�Department of Rheumatology, Hospital Universitario de Bellvitge-IDIBELL., Barcelona, Spain.†Department of Radiology, Hospital Universitario de Bellvitge-IDIBELL., Barcelona, Spain.
1These authors contributed equally to this article.The authors have no conflicts of interest to disclose.
Address reprint requests to: Francisco Javier Narváez García, MD, PhD, Department of Rheumatology (Planta 10-2) Hospital Universitario de Bellvitge Feixa Llarga, s/n.,
Rheumatoid arthritis (RA) and psoriatic arthritis(PsA) share a chronic progressive disease coursewith little or no chance for spontaneous regres-
ion. Structural damage is a feature of both RA and PsAnd reflects the spread of joint inflammation to cartilagend bone, resulting in progressive damage and irreversiblempairment of the joint function. These 2 conditionshare similar pathophysiological concepts and some, butot all, of the molecular players are identical. However,hey differ in the anatomical localization of inflammatoryesions. This is reflected by a different pattern of jointnvolvement in both diseases and also by differences in the
icroanatomical localization of inflammation within aingle joint (1-6). Current concepts of RA suggest it isrimarily a synovial disease. In consequence, structuralamage in RA is linked strongly to synovitis and is espe-ially prominent at the sites, where (1) the synovial mem-rane inserts into the juxtaarticular periosteum and (2)he insertion sites of collateral ligaments are located (1-3).n contrast, PsA is considered to be substantially differents it primarily affects the entheses (4-7). The enthesesonsist of fibrocartilage, which is a specialized tissue thatransduces mechanical signals from tendons to bone.
Enthesitis, which involves inflammation at sites whereendons, ligaments, or joint capsules attach to the bone, ishe hallmark of the spondyloarthropathies in general, andsA in particular, and is rarely seen in RA (4-6). Recentvidence has shown a close relationship between the sy-ovium and the enthesis within a joint, which has beenecognized as the synovio-entheseal complex (5). Enthesi-is can spread to the synovium and cause secondary syno-itis (4-7).
When PsA presents with symmetrical small joint poly-rthritis, it may be clinically indistinguishable from RA.n many cases, the presence of rheumatoid nodules, rheu-atoid factor or anti-cyclic citrullinated peptide (anti-CP) antibodies, or the findings of skin psoriasis, nail
hanges (onychodystrophy), involvement of distal inter-halangeal (DIP) joints, sausage toes or fingers, spinalnvolvement, or arthritis mutilans help to distinguish be-ween the 2 entities. However, although diagnosis is basedrimarily on clinical findings, it is sometimes difficultven for the trained rheumatologist to differentiate be-ween PsA and RA. This is especially true in some patientsith polyarthritis in whom the only clue to the diagnosisf PsA is a family history of psoriasis. The distinction isurther complicated by the fact that the joint symptoms ofsA may precede the onset of skin disease by many years8,9). In addition, up to 30% of RA patients test negativeor rheumatoid factor in serum; the prevalence of anti-CP positivity in seronegative RA does not exceed 23%f patients, and other pathognomonic features such asheumatoid nodules usually appear late in the disease pro-ess (10-13). Finally, radiographs are unhelpful in mostases, because many of the features used to distinguish
sA from RA (ie, juxtaarticular new bone formation, en- p
heseal and periarticular erosion, periostitis, and osteoly-is) do not occur in early disease (8-14).
Thus, in some patients with early arthritis, the differ-ntial diagnosis cannot be established unequivocally byonventional clinical, immunologic, and radiographic ex-minations. In this group of patients, additional methodshat support the clinical suspicion of early PsA or RA areequired. Magnetic resonance imaging (MRI) seems to beelpful in addressing this diagnostic problem. A few stud-
es of the small joints in the hand of patients with RA orsA have shown that inflammation is localized within the
oint capsule in RA; this is in contrast to PsA, wherextracapsular involvement is also present (15-19). On thisasis, it has been suggested that MRI could have a differ-ntial diagnostic value, although this issue has not beenefinitively established and has been scarcely evaluated inatients with early arthritis.The purpose of this small “proof of concept” study was
o perform a detailed analysis and compare typical MRIndings of the hand and wrist in patients with early PsAnd RA in whom radiographs were ambiguous, to inves-igate whether it is possible to differentiate between bothonditions in the early stages of the disease (duration ofymptoms �1 year) on the basis of MRI features.
ATERIALS AND METHODS
atient Recruitment and Selection Criteria
wenty early RA and 17 early PsA patients with symp-omatic involvement of the wrist and hand joints andnconclusive radiographs were studied prospectively withontrast-enhanced MRI.
The inclusion criteria were as follows: (1) age �18ears; (2) diagnosis of PsA according to the classificationriteria described by the CASPAR study group (20),here the diagnosis of RA was made according to the987 American College of Rheumatology classificationriteria (21); (3) duration of symptoms �6 weeks and12 months; and (4) no previous treatment, except non-
teroidal anti-inflammatory drugs or small doses or corti-osteroids (�7.5 mg/d of prednisone or equivalent).nly in 1 (6%) of the patients with early PsA did polyar-
hritis precede the appearance of psoriatic skin lesions.his patient presented seronegative oligoarthritis and PsAas suspected because of a family history of psoriasis.onths after the MRI, the patient presented the charac-
eristic skin lesions, which allowed confirmation of theiagnosis.Baseline radiographs of the hands and wrists were taken
or all patients. Results were interpreted by an experiencedadiologist (JAN) blinded to the clinical diagnosis. Nonef the included patients with RA had erosions at the onsetf the study. Twelve percent of patients with PsA hadone erosions as the sole abnormality; none had the typ-cal radiographic features of the disease (ie, juxtaarticularew bone formation, entheseal or periarticular erosions,
eriostitis, or osteolysis) at baseline.
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236 MRI features in early RA and PsA
Clinical Assessment
Baseline data were collected by the same rheumatologistand included age, sex, duration of symptoms, clinical pat-tern of joint involvement, acute phase reactants at thetime of the study (erythrocyte sedimentation rate andC-reactive protein), rheumatoid factor, anti-CCP anti-bodies, and HLA-B27. Radiographs of the hands andwrists were taken for all patients.
MRI Protocol and Analysis of MRI Images
MRI scans of the wrist (distal radius and ulna, carpalbones, and metacarpal bases 2-5) and fingers [metacarpalsproximal to bases, metacarpophalangeal (MCP) joints,proximal phalanges, proximal interphalangeal (PIP)joints, middle phalanges, DIP joints, and distal phalan-ges] of the dominant hand were obtained using a SiemensMagnetom Avanto 1.5 Tesla (T) scanner (Siemens, Er-langen, Germany) with a dedicated wrist coil.
The sequence of MRI study was as follows: (1) unen-hanced imaging of the fingers; (2) the patient was reposi-tioned so that the wrist was within the coil and unen-hanced imaging of the wrist was performed; (3) afterintravenous application of gadolinium diethylenetri-aminepentaacetic acid (GD-DTPA; 0.1 mmol/kg of bodyweight) using an magnetic resonance (MR)-compatibleinjector pump at a rate of 2.5 mL/s, enhanced imaging ofthe wrist was obtained; (4) the patient was repositioned sothat the fingers were within the coil and then enhancedimaging of the fingers was performed. The second Gd-enhanced image was acquired in �10 minutes after Gd-contrast injection.
The unenhanced study included coronal T1-weightedspin-echo (repetition time [TR] 408 ms, echo time [TE]21 ms, matrix: 224 � 320) and short tau inversion recov-ry (STIR) (TR 4000 ms, TE 29 ms, inversion time [TI]30 ms, matrix: 192 � 256) images, as well as turbopin-echo axial fat-suppressed T2-weighted (TR 4060s, TE 78 ms, matrix: 224 � 320) pulse sequences.The enhanced study included coronal fat-suppressed
1-weighted turbo spin-echo (TR 635 to 500 ms, TE 21s, matrix: 224 � 320) series. Additional axial fat-sup-
ressed T1-weighted turbo spin-echo (TR 635 to 500 ms,E 21 ms, matrix: 192 � 320) sequences were obtained
n 10 cases. The slice thickness was 3 mm without anyap, and the field of view was 11 to 13 cm in all the pulseequences obtained.
In accordance with the guidelines of our institutionalthics committee, formal approval for this study was notequired. The local ethics committee agreed that the find-ngs in this report were based on normal clinical practicend therefore were suitable for dissemination. All patientsave informed consent before the MRI study.
Two of the authors (JAN and JN; 18 years of experi-nce in musculoskeletal radiology and 16 years of experi-nce in reading MRIs, respectively) independently re-
iewed the MRIs. The patients’ identities were unknown. t
iscrepancies in findings were resolved in a subsequentoint review session and consensus was reached.
The presence or absence of synovitis, bone erosions,one marrow edema, enthesitis, tenosynovitis, periartic-lar soft-tissue edema, periostitis, and bone proliferationn each patient’s MRIs was registered. We used defini-ions included in the Rheumatoid Arthritis Magnetic Res-nance Imaging Scoring (22) and Psoriatic Arthritis Mag-etic Resonance Imaging Scoring (23-25) systems, whichere developed by the Outcome Measures in Rheumatol-gy Clinical Trials MRI group. None of these MRI fea-ures were scored.
Synovitis was defined as an area in the synovial com-artment showing intermediate- to low signal intensityn T1-weighted images, intermediate- to high signalntensity on fat-suppressed T2-weighted and STIR im-ges, and increased post-GD enhancement on T1-eighted MRIs of a thickness greater than the width of
he normal synovium. Bone erosion was defined as aharply marginated bone lesion, with typical signalharacteristics (on T1-weighted images, loss of normalow signal intensity of cortical bone, and loss of normaligh signal intensity of marrow fat), which is visible inplanes with a cortical break seen in at least 1 plane.one edema was identified as a lesion within the tra-ecular bone, with signal characteristics consistentith increased water content (low signal intensity on1-weighted images and high signal intensity on T2-eighted and STIR images) that shows contrast en-ancement, often with ill-defined margins. Accordingo its location, bone edema was also categorized aserientheseal, subchondral, or diaphyseal (23,24).Enthesitis was defined as diffuse bone marrow edema
djacent to the enthesis, as well as florid inflammatoryoft-tissue changes at this site.
Tenosynovitis was defined by the presence of signalharacteristics consistent with increased water contenthigh signal intensity on T2-weighted fat-saturated andTIR images, and low signal intensity on T1-weightedmages) or abnormal post-GD enhancement adjacent to aendon in an area with a tendon sheath.
Other features recorded were soft-tissue edema, perios-itis, and bone proliferation. Soft tissues were evaluatedor the presence of edema on T2-weighted images and forhe presence of hypervascularity on the images obtainedmmediately after contrast administration. Periostitis wasefined as low signal intensity thickened periosteum withronounced contrast enhancement compared with adja-ent bones. Bone proliferation was recorded in the case ofbnormal bone formation in the periarticular region, suchs at the entheses (enthesophytes were defined as the for-ation of bony spurs along the insertion sites of the en-
heses) and across the joint (ankylosis).MRIs of the same patients were presented randomly to
he reviewers and interpreted twice, with an interval of 7o 22 months between the 2 interpretations to determine
he intraobserver reliability.
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J. Narváez et al. 237
Statistical Analysis
Continuous data were described as mean � SD and cat-gorical variables were presented as percentages. Compar-sons between patient groups were made using the Stu-ent t test for independent continuous variables or theann–Whitney U test when the assumption of normality
Table 1 Clinical and Laboratory Characteristics ofPatients at Baseline
RA(n � 20)
PsA(n � 17) P
Age (yr) 48.7 � 11.2 45.3 � 11.6 0.38Women/men
(ratio)16/4 (4) 11/6 (1.8) 0.29
Disease duration(mean � SD)(mo)
7.5 � 4.1 8 � 4.29 0.93
ESR, mm/h 33 � 14 29.2 � 8.5 0.46CRP, mg/l
(referencevalue �5)
16 � 7 11.8 � 5.9 0.11
Nodules 0 (0%) 0 (0%)Rheumatoid
factor20 (100%) 0 (0%)
Anti-CCPantibodies
18 (90%) 0 (0%)
HLA-B27 0 (0%) 4 (23.5%)
Results are presented as mean � standard deviation (median fordisease duration) or number of cases with prevalence rates.
% of patients with involvement of MCP% of patients with involvement of PIP% of patients with involvement of DIP
Results are presented as number of cases with prevalence rates.DIP, distal interphalangeal; MCP, metacarpophalangeal; PIP,
rheumatoid arthritis.
was not achieved. To analyze categorical data, we per-formed the �2 test or Fisher’s exact test when the expectedvalues were less than 5. Statistical significance was definedas P � 0.05.
For the assessment of intraobserver reliability, kappastatistics were employed on all variables. Finally, for eachof the MRI features analyzed we also calculated sensitiv-ity, specificity, predictive positive value (PPV), and nega-tive predictive value (NPV) with 95% confidence inter-vals (95% CI), and accuracy [(true positive � truenegative)/(true positive � true negative � false positive �false negative)].
RESULTS
The baseline demographic and clinical characteristics ofthe 2 groups of patients are summarized in Table 1. Therewere no significant differences between the groups regard-ing mean age, male-to-female ratio, or disease duration.The groups also had a similar intensity of the initial sys-temic inflammatory response, as assessed by laboratoryparameters.
Table 2 shows the MRI findings in patients with PsAand RA and Table 3 shows the accuracy, sensitivity, spec-ificity, PPV, and NPV values for each of these features.
Some MRI features, such as the presence of enthesitisor extensive diaphyseal bone marrow edema, were ob-served exclusively in PsA (P � 0.0001). These distinctivefindings were present in 71% (12/17) of the patients withthis condition. Diffuse and, in some cases, pronouncedsoft-tissue edema spreading to the subcutis was also de-tected more frequently in patients with PsA (P � 0.002).
al interphalangeal; PsA, psoriatic arthritispsoriatic arthritis; RA,
PsA
RA(n �
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238 MRI features in early RA and PsA
There were no significant differences in the frequencyof synovitis, bone erosions, subchondral bone edema,or tenosynovitis between the 2 groups. However, in RAextensor tendons were involved more often than theflexor tendons, whereas in PsA the opposite was ob-served (P � 0.014). In addition, we also detected dif-ferences in the localization of bone marrow edema. Inpatients with PsA, it was found in the following sites:(1) adjacent to the enthesis, indicating enthesitis; (2)adjacent to cartilage in the subchondral bone; or (3) inthe diaphysis of the phalanges or the metacarpal bones,in some cases at a considerable distance from the sub-chondral bone and the capsular joint entheses and ex-tending down the shaft (Figs. 1-3). In patients withRA, bone marrow edema generally occurred adjacentto cartilage in the subchondral bone and was much lessextensive than in patients with PsA (Fig. 4). No cases ofperiostitis or bony proliferation, including enthesoph-ytes, were seen.
With respect to the discriminatory power of theMRI features examined, identification of enthesitis(accuracy � 0.86) and diaphyseal bone edema (accu-racy � 0.84) reliably differentiated PsA from RA (Ta-ble 3). The presence of these 2 features was 100%
Table 3 Sensitivity, Specificity, PPV, NPV, and Accuracy ofRheumatoid Arthritis
specific for PsA, but their sensitivity was only 71% and
65% for PsA and RA, respectively. These features alsoshowed a high PPV for PsA (100%), but only a mod-erate NPV (80% and 77%). The presence of soft-tissueedema and flexor tenosynovitis also achieved accuraciesgreater than 0.70 (0.75 and 0.702, respectively). Soft-tissue edema was highly specific for PsA (specificity95%, PPV 90%), but relatively insensitive (53%).Flexor tenosynovitis showed a sensitivity and specific-ity of 70% for PsA, with a high PPV (90%) but only amoderate NPV (70%). None of the other features an-alyzed achieved accuracies greater than 0.70, and themedian accuracy was 0.59. For PsA, the median sensi-tivity and specificity of the MRI findings were 0.67 and0.65, respectively.
For RA, the median sensitivity and specificity of theMRI features were 0.35 and 0.32, respectively, and themedian accuracy was only 0.40. The presence of exten-sor tenosynovitis showed the best discriminative powerfor RA, with a sensitivity and specificity �70%, a PPVof 74%, an NPV of 67%, and an accuracy of 0.70.Synovitis and bone erosions also showed high sensitiv-ity for RA (100% and 75%, respectively), but theirspecificity was low (12% and 24%). No other feature
showed sensitivity or specificity greater than 0.70 for
etacar
J. Narváez et al. 239
RA, and the presence of extensor tenosynovitis was theonly feature to achieve accuracy over 0.70.
In addition to the difference in the frequency of jointand bone abnormalities, patients with PsA and RA alsopresented significant differences in the articular distribu-tion of the abnormalities. The radiocarpal joint (P �0.0001), the midcarpal and carpometacarpal joints (P �0.014), and the MCP joints (P � 0.033) were affectedmore frequently in patients with RA, whereas the DIPjoints were affected only in patients with PsA (P �0.002). In the wrist, the most common sites for boneerosions were similar in the 2 diseases: the capitate, tri-quetrum, lunate, and scaphoid bones. In the MCP and
Figure 1 A 43-year old man with psoriatic arthritis. Plain rinterphalangeal joint. Coronal T1-weighted (left image) andmarrow edema in the third metacarpal (asterisks) withoutsoft-tissue edema adjacent to capsular insertions in the third pchanges in the STIR image near the capsular insertions (blackand joint capsular attachments (small arrows) at the third m
PIP joints, the most frequent location of bone erosions
was the second and third fingers (particularly on theirradial aspect) in RA and PsA.
The intraobserver reliabilities for bone erosions, syno-vitis, bone edema, enthesis, and tenosynovitis were kappa0.87, 0.88, 0.77, 0.71, and 0.81, respectively.
DISCUSSION
This study examined the capacity of high-field-strengthMRI to distinguish between RA and PsA in their earlystages. The high sensitivity of MRI for the detection ofearly inflammation and destructive joint changes, includ-ing the detection of bone marrow edema, makes this tech-
aph showed only soft-tissue swelling at the third proximalMR images showed extensive changes in diaphyseal boneteal thickening, as well as entheseal changes with diffuse
al interphalangeal joint (large white arrows). Note the edemas). There are marginal erosions adjacent to the ligamentouspal head.
adiogrSTIR
periosroximarrow
nique a potentially useful tool.
240 MRI features in early RA and PsA
Our results stress the potential of this imaging methodas a complementary approach for differential diagnosis inambiguous cases. We observed significant differences inMRI findings of the hand and wrist that can help differ-entiate PsA and RA, even in the early stages of disease. Wefound that some MRI features, mainly the presence ofenthesitis or diaphyseal bone edema and, to a lesser extent,the pattern of hand tendon involvement and the presenceof soft tissue edema, reliably differentiated PsA from RA(all these features achieved accuracies greater than 0.70).
In patients with PsA (Figs. 1-3), enthesitis was detectedas frequently as synovitis in MRI studies (16,26-30).Bone marrow edema may be subchondral as well as di-aphyseal and, in general, is more extensive than in RApatients. In fact, the presence of extensive diaphyseal bonemarrow edema in at least 1 phalanx or metacarpal bone, insome cases at a considerable distance from the subchon-dral bone and the capsular joint entheses extending down
Figure 2 A 38-year-old woman with psoriatic arthritis and n(C) and axial (D) contrast-enhanced fat-suppressed T1-weigmarked enhancement on (B) and (C) at the joint entheses admetacarpophalangeal joints, corresponding to enthesitis. Notextensive diaphyseal bone marrow edema changes, with ill-d(B) and (C) of the fifth metacarpal head, at a considerable diextending down the shaft (without periosteal thickening).
the shaft, is one of the most distinctive MRI features of
PsA (7,15-19,26-32). This observation has also beenmade in reactive arthritis, which is of interest because theradiographic characteristics of this condition are identicalto those of PsA (15). Flexor tendons are involved moreoften than extensor tendons in PsA (7,15-19,26-30).Diffuse and, in some cases, pronounced soft-tissueedema spreading to the subcutis is not uncommon inthis disease.
In contrast, in RA the signs of inflammation were lo-cated mainly in the synovial membrane and we did notfind evidence of enthesitis (Fig. 4). When present, bonemarrow edema generally occurred adjacent to cartilage inthe subchondral bone, alone or surrounding bone ero-sions, and was much less extensive than in patients withPsA. We found a greater involvement of extensor tendonsin RA than flexor tendons. In established RA, the oppositeis the case; however, consistent with our findings, someauthors have reported that extensor tendon involvement
radiographic appearance (A). Coronal STIR (B) and coronalMR images reveal high signal intensity changes on (A) andto joint capsule attachments (arrows) in the fourth and fifthecond and fifth finger flexor tenosynovitis (small arrows) and
high signal intensity on (A) and contrast enhancement onfrom the subchondral bone and the capsular joint entheses
ormalhtedjacente the sefined
stance
predominates in the early stages of the disease (33-35).
J. Narváez et al. 241
The MRI features with the best discriminative power,such as the presence of enthesitis or extensive diaphysealbone marrow edema, were present in approximately 71%of our PsA patients. This percentage is much higher thanthat found by Marzo Ortega et al. (17) in a similar com-parative study. Those authors examined only the secondto fifth MCP joints and found MRI-related enthesealchanges in no more than 30% of PsA patients. That re-port also confirmed that MRI has the capacity to detectenthesitis-associated pathology in the early stages of dis-ease, although the authors questioned whether thesechanges are sufficiently common to be of diagnostic use.The discrepancy in the percentages between the 2 studiescould be explained by the differences in the anatomicalarea studied. We conjecture that if the study is expandedto include the wrist (distal radius and ulna, carpal bones,and metacarpal bases 2-5) and fingers (metacarpals prox-imal to bases, MCP joints, proximal phalanges, PIPjoints, middle phalanges, DIP joints, distal phalanges),the probability of observing these distinctive findingswould increase and thus the diagnostic effectiveness
Figure 3 A 31-year-old man with psoriatic arthritis and normimages show diffuse, ill-defined signal intensity of the distalintensity on (B), corresponding to extensive diaphyseal boneof this hand obtained 3 years later (C) does not revealed evidlocated at the proximal joint surface.
would be improved.
Histopathological studies have suggested that the in-flamed synovial membrane of PsA differs in certain subtleways from rheumatoid synovium with less lining layerhyperplasia, more subsynovial edema, and a greater num-ber of synovial vessels per square millimeter (36). Theblood vessels in the synovium are tortuous and dilated inPsA, but straight in RA. Despite these differences in thehistopathologic features of inflamed synovial membranes,the morphologic findings and degree of synovitis identi-fied by static MRI in PsA and RA are indistinguishable(15-19). Synovial membrane activity can also be assessedby dynamic contrast-enhanced MRI (DCE MRI), a tech-nique that evaluates the time-dependent diffusion of gad-olinium in the inflamed synovium. Specifically, DCEMRI can measure the degree of neovascularization andvasodilation, which are both markers of inflammation ac-tivity, and can be quantified. Preliminary studies indicatethat this technique could be used diagnostically to differ-entiate RA from PsA. In the knee joint, DCE MRI hasshown a trend toward greater vascularity or inflammationin PsA than in RA (37). In the hand and wrist, the rate of
ographic findings. Coronal T1-weighted (A) and STIR (B) MRx (arrows), with low signal intensity on (A) and high signal
w edema. Note the absence of periosteal thickening. PA viewriostitis. There is a doubtful marginal erosion at the fifth PID,
al radiphalanmarroent pe
synovial enhancement following intravenous contrast in-
242 MRI features in early RA and PsA
jection does not differ between RA and PsA patients(matched for disease activity) in the early phases (duringthe first 3 minutes) (38,39). However, 15 minutes afterthe injection, the relative enhancement rate is statisticallyhigher in RA (39) and PsA exhibits a more abrupt fall incontrast-induced synovial signal intensity. The differencein synovial late enhancement between the conditions ap-pears to be related to the histologic differences in synovialvascularity mentioned above, which lead to more rapidwashout of the contrast medium.
Like RA, PsA is associated with substantial bone ero-sion. Current evidence indicates that radiological damageoccurs in the early stages of PsA (9,17,40). Our resultsshow that radiographic erosions are not uncommon evenin the early phases of PsA, being observed in 12% ofpatients with this condition. This percentage is similar tothat reported by Scarpa et al. (9) in a series of Italianpatients with early PsA (15%). In another study, Kane etal. (40) found that up to 47% of patients with early PsAdeveloped radiological erosions in the first 2 years even ifdisease-modifying antirheumatic drugs are administered.Some authors have suggested that bone erosions in PsAare probably less frequent than in RA (16), but our resultsdid not confirm this. In accordance with other studies(17,30), we did not find significant differences betweengroups in the frequency of bone erosions.
Differences in the localization of bone erosions withinthe joint between the 2 diseases have been reported. Ero-sions in RA are typically marginal and tend to occur in the“bare areas” (cartilaginous void) of the joint, where thesynovium is in direct contact with bone, as a result of
Figure 4 A 46-year-old woman with rheumatoid arthritis.contrast-enhanced fat-suppressed T1-weighted (C) MR imagisks), which show marked contrast enhancement, as well asynovium is in direct contact with bone. Note the areas ofbone marrow edema in fat-suppressed T2-weighted and cabsence of enthesitis changes.
synovial proliferation (2,3,33,41-44). By contrast, bone
erosions in PsA tend to occur adjacent to the collateralligamentous and joint capsular attachments (7,31,45). Inour experience, these differences are observed more fre-quently in the small joints of the hand, such as in theMCP, PIP, and DIP joints (Figs. 1-4). Recent studiesusing high-resolution microcomputed tomography forthe evaluation of bone architecture in MCP joints havedemonstrated other differences in periarticular bone le-sions between RA and PsA (46). Bone erosions in PsA aregenerally smaller and deeper than those found in RA andtheir shape is also substantially different: erosions in PsAare mostly �-shaped and tubule-shaped, whereas RAshows U-shaped erosions. In addition, in PsA they aremore evenly distributed and lack the strong preponder-ance for radial sites found in RA. Moreover, althoughosteophytes/enthesophytes in RA are rare and usuallysmall, they are highly prevalent, widespread, and moresevere in PsA, often affecting the entire circumference ofbone (creating the effect known as “bony corona”). Thereason for these differences is unclear. However, they maybe related to differences in the mechanisms of bone repairthat limit the size of erosions. Bone repair is more active inPsA than in RA. Thus, although RA bone repair resultsmainly in bone and cartilage resorption, in PsA it com-bines destructive elements with anabolic bone responses(47). This combination leads to the formation of entheso-phytes/osteophytes and to the development of periostitis.Schoellnast et al. (16) found that the presence of perios-titis, defined as thickened periosteum with pronouncedcontrast enhancement compared with adjacent bones,was an important discriminatory finding as it was ob-
al T1-weighted (A), fat-suppressed T2-weighted (B), andonstrating wrist and metacarpophalangeal synovitis (aster-
e erosions (large arrows) located at the bare areas, wherened signal intensity changes corresponding to subchondralt-enhanced fat-suppressed T1-weighted images. Note the
Corones dems bonill-defiontras
served in 68% of their PsA patients but was absent in their
J. Narváez et al. 243
RA cases. In our series of PsA patients, we did not observeany cases of periostitis or bony proliferation, includingenthesophytes. The discrepancy between the studies mayalso be due to the inclusion of distinct patient popula-tions, because periostitis does not usually develop in theearly stages of the disease (9,40,48).
A frequent and striking finding in our patients withPsA was the presence of extensive diaphyseal bone edema.It did not appear to correspond to incipient periostitis, asconcomitant low-signal thickened periosteum was notobserved on MRI. In addition, radiographs obtained atthe same time as MRI did not reveal signs of periostitis inany of these cases (Figs. 1-3), nor were signs seen in theradiological follow-ups over the next 3 years. However,because we do not have long-term radiological follow-up,we cannot rule out the possibility that these changes inbone marrow edema preceded the appearance of theperiostitis that was radiologically evident in later stages.Another hypothesis is that, as in RA, the bone edemacorresponds to regional osteitis. In RA, MRI bone edemaoccurs in 40% to 60% of patients and is strongly associ-ated with the development of bone erosion (49-51). InRA bone specimens resected in joint replacement surgery,osteitis has been observed where preoperative MRI scansshowed bone edema (52,53). These regions of bone in-flammation contain B and T lymphocytes, plasma cells,and macrophages closely apposed to osteoclasts. Compar-ative MRI/histologic studies of bone have not been per-formed in PsA, but Bollow and coworkers found someevidence of osteitis in subcortical bone in their biopsystudy of sacroiliac joints in patients with spondyloar-thropathies, including 2 with PsA (54). Unlike RA, thepresence of bone edema in patients with PsA has not beenshown to predict the appearance of erosions. However, arecent study showed that MRI bone edema in PsA corre-lates with radiographic joint damage scores (39). Hence,it was hypothesized that bone edema is a preerosive fea-ture in this disease. Further studies are needed to clarifythis point.
Finally, in addition to the difference in the frequency ofjoint and bone abnormalities, the articular distribution ofthese abnormalities also differed significantly between the2 conditions. The radiocarpal joint, the midcarpal joints,the carpometacarpal joints, and the MCP joints were sig-nificantly more frequently affected in patients with RAthan in patients with PsA, whereas, as is already known,the distal interphalangeal joints were only affected in PsApatients. These data corroborate previous reports (16).
Our study has several limitations that should be consid-ered when interpreting the results. First, the small sample sizeused to compare 2 distinct patient populations means thatthere is a high risk of Type II errors. Second, we includedonly symptomatic patients with “true” RA and PsA, and sowe do not know how frequently these changes are observedin patients with early, unclassified arthritis.
In conclusion, we observed significant differences in
MRI findings in the hand and wrist that can help to
distinguish between RA and PsA in the early stages ofdisease. MRI could be useful as a complementary tech-nique to assist in the differential diagnosis of selected pa-tients in whom diagnosis cannot be unequivocally estab-lished by conventional clinical, biochemical, andradiographic examinations. In these ambiguous cases, theidentification of certain MRI features, in particular en-thesitis or diaphyseal bone edema and, to a lesser extent,flexor tenosynovitis and extra-articular soft-tissue edema,strongly support the diagnosis of PsA. Further studies inlarger populations, including patients with early, unclas-sified arthritis, are needed to provide information to com-pare with our results and to confirm the potential appli-cation of MRI to improve diagnostic accuracy in early RAand PsA.
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