis of the synovial membrane and adjoining soft structures. That swelling is particularly visible in the surrounding of hand and foot joints. Occurrence of juxta-articular osteoporosis caused by topical congestion of bone and increased inflammatory bone resorption is also visible in X-ray images, as well as narrowing of joint gaps caused by destruction of joint cartilages. Another typical symptom of RA is occurrence of destructive lesions caused by growth of inflammatory granulation tissue (so called pannus) within the synovial membrane and intratrabecular spaces of cancellous bone heads. Initially, those changes occur in the subchondral layer of trabecular bones in a form of inflammatory geodes. Subsequently they cause occurrence of erosion. Those initially occur within the articular capsule, on the surface of bone deprived of joint cartilage as so called border erosion. Due to their gradual expansion, head bones become destroyed. Damage of joint surfaces causes their total consolidation, occurrence of bone and fibrous adhesion (so called ankylosis) with limited mobility of joints. That symptom mainly occurs in phalangeal and carpal articulations. X-ray images also show other types of joint deformations: ulnar deviation in metacarpophalangeal joints and lateral deviation in metatarsophalangeal joints, subluxations, contractures of articulations caused by damage in the ligamento-capsular apparatus and muscle attachments or genu valgum, being a symptom of damage to the lateral part of the joint cartilages. Moreover, RA also causes osteolysis of bone fragments, most frequently affecting phalanges of hands and feet, yet possibly also including the acromial end of the clavicle, the distal end of the radius and the ulna bones and the spinous process of the cervical vertebrae. A lateral image of the calcaneus can demonstrate irregular, fuzzy outline of the posterior part of the tuber calcanei caused by bursitis of the Achilles tendon. In case of subluxation in the atlanto-axial joint, lateral X-ray images of bent head show increased (> 3 mm) distance between the odontoid process (dens) and the arch of the atlas vertebra. Another consequence of such pathological lesions in atlanto-axial joints can be indentation in the base of the skull. To date, two lines have been used to assess such changes: Chamberlain’s line (a line drawn from the craniovertebral junction joining the posterior end of the hard palate to the posterior lip of the foramen magnum) and McGregor’s line (a line drawn from the posterior edge of the hard palate to the most posterior point of the occiput). Position of the apex of the odontoid process in relation to those lines describes the degree of indentation. In normal conditions, the apex should not reach beyond Chamberlain’s line more than 3 mm and McGregor’s line more than 5-6 mm. Sakaguchi and Kauppi suggested a much simpler and easier method to assess indentation. Their method traces a line which connects inferior edge of the anterior arch with the inferior outline of the posterior arch of the atlas. Projection of the atlanto-axial joints should be located below that line. Such method does not require any measurements (1).
According to Steinbrocker’s criteria, intensification of destructive lesions in articulations is described in four stages (3). Early stage I is a protuberance of soft periarticular parts and periarticular osteoporosis. At moderate stage II, symptoms include narrowing of joint gaps and formation of subchondral geodes, as well as osteoporosis. Advanced changes of stage III include frequent erosion of joint surfaces, osteoporosis and joint deformation in various forms: subluxation, ulnar deviations, hypermobility. In the terminal stage IV, bone or fibrous adhesion occur, accompanied by the same changes as during the stage III.
Assessment of joint changes according to Larsen-Dale (4) comprises 6 stages: stage 1 is a normal picture of a joint. Stage 2 describes appearance of minor changes: periarticular edema of soft tissues, juxta-articular osteoporosis, slight narrowing of joint gaps. Stage 2 also means early erosion and narrowing of joint gaps, while stage 3 means average destructive changes such as erosion and narrowing of joint gaps. Stage 4 is described as large destruction to the surface of joints. Stage 5 occurs when significant deformation of articulations can be observed.
Modified Sharp’s and Larsen-Dale’s methods are used for accurate assessment of progression in joint changes. Sharp’s method assesses the number of erosion occurrences and degree of narrowing of the joint gaps in arms, wrists and feet (5). Occurrences of erosion in arm joints are assessed in 0 out of 5 scale, while 0 out of 10 scale is used for foot joints and 1 out of 4 scale is applied to assessment of joint gap narrowing. The maximal score for occurrence of erosion in one patient is 280 (arms – 160, feet – 120), while the maximal score for narrowing is 168 (arms – 120, feet – 48). Hence the total score while using this method is 448. Larsen-Dale’s method is based on reference films. The degree of progression is assessed on their basis with use of a 5-stage scale in 32 joints of hands, wrists and feet. The degree of progression corresponds to the number of points scored, while points scored for the wrist are multiplied by 5. The total Larsen Score (LS) is calculated as a sum of points obtained for each joint. The maximal score (called Larsen-Dale’s index) for one patient is 200. Moreover, in case of patients with a diagnosed form of RA, radiological progression expressed with use of one of the above described methods, which assess arm and foot joints, indirectly reflects changes in large articulations. However, those methods cannot be reliably used in patients with early stages of arthritis, as in that case it is possible that other than assessed joints become affected by the disease. The percentage of patients affected with erosion of arm and foot joints, as diagnosed during the first radiological examination, is estimated as low as 15% (2). Another estimation is that probably 70% of patients diagnosed with undifferentiated arthritis, rather than rheumatoid arthritis, do not show symptoms of progression of radiological changes nor occurrence of erosion (6).
Intensification of radiological changes correlates with activity of the disease and impairment of joint functionality. The most rapid development of erosion occurs in the first two years of the disease progress. It was found that frequency of erosion cases increases up to 28% within the first 12 months since the first occurrence of RA symptoms (7). Subsequently, it was calculated that average annual increase of the maximum joint damage, that is the case when the degree of erosion reaches the maximum and the joint gaps become the narrowest, amounts to 1.9%. During the first 2 years, the average value of Larsen’s index scores between 8 and 17% of the maximal possible damage. After 5 years, changes assessed with use of Sharp’s method gave the maximal score in case of 14% patients, while after 20 years that percentage is as high as 43 (1).
Ultrasonography is a method of assessment of joint structures which includes examination of the soft tissues of the locomotor system. That imaging technique uses the reflected ultrasonic wave with frequency over 20 000 Hz (20 kHz), i.e. returning echo, which is then analyzed in terms of location and intensity. Ultrasonographic examination has many advantages: it is non-invasive, harmless and non-intrusive for the patient. Examination can be conducted in virtually any place, for example at the patient’s bed. Ultrasonography is widely available and quite inexpensive. Obtained images feature high spatial resolution and contrast, can be recorded in real time, during movement. The examination is possible during passive and active movement of the patient, allows simultaneous puncture and monitoring of treatment response (8, 9).
Ultrasonography allows to diagnose occurrence of erosion earlier than in case of traditional radiography because it enables simultaneous assessment of core layers of joint bones in many planes, also during dynamic examination with their passive bending and straightening. In normal conditions, the bone outlines are smooth, covered with a layer of anechoic cartilage. In case of patients with active inflammatory process, joint surfaces become irregular, uneven and worn. Erosion becomes visible as losses in the bone outline with various sizes and depths, filled during intensified inflammatory state of RA progression with hypoechogenic pannus mass, often with visible vessels penetrating the bone. It was estimated that an ultrasound examination allows to detect from 1.4 to 3.5 times more erosion occurrences than a classic X-ray image of arms (8, 9).
Normal synovial membrane is invisible during an ultrasound examination. However, it allows to detect inflammatory changes in structures which include the synovium (articular capsules and bursae, tendon sheaths). That usually demonstrates various stages of hypertrophy with presence of hypoechogenic tissue foci and effusion). It also allows to assess the state of muscles and ligaments. Research conducted on a larger number of both symptomatic and asymptomatic joints proved ultrasound examination to detect synovitis in 79% cases of edemal, 33% cases of only painful and in 13% of clinically normal articulations (10). In case of RA progression, the earliest visible symptoms include inflammatory changes in the synovial membrane of the metacarpophalangeal, proximal interphalangeal and metatarsophalangeal joints, while in case of children it also affects large joints, frequently knees. In case of the inflammation of tendon sheaths, it is possible not only to see thickening and the degree of vascularization of tendons but also assess their mobility and degree of damage. Due to adhesion with the sheath or inflammation-induced pressure, mobility of the tendon is limited. Changes in tendons demonstrate themselves as dilation or thinning, irregularities and losses in their fibrous structure, occurrence of cysts, strain or tear in their continuity. It may be accompanied by an increased vascular flow related to the ingrowth of the synovial membrane vessels into the tendons. Ultrasound examination also enables differentiation of fluid collection (effusion) from hypertrophy of the synovial membrane. That allows to perform aimed punctures for diagnostic and therapeutic purposes, during which it is possible to evacuate the fluid or administer corticosteroids into the joints. Ultrasound examination also allows for controlled biopsy of pannus and joint erosion (11). Ultrasonic images of inflammatory changes are non-specific in relation to their causes.
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