Ultrasonography in rheumatoid arthritis: what rheumatologists should know

Abstracts

Recentemente, a ultrassonografia vem ganhando prestígio como método adjuvante no diagnóstico e no acompanhamento terapêutico da artrite reumatoide, embora a radiografia ainda seja a modalidade de imagem tradicionalmente utilizada em larga escala com esses propósitos. O grande trunfo do estudo ultrassonográfico, que vem motivando pesquisas entusiastas na área, reside em sua capacidade de detectar sinovite e erosão óssea em fase pré-radiográfica, o que tem sido cada vez mais valorizado na prevenção do dano estrutural tardio e definitivo. Por ser um assunto relativamente novo, vários artigos científicos vêm sendo publicados em anos recentes sobre as potenciais aplicações da ultrassonografia em portadores de artrite reumatoide, alguns voltados a pesquisadores, outros voltados ao reumatologista clínico. O objetivo deste artigo é depurar a bibliografia atualmente disponível e descrever apenas os conceitos de aplicabilidade prática na rotina diária do reumatologista clínico.

ultrassonografia; artrite reumatoide; revisão; ultrassonografia Doppler

REVIEW ARTICLE

Ultrasonography in rheumatoid arthritis: what rheumatologists should know

Carlos Frederico Arend

Radiologist, Radimagem Diagnóstico por Imagem, Porto Alegre, RS, Brazil

^{Correspondence to}

ABSTRACT

Ultrasonography has recently gained prestige as an adjuvant method for the diagnosis and therapeutic follow-up of rheumatoid arthritis, although radiography remains the imaging modality traditionally and widely used for those purposes. The great advantage of the ultrasonographic study, which has motivated enthusiastic research in the area, resides in its capacity to detect synovitis and bone erosion at a pre-radiographic phase, which has been increasingly valued in preventing late and definitive structural damage. Because that is a relatively new subject, several scientific articles have been published in recent years about the potential applications of ultrasonography in individuals with rheumatoid arthritis, some of which directed to researchers and others to clinical rheumatologists. This study aimed at assessing the currently available bibliography on the subject and at describing only the concepts that are of practical applicability in the daily routine of clinical rheumatologists.

Keywords: ultrasonography, rheumatoid arthritis, review, color Doppler ultrasonography.

INTRODUCTION

Rheumatoid arthritis (RA) is a multifactorial, symmetric, peripheral, chronic polyarthritis, whose prevalence is estimated as 1% of the population. The synovial membrane is the target structure of the autoimmune attack. Most patients have a cyclic course of clinical remissions and relapses, which tends to result in progressive joint destruction and deformity. Radiography has been traditionally used in the search for imaging diagnostic criteria and in patients' follow-up. However, radiographically demonstrable findings, such as joint space reduction, subluxation, or bone erosion, represent irreparable anatomic changes. However, specialized literature has recently recommended an emphasis on RA screening and early treatment, aimed at preventing the progression to irremediable late deformity.¹ The theoretical motivation for searching for an early diagnosis lies in the greater metabolic activity of the disease's early stages.² That phase represents an important window of opportunity to prevent definitive structural damage. Ultrasonography enables the specific follow-up of that group of patients, by demonstrating pre-radiographic changes still at a reversible phase or even already irreversible small changes. As an alternative, magnetic resonance imaging can also detect initial RA changes, but with its inherent limitations of cost and availability (Table 1).

Because that is a relatively new subject, several scientific articles have been published in recent years about the potential applications of ultrasonography in individuals with RA, some of which directed to researchers and others to clinical rheumatologists. This study aimed at assessing the currently available bibliography on the subject and at describing only the concepts that are of practical applicability in the daily routine of clinical rheumatologists.

ULTRASONOGRAPHY FOR ASSESSING SYNOVITIS

Synovitis, either proliferative or exudative, is the earliest change that can be ultrasonographically graded. Its quantification via grayscale ultrasound usually uses a semiquantitative scale with three levels of intensity, indicating mild, moderate or marked synovial changes^3,4 (Figure 1).

On imaging, proliferative synovitis manifests as distension of the articular capsule by a poorly compressed, hypoechoic tissue, which initially tends to establish in the following joints: metacarpophalangeal, metatarsophalangeal or proximal interphalangeal (Figure 2 A and B). The search for occasional synovial vascularization on color or power Doppler imaging is very useful complementary information for therapeutic monitoring, because increased blood flow is present during the active phase of disease. In addition, spectral analysis of the pathologic flow reveals a pattern of low resistance in the acute active phase and elevated resistance in the chronic active phase^5-8 (Figure 2 E, F and G). The cutoff point of the several quantitative indices to characterize high or low resistance is currently controversial and object of much study in the literature, although an absent or reverse diastolic flow surely indicates high resistance.

 

Although proliferative synovitis and exudative synovitis (joint effusion) can only be differentiated via gray scales in last-generation equipment (Figure 3 A, B and C), in most cases the major diagnostic clue is synovial fluid compressibility (Figure 3, D, E and F). An insignificant amount of fluid in the plantar or dorsal recess of metatarsophalangeal joints is a normal finding, which should not be considered pathological.

 

Synovitis of the distal radioulnar joint, usually extending to the ulnar styloid process and contiguous structures, is such a characteristic finding that it is even considered pathognomonic of RA (Figure 4 A and B). Usually, but not always, the change is bilateral. On the dorsal face of the intercarpal joints, that finding is equally considered typical (Figure 4 C and D). Synovitis can also affect synovial sheaths. In fact, the histopathological analysis of the synovial tendon sheath reveals an incredible similarity with that of the joint synovium in individuals with RA, including hyperplasia of the lining cells and leukocyte infiltration, mainly CD4+ T cells and CD68+ macrophages.⁹ Thus, the differential diagnosis with systemic inflammatory arthropathy should be considered in the presence of synovitis in unusual sheaths, rarely associated with trauma or overuse, such as that of the long flexor of the thumb (Figure 4 E and F), extensor carpi ulnaris, and flexor carpi radialis (Figure 4 G and H). Distally, the most affected sheaths are those of the extensor tendons of the second and third fingers.^10-12 Synovitis in the tendon sheaths of the toes is rare, being usually associated with systemic inflammatory arthropathy, either in the flexor (Figure 4 I and J) or extensor (Figure 4 K and L) region.

 

Ultrasonography can be used to monitor the response to treatment by assessing the reduction in synovitis intensity on the grayscale test and/or in synovial vascularization by use of color or power Doppler imaging.¹³ Several ultrasonographic scores of synovial impairment have been proposed in the literature and all have been mainly aimed at detecting changes in the inflammatory activity by assessing the smallest possible number of joints to reduce the time of exam.^14-18 In our opinion, such protocols are still primarily aimed at the communication between researchers, their use on routine clinical practice being based on fragile scientific evidence. Ultrasonographic contrast media have also been tested in the search for a better differentiation between active and inactive synovitis, but their use is equally experimental and should not be incorporated to routine clinical practice, at least for now.¹⁹

ULTRASONOGRAPHY FOR ASSESSING BONE EROSION

Bone erosion results from the colagenase produced on the interface between synovium, bone and joint cartilage, typically observed in the periphery of the joint space, where bone is not covered by cartilage.²⁰ Erosions develop predominantly during the first two years of disease (in aggressive disease, in the first 6 months)²¹ and have a marked predilection for the ulnar styloid process, capitate bone, pyramidal bones, semilunar bones, and radial face of the second and third metacarpophalangeal joints, most notably in the head of metacarpal bones²² (Figure 2 C and D). Because of the ease of access, the search for erosions in the margins of the metacarpophalangeal and metatarsophalangeal joints of the first and fifth fingers is probably more accurate than the study of the other toes and fingers, which do not allow satisfactory medial and lateral access. It is worth noting that, when assessing the dorsal face of the head of metacarpal and metatarsal bones, a small anatomic bone indentation usually present in those regions should not be considered an erosion²³ (Figure 5).

Semiquantitative scores for different degrees of erosion have already been published aiming at treatment monitoring,^24-27 but they still require more comprehensive studies, confirming their accuracy and reproducibility. In accordance with the literature, we observed that the clinical remission of RA under treatment is usually accompanied by an improvement in synovitis, but not in the erosions already formed.

ULTRASONOGRAPHY FOR THE DIFFERENTIAL DIAGNOSIS OF RHEUMATOID ARTHRITIS

The ultrasonographic documentation of synovitis or bone erosion does not exclusively indicate the diagnosis of RA in its early phase. In fact, spontaneous resolution is observed in half of the cases of synovitis with less than 6 months of evolution.^28,29 In the other half, the course tends to be of a chronic and persistent disease. Some patients with chronic and persistent disease develop full criteria for RA, while others remain with the diagnosis of undifferentiated arthritis. In screening incipient RA, it is worth noting that it should be differentiated from undifferentiated arthritis and other inflammatory polyarthralgias in their initial phase, mainly psoriatic arthritis and systemic lupus erythematosus, whose findings might be similar with identical distribution.^23,30-32 When present, both subcutaneous edema^33-35 and bone erosion in the margins of the distal interphalangeal joint ^36,37 suggest psoriatic arthritis as the initial hypothesis. The lack of such findings, however, does not contribute to the differential diagnosis. Based on clinical and serological characteristics, it is currently possible to predict with good accuracy which patients with undifferentiated arthritis will progress to RA, a task much better performed by the attending physician than by the ultrasonographist.³⁸

CONCLUSION

Ultrasonography has recently gained prestige as an adjuvant method for the diagnosis and therapeutic follow-up of RA, although radiography remains the imaging modality traditionally and widely used for those purposes. The great advantage of the ultrasonographic study, which has motivated enthusiastic research in the area, resides in its capacity to detect synovitis and bone erosion at a pre-radiographic phase. That generates information that can be used for diagnostic or therapeutic purposes, with a potential impact on the patients' quality of life.

REFERENCES

Received on 11/08/2011.

Approved on 11/26/2012.

The author declares no conflict of interest.

Radimagem Diagnóstico por Imagem, Porto Alegre, RS, Brazil.

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Publication Dates

• Publication in this collection
  09 Apr 2013
• Date of issue
  Feb 2013

History

• Received
  08 Nov 2011
• Accepted
  26 Nov 2012