Department of Rheumatology and 1 Department of Magnetic Resonance Imaging (IDI), Hospital Universitari de Bellvitge IDIBELL, Hospitalet de LLobregat, Barcelona, Spain.
Correspondence to: J. Narváez, C/ Torrent de lOlla, no. 226 3° 1a, Barcelona 08012, Spain. E-mail: 31577edd{at}comb.es
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Abstract |
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Methods. Between 2000 and 2003, six patients with GCA and/or PMR seen in our department were diagnosed with aortitis using vascular MRI studies. In all cases, the study was performed according to a specifically designed protocol that included MRI and MR angiography (MRA).
Results. MRI was a hepful non-invasive method for diagnosis of aortitis in all cases, providing accurate information about its extent. In particular, MRI had a higher ability to detect earlier stages of vasculitis disclosing subclinical aortitis in five of the six patients. The main signs of early vascular inflammation observed were vessel wall thickness and oedema (six cases) and increased mural enhancement on postcontrast T1-weighted images (four cases). MRA disclosed lumen changes (stenosis) in two patients. On follow-up studies, whereas vascular stenosis and vessel wall thickness remained invariable, vascular wall oedema and contrast enhancement improved significantly when disease activity decreased.
Conclusion. MRI may be a useful technique for diagnosing patients with occult major artery involvement in GCA, whether presenting with classic symptoms of temporal arteritis or PMR. Its utility for monitoring the course of the disease and response to treatment requires further confirmation.
KEY WORDS: Polymyalgia rheumatica, Giant cell (temporal) arteritis, Aortitis, Magnetic resonance imaging
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Introduction |
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Because early diagnosis and treatment may impact morbidity and mortality substantially, current radiological research aims to increase the sensitivity of imaging techniques to early vascular inflammatory changes. Vessel wall thickness and oedema, as well as mural contrast enhancement, are features of vasculitis that are present early in disease, before lumen changes are apparent angiographically [610]. Recent investigations support the use of certain MRI sequences in the detection of these abnormalities, especially in the aorta and its proximal branches [610]. However, whereas the utility and limitations of MRI have been increasingly investigated in Takayasu arteritis [610], limited data are available regarding the usefulness of vascular MRI studies in GCA [1113]. Although sparse, these data are generally promising.
We here report our preliminary experience with this imaging technique in the study of the aorta and its proximal branches in patients with GCA and/or PMR, and review the scant data available in the literature.
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Material and methods |
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MRI technique
In all cases the protocol of study included electrocardiography- and respiratory-gated black blood T1- or proton density-weighted images, and black blood T2 fat-suppressed and/or STIR turbo spin echo images, obtaining transaxial sections from the pulmonary apex to the level of the diaphragm. Additionally, MR angiography (MRA) was performed using a contrast-enhanced three-dimensional spoiled gradient-recalled steady-state (SPGR) sequence oriented in either the coronal plane or oblique sagittal along the aortic long axis plane. After MRA acquisition, axial electrocardiography-gated T1-weighted spin-echo sequences were obtained in cases 2, 4, 5 and 6 in order to investigate mural contrast enhancement. The contrast agent used was gadolinium diethylamine triamine pentacetic acid.
This study has been approved by the ethical committee of our hospital. All patients signed an informed consent before the MRI study.
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Results |
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The main clinical and laboratory data of these patients are summarized in Table 1. Mean age at time of diagnosis for all patients was 74 ± 8 yr (mean ± S.D.). The mean disease duration before diagnosis of aortitis was 42 ± 25 months (3.5 ± 2 yr). Among patients with GCA, only in one case did the clinical features led to the diagnosis of aortitis (painful upper limb claudication in patient 1); in the remaining cases, the possibility of subclinical aortitis was considered as part of the differential diagnosis of patients who were in apparent clinical remission and who had unexplained persistence of raised acute-phase reactants. In the two patients originally diagnosed with PMR, the possibility of underlying occult vasculitis was explored as a cause of failure to respond to habitual doses of CS (despite the favourable initial response, both patients presented persistence of raised laboratory inflammatory markers during follow-up and frequent relapses in the setting of tapering prednisone dosage); this fact has been previously documented in a similar case [16]. In one of these patients, a temporal artery biopsy (TAB) was performed after the detection of abnormalities on MRI/MRA, and was negative; the other refused the biopsy. Of interest, only in one of the six patients with evidence of aortitis on MRI did the chest radiograph showed aortic abnormalities suggesting this complication.
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Discussion |
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Thus, aortitis is of concern because it is a relatively frequent complication of GCA that carries a risk of fatal dissection or rupture. Furthermore, this complication is often difficult to recognize in the early stages because of its indolent course in most patients and the poor specificity of the symptoms and physical examination. In this clinical scenario, non-invasive methods are frequently requested in GCA to confirm ongoing vasculitis, to monitor its course and to disclose subclinical inflammation during apparent clinical remission.
Is MRI potentially useful in these issues? Although based on small number of patients, our experience suggests that MRI may be a useful technique for the detection of vasculitis in cases with involvement of the aorta and its proximal branches, providing accurate information about its extent and intensity. In particular, MRI has a higher ability to detect earlier stages of vasculitis, disclosing, as in our patients, subclinical aortitis. These cases illustrate that occult aortitis should be considered in patients with GCA in apparent clinical remission and unexplained persistence of raised acute-phase reactants. Like conventional angiography, MRI provides detailed lumen information with high sensitivity and specificity for detection of stenosis, occlusions, dilatations and aneurysms [18, 19]. Imaging data are obtained non-invasively in a multitude of planes, avoiding the risks of arterial puncture, iodinated contrast load and radiation exposure. Moreover, in contrast to conventional angiography, MRI also provides complementary information about vessel wall thickness, oedema and mural contrast enhancement. These abnormalities seem to represent the early vascular inflammation that precedes the development of lumen changes [610]. Their detection can be of great clinical value, since it is assumable that early diagnosis and prompt treatment may prevent mortality and improve morbidity substantially. It is likely that most, if not all, patients with GCA have aortic inflammation at some point [5, 20]. Persistent aortitis may increase the risk of aortic dissection and rupture even in the absence of an aortic aneurysm. Assessment for persistent aortitis should then go beyond that for possible aneurysm only, and should include assessment for possible inflammatory wall changes.
The value of these paremeters in the diagnosis and assessment of disease activity has been explored in Takayasu arteritis. Vessel wall thickening, which can also be assessed by computed tomography (CT), is thought to be caused by inflammatory tissue proliferation [610]. The presence of a thickened aortic wall confirms the ongoing vasculitis, although this finding alone cannot distinguish active inflammation from chronic fibrotic lesions [6, 810]. Identification of vessel wall oedema on certain MRI pulse sequences (mainly STIR and fat-suppressed T2-weighted sequences) seems to be a parameter potentially important in monitoring response to therapy [610]. However, a recent study by Tso and collagues [7] has cast doubt on the reliability of this parameter as a measure of disease activity. Increased mural enhancement on postcontrast T1-weighted images reflects increased vascularity and/or excessive leakage of contrast out of the vasa vasorum, although histopathological correlation is not currently available [6, 8, 9]. There are some studies demonstrating a positive correlation between raised acute-phase reactants and increased vessel wall enhancement [8, 9], which is the best of these parameters to evaluate the disease activity. In general, active inflammation is assumed to be present if vessel wall enhancement is equal to or greater than the myocardial tissue signal [8, 9]. In our series, all patients with evidence of vessel wall thickness and oedema presented raised acute-phase reactants. In four of these patients, postcontrast T1-weighted images were obtained, and in all cases the thickened arterial wall showed increased contrast enhancement. Of interest, as suggested by the improvement of the vascular wall oedema and contrast enhancement in our patients, it would seem that the MRI results coincide with disease activity, although this finding requires further confirmation.
Available data on the evaluation of vascular MRI studies in GCA is sparse. There are some additional data supporting the usefulness of MRI in the diagnosis of aortitis in GCA, including one series of 14 patients with early GCA and aortitis studied with MRI and 18-fluorodeoxyglucose positron emission tomography (18-FDG PET) [1113]. As in GCA, few reports have been devoted to exploration of the role of vascular MRI studies in PMR. Marzo-Ortega et al. reported the case of a patient with PMR which was difficult to treat with low doses of CS and was found to have underlying vasculitis involving the brachial artery on an MRI study of the shoulder, a finding which can explain the requirement for higher doses of steroids [16]. This report led us to investigate the possibility of an underlying vasculitis in two similar patients with PMR; in both cases the MRI/MRA study disclosed subclinical aortitis. These observations highlight the close link between PMR and GCA, and clearly illustrate that failure to respond to habitual doses of CS in PMR may reflect an underlying vasculitic process that may require higher doses of steroid treatment. This vasculitis process can be detected non-invasively by MRI or 18-FDG PET [11, 20], especially outside the classically recognized temporal artery distribution. Its identification helps in decisions about treatment. In fact, we cannot discard the possibility these patients had classic GCA, although the extent of the vasculitis was not detected at diagnosis (in none of them was a TAB initially performed). Thus, about 10% of patients originally presenting with isolated PMR have vasculitis on histological examination, requiring a change in diagnosis to GCA [1]. Moreover, some investigators have suggested that GCA may take on a large-vessel form associated with PMR, with a low frequency of temporal artery involvement (this could explain the negativity of the TAB performed after the detection of abnormalities on MRI/MRA) [21].
Both helical CT with contrast enhancement [22] and 18-FDG PET [11, 20] are surfacing as viable alternatives to MRI in the study of aortitis in GCA. Advantages of MRI over CT include safer contrast media with no nephrotoxicity, no ionizing radiation, and multiple acquisition planes, as well as increased sensitivity in the detection of oedema. Whole-body 18-FDG PET can identify vascular lesions that are not detected using MRI and seems to be more reliable than MRI in monitoring disease activity [11, 20], but currently this is still a research tool and needs to be further validated in prospective studies.
In conclusion, although based on a small number of patients, there is some evidence to suggest that MRI may be a useful technique for diagnosing patients with occult major artery involvement in GCA, whether presenting with classic symptoms of temporal arteritis or PMR. Its utility for monitoring the course of the disease and response to treatment remains to be determined. Although sparse, our preliminary experience in this issue is promising, but this question should be further examined in appropriately designed studies.
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The authors have declared no conflicts of interest.
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References |
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