There is increasing evidence that aortic inflammation can occur in giant cell arteritis (GCA). This can result in the future development of aortic aneurysm, the rupture of which is life threatening. Experts debate whether or not routine screening for aortic arch involvement is warranted in patients with GCA.
Pro: Routine Imaging of the Aortic Arch Is Warranted in Giant Cell Arteritis: John Chen, MD, PhD, Kenneth Warrington, MD, James Garrity, MD
GCA is the most common form of vasculitis in the adult population, with an annual incidence of 19.8 per 100,000 individuals older than 50 years (1). Disease-related complications include vision loss from arteritic anterior or posterior ischemic optic neuropathy and central retinal artery occlusion. Because of its ocular manifestations, GCA is often diagnosed and managed by neuro-ophthalmologists. However, in addition to vision loss, GCA can have other vascular complications, including aortic aneurysm especially within the ascending thoracic aorta (2,3). Neuro-ophthalmologists may be less informed about the current guidelines of these systemic complications.
Involvement of the aorta from GCA is becoming increasingly recognized. Up to 66.7% of patients with GCA have evidence of aortitis on imaging (e.g., positron emission tomography [PET], computed tomographic angiography [CTA], and magnetic resonance angiography [MRA]) at diagnosis, and aortitis may lead to an increased risk of aortic aneurysm and dissection (3–6). Indeed, studies using PET-CT found that aortitis from GCA was associated with an increased risk of aortic dilation, structural damage, and aortic aneurysm (6,7). A recent meta-analysis found a 3-fold increased risk of thoracic aortic aneurysms and dissection compared with controls, with studies reporting these complications in 8.2%–33% of patients with GCA, depending on the length of follow-up (8–11). Aortic aneurysms are typically asymptomatic and, therefore, are often not discovered until the catastrophic event of dissection or rupture years after the initial diagnosis of GCA (3,9,11,12). If a thoracic aortic aneurysm ruptures, there is a 76% chance of death (13). In the 2 largest population-based studies, dissection/rupture ranged between 1% and 6% of patients with GCA (8,11,13), which resulted in a higher mortality in patients with aneurysm or dissection than other patients with GCA without aneurysm or dissection (14). These risks are highlighted by a population-based study of 96 patients with GCA, of which 11 had a thoracic aortic aneurysm, 6 of whom presented with acute aortic dissection leading to death (15). The risk of aortic aneurysm could conceivably be higher than that published in the literature because asymptomatic aortic aneurysms may go undiagnosed and subsequent deaths from aortic dissection may be incorrectly attributed to myocardial infarction. Surgical repair of an enlarging aneurysm could potentially be lifesaving (8,15).
Because of the increased risk of aortic aneurysm and mortality, the current American Cardiology guidelines recommend CT or MRI of the thoracic aorta at the initial evaluation of GCA (16). Despite this recommendation, these guidelines are rarely followed, especially if patients are diagnosed and managed by neuro-ophthalmologists or other providers not aware of the potential risks of aortic complications. At the Mayo Clinic, all patients with GCA are seen in conjunction with the rheumatology service which routinely screens all patients with cross-sectional imaging of the thorax, usually with chest CTA or MRA. If evidence of aortitis is detected, patients are surveyed with repeat imaging every 1–2 years to screen for progressive aortic dilatation. If aortic dilatation or aneurysm is found, patients are evaluated by vascular medicine and/or cardiovascular surgery for ongoing surveillance or intervention.
In our opinion, screening for this possible life-threatening complication is warranted. We routinely screen other diseases with a much higher cost-to-benefit ratio. For example, the American Academy of Ophthalmology (AAO) advocates yearly screening for hydroxychloroquine (Plaquenil) toxicity with multiple imaging and testing modalities for all patients exceeding 5 years of exposure because the risk of hydroxychloroquine toxicity reaches 1% at 5 years (17). Aortic aneurysm complications from GCA exceed this risk. If we are going to routinely screen for hydroxychloroquine toxicity, a condition that puts the retina at risk, it only makes sense that we should screen for aortic aneurysms that puts life at jeopardy.
Con: Neuro-Ophthalmologists Should Not Routinely Screen for Aortitis in Patients With Suspected Giant Cell Arteritis: Sashank Prasad, MD
Patients with GCA-related aortitis may face high morbidity and mortality from complications including dissection and aneurysmal rupture. Given that aortitis can have high-stakes clinical consequences, it is reasonable for clinicians to query whether to perform a screening diagnostic study to identify its asymptomatic presentation. Nevertheless, as I will argue, I believe that standard screening for aortitis is not indicated for most patients diagnosed with GCA by a neuro-ophthalmologist.
The estimated prevalence of aortic involvement in GCA based on clinical presentation is between 3% and 18%, but investigations using modern imaging studies (CT, MRI, and fluorodeoxyglucose [FDG] PET-CT) indicate that this may be a considerable underestimate of the true prevalence (3). Although many authors frequently try to highlight the role of imaging in the evaluation of patients with GCA, it is difficult to draw firm conclusions because the available literature consists mostly of small studies highly prone to selection bias. For example, 1 retrospective study showed CT evidence of aortitis in 48 patients with GCA; the prevalence of GCA could not be assessed, however, because fewer than half of the 351 GCA patients in the cohort were screened (18). Similarly, a case series emphasizing the utility of MRI to diagnose aortitis in patients with GCA reported on 6 cases, without controls (19). Finally, a retrospective study evaluating semiquantitative methods to analyze PET-CT concluded that the technique “has high sensitivity and specificity” for the diagnosis of aortitis in GCA; however, the study included 23 patients who had “a tentative diagnosis of GCA and suspected large-vessel involvement,” clearly demonstrating selection bias that prevents generalizability to the GCA population at large (20).
The issue of aortitis in GCA was addressed carefully by Mackie et al (8), who performed a meta-analysis after excluding studies judged to have high risk of selection bias. They tried to mitigate the effects of statistical heterogeneity inherent to small sample sizes using a random-effects model to estimate pooled prevalence. Their analysis rested mostly on 2 studies from large administrative databases, which suggested that patients with GCA may have a 3-fold increase in the risk of aortic aneurysm or dissection compared with the historical control rate in the general population. Given the paucity of adequate studies, however, they found that “the true relative risk and the time course of that risk remain unclear.”
More recently, using a nationwide database of coded diagnoses in the United Kingdom (UK), Robson et al (21)performed a retrospective multivariate analysis to assess the risk of aortic aneurysm in GCA. Almost 7,000 patients with GCA and over 40,000 matched controls were included. Adjusting for risk factors including the history of hypertension, hyperlipidemia, and tobacco use, their model showed that patients with GCA seem to have a 2-fold increase of aortic aneurysm. These authors noted that “a randomized controlled trial to demonstrate benefit of screening in patients with GCA would be the gold standard methodology of answering this research question”; however, no such trials exist, and on the basis of their current study, they concluded that “a separate screening program is not indicated.”
So, given the limitations of the available literature, what is the clinician to do? Does it make sense to obtain an imaging study to screen for asymptomatic aortitis in a patient suspected to have GCA? As with most challenges in medicine, there is unlikely to be 1 “black-and-white” answer that dependably addresses this question in all circumstances. Nevertheless, in trying to gauge whether screening may be helpful in general, there are several pertinent questions that should be addressed. For example, how secure is the diagnosis of GCA? Are clinical features of aortitis already manifest? Will the identification of subclinical aortitis affect either the acute or long-term treatment plan? As discussed in further detail below, there are several patient-related factors that influence the answers to these questions. Another way of looking at this is that there are also important physician-related factors to consider—a neuro-ophthalmologist's perspective on this issue will categorically differ from that of a rheumatologist or internist. To formulate a realistic answer to this question, it is pivotal to consider these differing clinical perspectives.
- How certain am I, based on clinical findings and other diagnostic data, that the diagnosis of GCA is correct? Will the identification of subclinical aortitis strengthen my diagnostic conviction? A neuro-ophthalmologist typically considers the diagnosis of GCA because a patient with particular demographic characteristics has presented with afferent and/or efferent visual symptoms. On the basis of the history and examination, we arrive at a pretest probability for the diagnosis, and then adjust that probability using data, such as serum inflammatory markers, imaging studies (often including fluorescein angiography and/or ultrasonography), and biopsy of the temporal artery. For a subgroup of patients, despite this clinical process, the probability of the diagnosis may remain difficult to gauge; an imaging study showing subclinical aortitis would, therefore, be of diagnostic value. The utility of an imaging study in this scenario, however, does not equate with its utility as a general diagnostic measure in all patients with suspected GCA—particularly when a neuro-ophthalmologist has already judged the probability of the diagnosis to be reasonably high.
- Are clinical features already evident to raise suspicion for aortitis? This seems obvious, but it is worth being explicit: while a neuro-ophthalmologist evaluates a patient with suspected GCA, if the patient describes dyspnea or chest pain, or the examination shows asymmetric pulses or: while limb ischemia, there is nothing to debate. Of course the patient needs an imaging study to diagnose aortitis or other large-vessel involvement. Preferably in the nearest emergency department! Thankfully, however, this situation is relatively rare. Importantly, it does not constitute an argument that screening for subclinical aortitis is indicated in all patients being evaluated with visual complications from possible GCA.
- If the suspicion of GCA is already reasonably high, and there is sufficient concern for severe complications including visual loss, isn't aggressive acute treatment already essentially compulsory? It is inevitable that a neuro-ophthalmologist sees a biased population of patients with a suspected diagnosis of GCA. With vision often threatened, the threshold to begin aggressive treatment is generally low. Regarding treatment of GCA-related aortitis, there are no consensus evidence-based guidelines, but the European League Against Rheumatism (EULAR) recommends high-dose corticosteroid (1 mg/kg/day of prednisone equivalent up to 60 mg/day) for 1 month followed by a gradual taper (22). This is no higher, and probably lower, than doses that would be used to treat most patients with visual compromise from suspected GCA (23). Therefore, for patients with suspected GCA being seen by a neuro-ophthalmologist, knowledge that the patient also has subclinical aortitis is unlikely to substantially affect acute treatment recommendations.
- Will the identification of subclinical aortic involvement affect the planned duration of treatment? Like acute therapy, long-term treatment decisions also are unlikely to be affected by the demonstration of subclinical aortitis for most patients with GCA who have presented with visual complications. During the slow taper of immunosuppressive treatment, clinical decisions to extend or augment treatment will be based on a careful history, examination, and serial testing of inflammatory markers. Among patients followed by a neuro-ophthalmologist through the acute phase of illness, there is no evidence demonstrating the added utility of thoracic imaging studies to guide long-term medical treatment.
- Will subclinical aortic involvement affect future surveillance for complications? Appropriate screening for thoracic aortic aneurysm remains a challenging issue both for the general population and for patients with GCA. Guidelines jointly issued by numerous societies (including the American Heart Association, American Stroke Association, American Association for Thoracic Surgery, and others) suggest that the initial evaluation of patients with GCA should include CT or MRI imaging of the chest (16). These recommendations, however, are rated Level “C,” meaning that their evidence base is limited to opinion rather than data from clinical trials. Moreover, the authors of these guidelines do not include rheumatologists or neuro-ophthalmologists, again demonstrating that the literature on this topic often has a biased perspective that limits its generalizability to all patients with GCA, or particular subgroups such as those presenting with visual complications.
In conclusion, aortitis can be an important complication of GCA, but for patients who present with visual complications, the available literature does not suggest that routine screening for subclinical aortitis aids in diagnosis or effective management. Furthermore, recommendations in favor of routine screening should account for its attendant risks, including radiation exposure and financial costs. Studies specifically addressing the utility of screening measures in the subgroup of GCA patients seen by neuro-ophthalmologists would be of considerable value.
Rebuttal: Drs. Chen, Warrington, and Garrity
Dr. Prasad provided many good points to further the discussion on the utility of screening for aortic disease in GCA.
One argument was that there are no prospective studies demonstrating the incidence of aortic involvement from GCA. Although this may be true, there are population-based retrospective studies demonstrating a real and significant risk of potential aortic complications, including aortic aneurysm rupture or dissection in up to 6% of patients with GCA (11). Other retrospective studies have shown that at 10 years of follow-up, the incidence of aortic aneurysms in patients with GCA can be as high as 33% (10). Early in the disease course of GCA, aortitis is frequent but is clinically silent and does not become symptomatic until the eventual catastrophic event of rupture or dissection. Detecting aortitis or structural damage early in the disease process is pivotal in preventing these potentially fatal complications.
Dr. Prasad quoted a nationwide database retrospective UK study, which found a 2-fold increase in aortic aneurysm. The current UK guidelines recommend chest radiographs to screen for aortic aneurysm in GCA (24), which only has a 60% sensitivity in detecting aneurysm (25). Therefore, the United Kingdom reported risk in this study is likely an underestimation of the true risk. Population-based studies have shown the risk of thoracic aortic aneurysm to be as high as a 17.3-fold increase in patients with GCA (9). Even if the increased risk is only 2-fold, the gravity of missing an aneurysm provides credence for routine imaging of the aorta in patients with GCA.
Although we agree with Dr. Prasad that the identification of aortitis does not alter the acute management or the planned duration of treatment, it does warrant increased surveillance for the formation of aortic aneurysm. Patients with an unrepaired thoracic aneurysm have been reported to have as high as an 80% 5-year mortality, which is influenced by aneurysm size (8,12,26). Because the lamina is disrupted, patients with an aortic aneurysm from GCA could conceivably progress faster than the rates of spontaneous aortic aneurysms.
Although we recommend imaging of the aorta in most cases of GCA, clinicians should take into account patient-related factors and consider whether detecting aortic damage would affect a patient's management. For example, if a patient has too many comorbid conditions to undergo aneurysm repair if present, screening may not be warranted (27). There are also downsides of imaging, including cost, radiation exposure, contrast allergy, and risk of finding “incidentalomas” such as lung nodules which often require serial imaging or even an invasive biopsy. Despite these drawbacks, we believe the risk of missing an aortic complication warrants imaging, provided the patient has no contraindications to potential aorta repair. Based on a recent meta-analysis, it has been proposed that only 5–10 patients with GCA would need aortic imaging to detect 1 previously unknown thoracic aortic aneurysm (8). This is a small number of patients required to screen to detect a potentially life-threatening condition.
For these reasons, at the Mayo Clinic, all patients with GCA are comanaged with rheumatology and screened for aortic involvement, which is something that clinicians should consider in following their patients with GCA.
Rebuttal: Dr. Prasad
There is no doubt, as Drs. Chen, Warrington, and Garrity point out, that aortic aneurysm and rupture can be an important complication of GCA. Routine screening would be quite welcome if, in fact, it leads to improved medical or surgical management that successfully reduced the incidence of these rare complications. At the same time, however, the medical field is fraught with examples where additional diagnostic testing does not always improve outcomes—just because we can know something does not mean that we should know it. Mammography and prostate-specific antigen screening, for example, are not uniformly valuable in all populations. In an era defined by a dizzying array of diagnostic investigations and spiraling health care costs, it is especially important to be judicious about ordering tests that demonstrate clear benefit. From that viewpoint, in my opinion, we should be skeptical about the acceptance of routine screening for aortitis in neuro-ophthalmic patients with GCA.
In arguing that most patients with GCA have imaging evidence of aortitis that portends an increased risk of aneurysm and dissection, Chen et al cite several articles that actually demonstrate the prevailing uncertainty around this clinical question. For example, the review by Bossert et al (3) concludes that “aortitis should be considered in patients with atypical clinical presentations of GCA, consisting, for instance, in isolated laboratory evidence of systemic inflammation or relapse during treatment” (3). Atypical presentations of this sort are not the type of clinical challenge routinely confronted by a neuro-ophthalmologist. Bossert et al go on to say, “to date, no evidence is available about the potential usefulness of PET or MRI in monitoring patients with GCA over time.” My review of the literature points to the same conclusion.
Several additional publications cited by Chen et al also suffer from inherent bias that renders them difficult to interpret. For example, the study by Blockmans et al included (6) “all patients with biopsy-proven GCA who ever underwent an FDG-PET scan;” because it is unclear how these patients were selected for evaluation, it is impossible to know how these results apply to all patients with GCA (i.e., ascertainment bias). Nevertheless, this intriguing study demonstrated that follow-up CT imaging shows increased aortic diameter that correlates with FDG uptake in the arch at the time of diagnosis. On average, however, this difference was on the order of 3 mm (40.4 ± 6.9 mm in patients with FDG uptake compared with 37.0 ± 2.8 mm in those without), but these diameters remain well below the threshold of 55–60 mm commonly used to select candidates for surgery (13). Studies such as this one demonstrate how screening measures with outcomes that reach statistical significance may not have tangible consequences when translated into the clinical arena.
Chen et al also cite the recent retrospective study by de Boysson et al (7), which is the largest series of patients with GCA evaluated with PET/CT imaging. Even this study illustrates the difficulty in determining whether screening for aortitis is a valuable proposition. Among 130 patients, “aortic complications” were subsequently detected in 9, but these findings lead to surgery in just 2 patients, one of whom died perioperatively. In my opinion, this study illustrates the difficulty in trying to demonstrate that screening has a positive impact on diagnosis, treatment, or outcome.
Certainly, this question remains a challenging dilemma, and I find it of great interest that the approach at the Mayo Clinic is to routinely obtain CT or MR imaging of the thoracic aorta in all patients with GCA. As Chen et al point out, this is the approach recommended by associations such as the American College of Cardiology. To date, however, the American College of Rheumatology has not published practice guidelines that endorse this recommendation, and anecdotal evidence suggests that there is no shortage of disagreement among rheumatologists on this issue. For example, at my institution, none of our practicing rheumatologists screen all patients for aortitis. This discrepancy among experienced rheumatologists highlights the controversies surrounding the issue, especially as it relates to the subgroup of patients with GCA likely to be under the care of a neuro-ophthalmologist.
Conclusion (by Andrew G. Lee, MD and Greg Van Stavern, MD)
Neuro-ophthalmologists should be aware of potential aortic arch involvement in all patients presenting with GCA. At this time, the decision to screen for aortic arch involvement (including the specific method of screening) should be made on a case-by-case basis. Situations which might warrant more aggressive screening would include worsening of inflammatory markers with no clinical evidence of relapse and symptoms of aortic ischemia.
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