EDU: Synovial Biopsies

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Here is an article on " Synovial Biopsies " .

Marilyn

Review

Are synovial biopsies of diagnostic value?

Barry Bresnihan

Department of Rheumatology, St 's University Hospital, Dublin,

Ireland

Arthritis Res Ther 2003, 5:271-278 doi:10.1186/ar1003

The electronic version of this article is the complete one and can be found

online at: http://arthritis-research.com/content/5/6/271

Received 14 July 2003

Accepted 18 August 2003

Published 2 October 2003

© 2003 BioMed Central Ltd

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Keywords: synovial biopsy, diagnosis, early arthritis, rheumatoid arthritis,

undifferentiated arthritis

Synovial tissue is readily accessible by closed needle or arthroscopic

biopsy. These techniques provide adequate tissue for most diagnostic

requirements. Examination of synovial tissue can assist in the diagnosis of

some joint infections, and in several atypical or rare synovial disorders.

Histological confirmation is not normally required for diagnosis of the

common forms of inflammatory arthritis, including rheumatoid arthritis (RA).

In patients with either established or early RA, immunohistological measures

of inflammation in synovial tissue are associated with clinical measures of

disease activity, may predict the clinical outcome, and change in response

to treatment. Surrogate markers of disease activity and outcome that have

been identified in synovial tissue include components of the cellular

infiltrate, and several mediators of inflammation and matrix degradation.

There is evidence that the very early introduction of disease-modifying

therapy inhibits progressive structural damage maximally. Clinicians

exploiting this 'window of opportunity' therefore require very early

indicators of the diagnosis and outcome in patients who present with an

undifferentiated inflammatory arthritis. Some immunohistological features

have been described that distinguish patients who are likely to develop

progressive RA and who might benefit most from early aggressive therapeutic

intervention. In this regard, the inclusion of pharmacogenomic and proteomic

techniques in the analysis of synovial tissue presents some exciting

possibilities for future research.

History of synovial biopsy in the diagnosis of arthritis

Early histopathological studies of rheumatoid arthritis (RA) were based on

tissue samples obtained at surgery or at postmortem examination. In 1932 a

technique for obtaining non-surgical synovial tissue for diagnostic

purposes, using a dental nerve extractor that was introduced into the joint

through a large-calibre needle, was first proposed [1]. The introduction of

this technique to clinical practice was never described. About 20 years

later, early experiences with needle biopsy of the synovium were published

[2,3]. It was suggested that the procedure was safe and practical for use in

both hospital wards and outpatient clinics. However, because of their wide

bore and the need for an incision, these prototype biopsy needles tended to

cause significant trauma to the penetrated tissues. In 1963, and

Pearson described a simplified 14-gauge needle that did not require a skin

incision [4]. They published their experience of 125 procedures, almost all

from the suprapatellar pouch of the knee joint, with a very high yield of

adequate tissue for analysis. No serious complications were encountered. For

about 30 years, the –Pearson needle, or a modification of it [5,6],

remained the instrument of choice when acquiring synovial tissue for

diagnostic or research purposes.

Arthroscopic techniques, which enable the selection of synovial tissue under

direct vision, were also developed primarily to assist in the diagnosis of

arthritis [7]. Early studies by rheumatologists suggested a lack of

association between the arthroscopic findings and clinical, laboratory and

radiological features of arthritis [8,9]. More recently there has been an

upsurge in the use of arthroscopic techniques by rheumatologists,

particularly those interested in the pathogenesis of arthritis and the

effects of new therapeutic strategies [10]. Initially, arthroscopy required

hospitalisation and a general anaesthetic. The production of

high-definition, small-bore arthroscopes (1–2.7 mm), and the development of

local and regional anaesthesia protocols [11,12], have permitted day-case

arthroscopy to move from the operating theatre to procedure rooms, and even

to the outpatient clinic [13].

Synovial biopsy in routine clinical practice

Synovial biopsy is not normally required for routine diagnostic or

therapeutic purposes in patients with established arthritis. However,

examination of synovial tissue can assist in the diagnosis of some joint

infections [14]. In acute bacterial arthritis, the synovial membrane

contains clusters or sheets of polymorphonuclear leukocytes. Bacteria can be

demonstrated in synovial tissue by Gram's stain. Sometimes, cultures of

synovial tissue may be positive even when blood and synovial fluid cultures

have been negative. In chronic infections, such as tuberculosis and fungal

diseases, characteristic synovial lesions may be focal, and multiple

biopsies are advised. Mycobacterial granulomas in the synovium do not always

demonstrate caseation. With appropriate staining, acid-fast organisms, fungi

and spirochetes (Lyme disease and secondary syphilis) can be demonstrated.

The presence of bacterial DNA in synovial biopsy samples can provide

important information in the diagnosis of infectious arthritis [15].

Occasionally, the diagnosis of chronic sarcoidosis is established after

synovial biopsy [16]. The characteristic histological feature is a

well-defined granuloma. The central area of the granuloma is occupied by

lymphocytes, which are predominantly CD4+, and by mononuclear phagocytes and

their progeny, including epithelioid cells and multinucleated giant cells.

Caseation is absent, but a small area of fibrinoid necrosis may be present.

The outer zone of the granuloma is formed by CD4+ and CD8+ lymphocytes,

fibroblasts, mast cells and other immunoregulatory cells.

Both gout and pseudogout can demonstrate tophus-like deposits in synovial

tissue [14]. When handling tissues, special care is required to preserve the

crystalline structures. Amyloid may be deposited in synovium in patients

with primary amyloidosis, Waldenstrom's macroglobulinemin, multiple myeloma

and adult cystic fibrosis [17]. Arthropathy associated with ochronosis and

haemachromatosis demonstrate characteristic histological features. Pigmented

villonodular synovitis, multicentric reticulohistiocytosis and rare tumours

of the synovial membrane require a biopsy for diagnosis.

Synovial biopsy can have a major role in the diagnosis of monarticular

arthritis. A closed needle biopsy of the knee joint might provide sufficient

tissue for histological, immunohistological and microbiological analysis. An

open biopsy or needle arthroscopic biopsy is the procedure of choice when

other joints are involved, and should be undertaken in the knee joint if

closed needle biopsy fails to yield a diagnosis.

Synovial biopsy in rheumatoid arthritis

The diagnosis of RA after the chronic polyarticular manifestations have

become established is usually based on characteristic clinical, radiological

and serological manifestations. Histological confirmation is not required.

The gross changes that are characteristic of RA result from chronic synovial

inflammation. Typically, the surface of the synovium becomes hypertrophic

and oedematous, with an intricate system of prominent villous fronds that

extend into the joint cavity. Microscopic evaluation of synovial tissue

inflammation in RA confirms marked cellular hyperplasia in the lining layer.

T cells, plasma cells, macrophages, B cells, neutrophils, mast cells,

natural killer cells and dendritic cells accumulate in the synovial

sublining layer (reviewed in [18]). The appearances are not specific for RA.

The dominant cell populations in the lining layer are fibroblast-like

synoviocytes and macrophages, which release an array of proinflammatory

cytokines and their inhibitors, promoting further intra-articular

perturbations. There is abundant production of matrix metalloproteinases

(MMPs), cysteine proteases and other tissue-degrading mediators, which

accumulate in the synovial fluid and augment joint damage by interacting

directly with exposed cartilage matrix. These features are present very

early in the disease course. T cells and plasma cells are prominent in the

synovial sublining layer. Perivascular T cell aggregates are observed in

50–60% of patients with RA. These aggregates can be surrounded by plasma

cells. There are two basic patterns of T cell infiltration. First,

perivascular lymphocyte aggregates can be found, which consist predominantly

of CD4+ cells in association with B cells, few CD8+ cells, and dendritic

cells. The second pattern of T cell infiltration is the diffuse infiltrate

of T cells scattered throughout the synovium. A subset of the CD4+ T cells

in synovial tissue is activated. A possible biological effect of activated

perivascular T cells in the synovium is the stimulation of migrating

macrophage populations through direct cell contact. This mechanism is known

to stimulate macrophage production of cytokines and MMPs in vitro. Many of

the synovial tissue T cells are, however, in a state of hyporesponsiveness.

Interdigitating dendritic cells, which are potent antigen-presenting cells,

are located in proximity to CD4+ T cells in the lymphocyte aggregates and

near the intimal lining layer. In addition, macrophages and lymphocytes

infiltrate the areas between the lymphocyte aggregates. The macrophages

often constitute the majority of inflammatory cells in the synovial

sublining layer. B cells constitute a small proportion of the total number

of lymphocytes in the synovial sublining layer. However, numerous plasma

cells may be present throughout the synovium, sometimes exceeding the number

of infiltrating T cells.

An issue that frequently arises in the context of possible associations

between synovial tissue immunohistology and progressive structural damage

relates to the acquisition of tissue samples from a knee joint and the

evaluation of radiographic images, usually of the hands and feet. Such

studies make the assumption that the immunohistological appearances in a

knee joint are representative of pathophysiological events occurring at

other sites. Evidence to support this hypothesis comes from a study of

patients with RA who underwent biopsy of a knee joint and a small upper-limb

joint on the same day [19]. Another important issue that requires

consideration is the question of selection bias. This issue has been

evaluated extensively, confirming that despite the degree of histological

variation within a joint, representative measures of inflammation can be

obtained by examining a limited area of tissue [20-23].

The intensity of the cellular infiltrate, the levels of activation and the

amount of secreted products vary greatly between individual patients with RA

and other arthropathies [20,24,25]. Many studies of synovial tissue have

been reported that indicate associations between immunohistological features

of inflammation and clinical measures of disease activity [20,26,27], as

well as with local measures of synovitis [28]. The immunohistological

measures of synovitis observed in the knee joint are reflected in other

joints from the same patient biopsied at the same time [19]. Clinically

uninvolved joints in patients with RA demonstrate similar immunohistological

changes, although less intensely than in the affected joints [29,30]. Serial

synovial biopsies in open therapeutic studies and in randomised clinical

trials showed that the immunohistological features of RA and other

arthropathies change after treatment with disease-modifying anti-rheumatic

drugs (DMARDs) [26,31-37], oral corticosteroids [38] and targeted biological

agents [39-42]. The mediators of inflammation that have been shown to change

in therapeutic studies include mononuclear cell populations

[26,31,32,35,36,39,40,42], adhesion molecule expression [35,36,38-40,42],

levels of cytokine production [31,33,35,36,41] and MMPs [34,36,37]. Thus,

synovial tissue analysis in patients with RA has revealed several surrogate

markers of disease activity and response to treatment.

Early rheumatoid arthritis

General comments

The approach to treating patients with early RA has changed substantially in

recent years. In most centres, early arthritis refers to patients who

present within 1 year of the onset of symptoms. This change has occurred for

several reasons. First, there has been a growing recognition that

irreversible structural damage can occur very early in the course of

inflammatory arthritis [49]. Second, the establishment of dedicated early

arthritis clinics facilitates the early referral of patients with

inflammatory arthritis [50]. Third, there is a wider recognition of reliable

diagnostic factors [51]. Fourth, rheumatologists have access to effective

therapeutic modalities that greatly reduce the rate of progressive joint

damage [52-54]. Last, it has been established that DMARD therapy reduces the

rate of progressive joint damage more effectively when introduced within 6

months of the onset of symptoms [55]. It is therefore now standard practice

to introduce conventional DMARDs, such as methotrexate, and even targeted

biological therapies, as first-line treatments in patients with RA [56].

The presence of some autoantibodies, including IgM-RF and

anti-citrulline-containing peptide (anti-CCP) antibody, facilitates an early

diagnosis of RA [57]. In addition, several clinical and laboratory factors

at baseline reliably predict outcome. These include higher baseline joint

counts, a high titre of IgM-RF, an elevated acute-phase response, the number

of baseline erosions and the shared epitope [58]. However, these factors

were identified in large cohorts and do not always apply to individual

patients. Some clinical investigators have developed algorithms that

incorporate selected prognostic factors to predict outcome [59,60].

The value of synovial biopsy

Studies of synovial tissue to identify indicators of outcome in RA, and

changes after treatment, have been necessarily limited in size in comparison

with similar studies that evaluated clinical and serum factors. Synovial

biopsy is an invasive procedure and, when performed at arthroscopy, is

technically complicated and expensive. Quantification of changes with

digital image analysis is also costly and requires considerable expertise.

However, the pathophysiological events occurring in tissue are more likely

than dispersed serum factors to reflect the clinical status and outcome in

individual patients.

Although there is no diagnostic role in early RA, synovial biopsy and tissue

analysis may provide important prognostic information. A few biopsy studies

have been reported that examined mediators of synovial tissue inflammation

and joint damage that were found to be associated with unfavourable clinical

and radiological outcomes (Table 2). In a limited longitudinal study of

patients with early inflammatory arthritis, and a mean disease duration of

9.6 months (range 2 weeks to 18 months), the number of synovial lining layer

macrophages at baseline was correlated with the number of new erosions on

radiographs of the hands and feet 1 year later (P = 0.002) [25]. Most

patients had RA. In all patients who developed new joint erosions it was

observed that more than 60% of the infiltrating lining layer cells were

macrophages, suggesting that a immunohistological analysis of synovial

tissue at baseline might identify individual patients who were at increased

risk of developing a more aggressive disease course. This observation is

similar to the findings in patients with established RA [27,43]. Macrophages

are the primary source of the proinflammatory cytokines IL-1 and TNF-á,

which induce the production of MMPs by fibroblast-like synoviocytes.

Employing in situ hybridisation techniques, it was observed that the number

of MMP-1-producing cells in the synovial lining layer, in contrast to cells

producing cathepsin B and cathepsin L, seemed to be strongly correlated with

the number of new erosions that developed during the first year of follow-up

(P = 0.0007) [25].

In a similar early synovitis cohort, the expression of MMP-2, MMP-9, MMP-14

and TIMP-2 (tissue inhibitor of metalloproteinases-2) was quantified in

synovial tissue biopsies obtained at baseline [61]. Radiographs of the hands

and feet were repeated after 1 year. The synovial tissue samples from

patients who developed joint erosions had significantly higher levels of

MMP-2 than those from the patients who did not develop erosions (P = 0.04).

There seemed to be considerable overlap between the groups, and the authors

did not distinguish between MMP-2 expression in the lining and sublining

layers. Nevertheless, the observation suggested that baseline tissue MMP-2

levels might be a marker for more aggressive synovial inflammation.

Early undifferentiated arthritis

General comments

With the emergence of convincing scientific evidence that very early

introduction of disease-modifying therapies inhibits progressive structural

damage more effectively [55], it is inevitable that some patients who

receive treatment will not meet the ACR criteria for RA and will have a

self-limiting, non-progressive arthritis. Thus, clinicians will seek a

balance between exploiting the early 'window of opportunity' in some

patients, and delaying effective treatment until the appearance of

sufficient diagnostic criteria in others. About 30% of patients have an

undifferentiated inflammatory arthritis at the time of their first

presentation to an early arthritis clinic [50]. Similarly, a diagnosis of RA

can be established in about 30% of patients. During the period of follow-up,

many of the patients with undifferentiated arthritis will develop features

that enable a diagnosis of RA, or other categories of arthritis. Several

factors have been identified that distinguish groups of patients with

undifferentiated arthritis who acquire a diagnosis of RA. Thus, the presence

in the serum of anti-perinuclear factor [62], anti-RA33 [63], anti-Sa [64],

anti-keratin [65], antifilaggrin [66] and anti-CCP antibodies [51] has been

associated with the diagnosis or outcome of RA. In addition, high-titre

antibody against serum amyloid A in patients attending an early arthritis

clinic with undifferentiated arthritis was associated with a subsequent

diagnosis of RA [67].

The value of synovial biopsy

Some studies employing synovial tissue analysis to identify early diagnostic

markers in patients with undifferentiated arthritis have been reported

(Table 3). In one study, a synovial biopsy was obtained from 95 patients who

presented with unclassified arthritis for less than 12 months [68]. The

objective was to determine which immunohistological markers could best

distinguish RA from other categories of arthritis. Using regression analytic

approaches, it was observed that high scores for CD38+ plasma cells and

CD22+ B cells were the best discriminating markers when comparing RA with

non-RA categories. The authors concluded that immunohistochemical analysis

of synovial tissue samples could be used to distinguish patients with RA

from other diagnostic categories.

In another study, immunohistological differences between RA and other

categories of arthritis were also observed in 71 patients, including 16 who

had had RA for less than 12 months [69]. The intensity of infiltration by

both T and B cells, and differential expression of á V integrin, seemed to

distinguish patients with RA from those with spondylarthritis and those with

osteoarthritis. The disease duration of RA did not influence the findings.

However, the immunohistological features highlighted in both of these

studies seem insufficiently disease-specific for routine use as diagnostic

markers.

The demonstration of intracellular citrullinated proteins in synovial tissue

samples from 18 of 36 patients with RA, and in none of 52 patients with

spondylarthritis, osteoarthritis and other categories of arthritis,

suggested a useful method of discriminating RA from other inflammatory joint

diseases [70]. This observation was the first description of a specific

histological marker for RA in synovial tissue. The specificity of

intracellular citrullinated proteins to RA is the subject of continuing

investigation, and it is clear that further biochemical characterisation of

the citrullinated proteins present in the synovium of patients with RA, and

other inflammatory joint diseases, is required [71,72]. Nevertheless, the

possibility that demonstrating intracellular citrullinated protein in

synovial tissue might be a new tool for the early diagnosis of

undifferentiated arthritis is an important prospect.

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