Large-Vessel Vasculitis in Ophthalmology: Giant Cell Arteritis and Takayasu Arteritis

Abstract

Giant cell arteritis and Takayasu arteritis are large-vessel vasculitides that share multiple common features but also have significant differences in epidemiology, demographics, clinical presentation, evaluation, and treatment. Giant cell arteritis is more common in elderly patients of Caucasian descent versus Takayasu arteritis, which is more prevalent in younger patients of Asian descent. Although traditionally age has been the main criterion for differentiating the 2 etiologies, modifications in the diagnostic criteria have recognized the overlap between the 2 conditions. In this monograph, we review the diagnostic criteria for both conditions and describe the epidemiology, pathogenesis, histology, evaluation, and management for large-vessel vasculitis in ophthalmology. Additionally, we describe ocular imaging techniques that may be utilized by ophthalmologists to identify manifestations of large-vessel vasculiti- des in patients. Lastly, we compare and contrast the key clinical, laboratory, and pathologic features that might help ophthalmologists to differentiate the 2 entities.

Vasculitides are autoimmune diseases that result in the inflammation of blood vessels. The classical classification of vasculitides is by size of the affected vessel: large-vessel, medium-vessel, and small-vessel vasculitis. Large-vessel vascu- litides (LVV) are defined as those that affect the aorta and its major branches.¹ The walls of these larger vessels consist of 3 layers: an outermost layer (tunica adventitia), middle layer (tunica media), and inner layer (tunica intima). In addition, due to their relatively thicker walls, these large-vessels have an intrinsic vasculature called the vasa vasorum.² The 2 major forms of Lvv are Takayasu arteritis (TKA) and giant cell arteritis (GCA).³ While both TKA and GCA are LVV, they have several subtle distinctions in their histopathology and the different ways they affect the layers of large vessels can be detected by ocular imaging techniques. As such, they are recognized as separate diseases that differ in their pathogenesis, epidemiology, demographics, symptomatology, and pharmacological treatment.

IMMUNOLOGIC MECHANISMS AND PATHOGENESIS

TKA Immunopathology

Although both GCA and TKA are LVV that can affect the same blood vessels, GCA also affects the superficial temporal artery and thus GCA has a target site for obtaining histopathologic confirmation of the diagnosis. In contrast, TKA mainly affects the aorta and its immediate major branches and tissue biopsy is difficult if not impossible in most cases of TKA.

Animal models for TKA are limited by the lesser thickness of their vessel walls (which correlate to the animal's size) and thus are not directly analogous to human LVV.¹ The pathogenesis of TKA is believed to occur in 2 phases: an acute phase characterized by lymphocytes and multinucleated giant cells infiltrating the adventitia, and a chronic phase characterized by fibrosis of the adventitia and intima and potential atherosclerotic plaque forma- tion.⁴ During the acute phase of TKA, CD4+ T cells infiltrate the otherwise immune-privileged vessel wall followed by activation of dendritic cells and T cells and subsequent LVV. It is believed that aortic tissue in TKA expresses the 65 kDa heat-shock protein following some form of triggering stress response.⁵ Once this heat-shock protein is expressed, vascular cells express major histocompatibility class I chain-related A (MICA),⁶ and then T cells and natural killer (NK) cells recognize MICA on these vascular cells and release perforins.⁷ This corresponds with an acute vascular inflammation and the release of proinflammatory cytokines,⁵ which attract mononuclear cells and T cells to infiltrate the vessel wall producing LVV.⁸

In addition, vascular dendritic cells are activated after their Toll-like receptors (TLRs) bind to their specific ligand.⁹ Usually pathogen-associated molecular patterns (PAMPs) serve as ligands for TLRs, but the precise mechanism for ligand activation in vascular dendritic cells in TKA remains ill-defined.⁵ Th1 cells then infiltrate the vascular wall and recognize epitopes of the “antigen” presented on the dendritic cell MHC leading to release of interferon-gamma (IFN-γ). This IFN-γ, in turn, activates nearby macrophages leading to granuloma formation.⁸ The proinflammatory effect of these Th1 cells is strengthened by the secretion of IL-17 from Th17 cells–this cytokine serves as a powerful neutrophil chemotactant, thus mobilizing neutrophils to the vascular wall and producing LVV.

GCA Immunopathology

Similar to TKA, the pathogenesis of GCA involves vascular dendritic cells in the adventitia of large vessels being activated by an unknown immunologic trigger. In GCA and TKA the large vessels are affected, but GCA also affects the temporal artery. Vascular dendritic cells release chemokines that recruit CD4+ T cells to the vessel wall via the vasa vasorum.² Upon their arrival to the adventitia, the dendritic cells serve as antigen-presenting cells that induce these CD4+ T cells to become Th1 cells, Th17 cells, or T regulatory cells.^2,10 As in TKA, Th1 cells recruit macrophages that are involved in granuloma production, but other subsets of CD4+ T cells also induce macrophages in GCA.

In response to IL-17 from Th17 cells, macrophages in the adventitia in GCA recruit other inflammatory cells and induce the synthesis of additional inflammatory mediators (eg, IL-1beta and IL-6).^1,2,10 Th1 cells release IFN-γ and induce macrophages in the tunica media leading to granuloma formation in GCA. These macrophages synthesize matrix metalloproteases and produce reactive oxygen species, which degrade surrounding connective tissue (eg, the internal elastic lamina) in GCA.^1,2,11 Macrophages at the intima-media border produce growth factors (eg, vascular endothelial growth factor, fibroblast growth factor and platelet-derived growth factor) that result in myofibroblast proliferation, thickening of the tunica intima,² and proliferation of the vasa vasorum into the tunicae media and intima in GCA.⁴

Comparison of the Pathogeneses of TKA and GCA

While the pathogenic and immunologic mechanisms of GCA and TKA are remarkably similar, the specific mechanisms are not identical. Heat-shock proteins are not believed to be involved in the pathogenesis of GCA. In TKA, the interaction between MICA and gamma-delta T cells/NK cells plays an essential role in the pathogenesis of the disease including chemotaxis of CD4+ T cells to the vessel wall. In GCA, however, vascular dendritic cells release chemokines that attract CD4+ T cells to the otherwise immune-privileged vessel wall. Additionally, while both processes rely on Th1 cells and Th17 cells, the extent of their roles in the pathogenesis of each disease may vary extensively. For example, patients with GCA who are administered glucocorticoids demonstrate a sharp decrease in Th17 cells and a respective decrease in systemic inflammatory features, but show no change in Th1 response levels. This led to the hypothesis that the Th17 pathway is involved with the acute onset of GCA, while Th1 pathway is responsible for the chronicity and relapsing nature of GCA.¹² Interestingly, experiments by Saadoun et al showed that Th1 levels drop in response to glucocorticoid administration in patients with TKA.⁸

Although both TKA and GCA respond to treatment with glucocorticoids, further elucidation of the specific immunologic differences in TKA and GCA may lead to more targeted immunotherapies based upon the different type and roles of inflammatory cytokines in these 2 LVV.

HISTOPATHOLOGY

TKA Histopathology

The characteristic feature of TKA on histology is a dense fibrosis around the large-vessel tunica intima and/or adventitia, which causes the aorta to become thick and rigid. The aortic lumen has alternating areas of narrowing, which can be separated by aneurysms or normal-sized lumens. Such stenoses are most commonly located distal to the left subclavian artery. Both acute inflammatory and fibrotic lesions can be found within the same vessel in TKA. “Acute phase” lesions have different components based on the layer of the vessel wall. The inflammatory infiltrate of the tunica adventitia consists of lymphocytes and plasma cells. The tunica media infiltrate in TKA includes lymphocytes, plasma cells, and giant cells, as well as neovascularization. The thick tunica intima in TKA demonstrates ground substance, mucopolysaccharides, smooth muscle cells, and fibroblasts.⁴

GCA Histopathology

In contrast to TKA, the adventitia is less commonly affected in GCA. Instead, there is prominent inflammation of the tunica intima and inner tunica media. These are relatively acellular areas that can calcify and trigger a “foreign body-like” inflammatory reaction in GCA with granulomas forming around areas of atrophic tissue.¹³ These lesions are not necessarily continuous and thus can produce “skip lesions.” The main inflammatory process involves the internal elastic lamina (IEL) in GCA. In biopsy-proven GCA, the IEL is often fragmented and the destruction of the IEL may allow the free flow of inflammatory cells in both the tunica intima and the inner layer of the tunica media in GCA.⁴

Comparison of TKA and GCA Histology

Although the histopathological features of TKA can be similar to GCA, subtle clues may distinguish the 2 disorders. TKA is more likely to involve the adventitia than GCA, whereas GCA is more likely to show features of neovascularization in the tunica media. These findings suggest that GCA and TKA are likely different forms of LVV.

EPIDEMIOLOGY

GCA and TKA differ widely in their epidemiology and associated symptoms and signs. GCA is the most common systemic vasculitis in Western countries and is primarily a disease of the elderly. GCA typically occurs in individuals over the age of 50 years with a peak incidence occurring in patients over 70 years of age.⁴ GCA is more prevalent amongst women than men, and is mostly reported in patients of Northern European ancestry, particularly those of Scandinavian descent.¹⁴ In contrast, TKA differs from GCA in that it is predominantly seen in young women with an age of onset before age 40 years. TKA is most commonly reported in women of Asian rather than European descent.¹⁵ Interestingly, recent research from China has indicated that it is difficult to distinguish the presentation of GCA from TKA in case series reports, thus emphasizing the fact that physicians in the Asia-Pacific region should perform comprehensive clinical exams for patients that present with symptoms suspicious of either of these diseases.¹⁶

GCA is commonly associated with polymyalgia rheumatica (ie, aching and morning stiffness in the proximal shoulder and hip girdles). TKA, on the other hand, commonly leads to renovascular hypertension, aortic regurgitation, or left ventricular hypertrophy, which are not common features of GCA.¹⁷ Currently, no ocular risk factors have been identified that either 1) increase the incidence of GCA or TKA, or 2) exacerbate the likelihood of ocular disease manifestations. Rather, studies have found associations between gender,¹⁸ age,¹⁹ and underlying history of diabetes or atherosclerosis²⁰ and onset of ocular manifestations (including permanent vision loss) in GCA.

DIAGNOSTIC CRITERIA IN GCA AND TKA

GCA Signs and Symptoms

Ocular symptoms and signs that may point clinicians towards GCA include both permanent and transient vision loss as well as diplopia.²¹ Additionally, pallid disc edema, combined retinal, choroidal and optic nerve ischemia, and double vision/ophthal- moplegia may be seen. Cranial symptoms of GCA include jaw claudication, temporal headache, and scalp tenderness. Systemic symptoms include malaise, limb claudication, anorexia, weight loss, fever, polymyalgia rheumatica, and other constitutional systems (eg, night sweats, malaise, arthralgia, etc).²² Less common symptoms in GCA include peripheral neuropathies, tongue necrosis, scalp necrosis, stroke, etc.^21,23–25 A full ophthalmologic examination is recommended for most patients with GCA, including visual acuity, visual field, pupillary, and fundus examinations.²⁶

The American College of Rheumatology (ACR) criteria for the classification of GCA includes²⁷:

• 1. Patient age >50 years old
• 2. New-onset headache
• 3. Abnormalities of the temporal artery (eg, tenderness, nodularity, or decreased pulsation)
• 4. Erythrocyte sedimentation rate (ESR) >50 mm/h
• 5. Abnormal temporal artery biopsy (TAB)

The 1990 ACR criteria yield a high sensitivity of 93.5% and a high specificity of 91.2%.²⁷ However, it is not without its setbacks as cases of ophthalmic GCA may be missed.²⁸ Firstly, it does not account for the various degrees of association that each of these criteria has with GCA diagnosis. Secondly, it would be ideal to have access to a framework that does not predicate screening for GCA via TAB. A diagnostic tool utilizing a neural network model based solely on GCA signs and symptoms created by Ing et al in 2019 helps address these limitations.²⁹ Such tools allow clinicians to identify those patients for whom they should have a high index of suspicion of a GCA diagnosis and order a confirmatory TAB. The diagnosis of GCA is best confirmed by a positive biopsy, although some rheumatology societies advocate ultrasound.²⁹

Diagnostic Procedures in GCA

Temporal artery biopsy (TAB) is considered the benchmark method of diagnosing GCA. Pathological examination of affected vessels usually reveals a fragmented internal elastic lamina, with a cellular infiltrate extending transmurally.³⁰ Multinucleated giant cells are not necessary for diagnosis of GCA.³⁰ In the meta-analysis, Rubenstein et al identified that the sensitivity of TAB is 77.3%, making it a viable diagnostic approach for GCA.³¹ Furthermore, an abnormal TAB, as well as other signs and symptoms of GCA, are included in the 1990 ACR criteria; thus, this inclusivity in the ACR criteria yields a higher sensitivity and specificity compared to TAB alone. However, a negative TAB does not necessarily rule out GCA.

A potential alternative to TAB is temporal artery ultra- sound.^32–34 While temporal artery ultrasound is somewhat controversial in diagnosing GCA, multiple studies support the potential use of ultrasound to assess the risk of GCA at the bed-side.^32–34 In 2018, Schmidt identified 4 pathologic findings of GCA when using the color Doppler ultrasound (CDUS) in GCA³²:

• 1. “Halo sign” (ie, hypoechoic wall thickening in the temporal artery)
• 2. “Compression sign” (ie, noncompressible arteries)
• 3. Stenosis
• 4. Vessel occlusion

Schmidt reported a sensitivity of 77% and specificity of 96% for temporal artery ultrasound with a positive and negative likelihood ratio of 19 and 0.2, respectively.³² These parameters illuminate that temporal artery ultrasound may provide appreciable diagnostic value in assessing risk for GCA.

Computed tomography (CT), computed tomography angiography (CTA), magnetic resonance imaging (MRI), and magnetic resonance angiography (MRA) may also offer utility in diagnosing GCA. CT/CTA and MRI/MRA may show signs consistent with GCA including arterial wall thickening, aortic ectasia, stenosis of aortic branches, and contrast uptake in inflamed vessels.³⁵

The use of ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) has been of increasing interest in GCA and vasculitis overall. In ¹⁸F-FDG PET, deoxyglucose can be taken up by metabolically active cells. Increased concentration of deoxyglucose can indicate arteritis and signify GCA; moreover, the exact concentration may depict disease severity.^35,36 Combined use of ¹⁸F-FDG PET and CT scanners have been becoming more popular.^35,3618F-FDG PET/CT allows for more exact localization of metabolically active and thereby increased sensitivity.³⁵

Ocular Imaging Techniques to Identify GCA

There have been increasing efforts to utilize ocular imaging techniques to help diagnose GCA; optical coherence tomography (OCT) is a specific one of interest. A preliminary study by Maldiney et al evaluated the utility of full-field OCT (FFOCT) in diagnosing GCA by analyzing the TAB specimens. FFOCT uses face whitelight interference microscopy to obtain high-quality visualization of biological structures and the subcellular metabolic contrast in tissue depth.³⁷ FFOCT also allows for rapid and onsite acquisition ofTAB specimens, even within minutes.³⁷ They found that FFOCT offers spatial resolution with high enough quality to gather quantitative information on the thickness of artery wall layers and the architecture of the connective tissue.³⁷ Moreover, they ascertained that FFOCT imaging results correlated to those of traditional histology methods when analyzing TAB specimens.³⁷ Maldiney et al ultimately concluded that FFOCT offers potential in distinguishing the architectural changes in arterial walls that occur in the inflammatory process of GCA.

OCT angiography (OCTA) is another ocular imaging method that may offer potential in diagnosing GCA. In eyes that had arteritic anterior ischemic optic neuropathy (AAION), OCTA was able to discern superficial peripapillary capillary dilation that was consistent with acute vascular changes in AAION.³⁸ OCTA was able to ascertain other changes (eg, retinal capillary perfusion defects) that corresponded with vision loss.³⁸ Follow-up OCTA revealed superficial peripapillary capillary attenuation that was consistent with vision loss.³⁸

Other studies have shown the use of OCT in rare presentations of GCA. For example, in a case of GCA with bilateral corneal edema, Tran et al demonstrated the use of swept-source OCTA (SSOCTA) in identifying choroidal infarction consistent with GCA.³⁹ It is worthwhile to re-emphasize at this point that while these ocular imaging findings may help ophthalmologists to screen for patients with GCA, the only way to conclusively make a diagnosis of GCA in a patient is with a TAB.

TKA Signs and Symptoms

Unlike GCA, the diagnosis of TKA can be made clinically and with diagnostic imaging—a biopsy is not required. The ACR criteria for the diagnosis of TKA in 1990 include⁴⁰:

• 1. Age at disease onset is ≤40 years old
• 2. Limb claudication
• 3. Decreased brachial artery pressure
• 4. >10 mm Hg difference in blood pressure between arms
• 5. Aortic or subclavian artery bruit(s)
• 6. Arteriogram abnormality

While the ACR included age as one of its diagnostic criteria for TKA, Sharma et al⁴¹ created a modified version of the Ishikawa diagnostic criteria for TKA in 1995 that does not consider a patient's age. Interestingly, patients having an age less than 40 was part of the obligatory criteria for the original Ishikawa diagnostic criteria, but the modified version not only does not have any obligatory criteria (only major and minor criteria) but also removes age as one of the diagnostic criteria for TKA. Instead, the presence of 1) 2 major criteria, 2) 1 major and 2 minor criteria, or 3) 4 minor criteria in a patient suggests a high probability that the patient suffers from TKA. The components of modified Ishikawa diagnostic criteria are:

Three Major Criteria

• 1. Left mid subclavian artery lesion
• 2. Right mid subclavian artery lesion
• 3. Characteristic signs and symptoms of at least 1month duration

Ten Minor Criteria

• 1. High ESR
• 2. Carotid artery tenderness
• 3. Hypertension
• 4. Aortic regurgitation or annuloaortic ectasia
• 5. Pulmonary artery lesion
• 6. Left mid common carotid lesion
• 7. Distal brachiocephalic trunk lesion
• 8. Descending thoracic aorta lesion
• 9. Abdominal aorta lesion
• 10. Coronary artery lesion

The modified Ishikawa diagnostic criteria for TKA has a sensitivity of 92.5% and a specificity of 95%, but there are certain vasculopathic risk factors in those under age 40 that may also serve as signs of TKA for clinicians, including³⁶:

• 1. Elevated acute phase reactants [eg, ESR or C = reactive protein (CRP)]
• 2. Carotidynia
• 3. Hypertension
• 4. >10 mm Hg difference in blood pressure between arms
• 5. Weak or absent peripheral pulses
• 6. Limb claudication
• 7. Arterial bruit
• 8. Angina

Diagnostic Procedures in TKA

Certain imaging modalities may be helpful in determining a diagnosis of TKA. Catheter and noncatheter angiography may be helpful in evaluating for luminal narrowing and arterial wall thickening.³⁶ However, in the early disease stages of TKA (ie, prestenotic), arterial wall thickening may be present without luminal narrowing.³⁶ This may be problematic in intra-arterial angiography, as it is confined to luminal viewing.³⁶

MRA and CTA are more advanced imaging modalities and allow for higher-quality and more extensive visualization. Gadolinium or iodine enhanced MRA and CTA can help visualize arterial wall thickening, edema, or enhancement in TKA, especially in the prestenotic phase.³⁶

A newer technique available is cardiovascular magnetic resonance (CMR); it is a single-technique imaging modality and allows for a versatile analysis of TKA. CMR may identify silent myocardial infarctions, atherosclerosis, and endothelial cell dysfunction in TKA patients.³⁶ The use of high-resolution color duplex ultrasound is possible in TKA but remains limited. Ultrasound may be used to help distinguish LVV from atherosclerosis and can help identify luminal narrowing or aneurysms.³³ Utilizing the same principles as in the diagnosis of GCA, ¹⁸F-FDG PET, and ¹⁸F-FDG PET/CT scans are increasingly popular in helping localize areas of vasculitis to diagnose TKA.^35,36

Ocular Imaging Techniques to Identify TKA

Certain imaging techniques may reveal ocular manifestations of TKA. In TKA-associated retinopathy with dilated retinal veins, fluorescein angiography can characterize ischemic or other abnormal features (eg, microaneurysms, arteriovenous shunts, retinal neovascularization, avascular areas).⁴² Thus, fluorescein angiography is considered the benchmark in evaluating for TKA- associated retinopathy.

Other ocular imaging techniques have been developed to complement fluorescein angiography. While macular manifestations of TKA-associated retinopathy are rare, OCTA may be able to discern macular ischemia (eg, enlargement of the foveal avascular zone) when other TKA-retinopathy changes are present.⁴³

In a case report, Tani et al demonstrated that Doppler Four- ier-domain OCT (DOCT) may show parabolic retinal blood velocity profiles (RBVP) during the systolic phase and abnormal RBVP during the diastolic phase in a patient with TKA with aortic regurgitation.⁴⁴ These ocular imaging techniques could be used by ophthalmologists as screening tools to identify patients that may have TKA and for whom it may be worthwhile to consider applying the modified Ishikawa diagnostic criteria.

TREATMENT

In general, GCA is predominantly treated medically, although there are certain cases in which surgery is necessary to repair occluded arteries affected by LVV (eg, subclavian, axillary, etc).⁴¹ In contrast, surgical treatment is often necessary in TKA. Surgical or endovascular revascularization of the heart may be necessary if medical therapy fails to sufficiently control LVV activity in TKA.³⁶

Similarities in Treatment Between GCA and TKA

GCA and TKA are systemic autoimmune disorders; thus, medical immunosuppressive treatment to control inflammation is generally required in both LVV disorders. Corticosteroids have remained as the mainstay pharmacotherapy for both GCA and TKA. Corticosteroid therapy has allowed for remission of TKA in up to 60% of patients. Moreover, corticosteroid therapy in GCA is typically successful in preventing further ischemic complication (eg, vision loss) and decreasing inflammation.^36,45

Unfortunately, long-term corticosteroid therapy has risks.⁴⁶ Multiple corticosteroid-sparing therapies have been developed in the treatment of both GCA and TKA. One potential treatment strategy is interleukin-6 (IL-6) blockade. IL-6 has been ascertained to be a prominent mediator of the systemic inflammatory response in both GCA and TKA.^47,48 Thus, IL-6 inhibitors (eg, tocilizumab, sarilumab, and satralizumab) and IL-6 receptor inhibitors (eg, siltuximab) are potential alternatives in the treatment of GCA and TKA. When used in combination with corticosteroids, IL-6 blockade allows for a shorter time span of corticosteroid use and reduced relapses; this helps decrease the possibility of corticosteroid-related side effects.^46,49,50 IL-6 blockade, however, lacks sufficient evidence to be an isolated treatment strategy in GCA and TKA; therefore, more research is necessary to ascertain the efficacy of IL-6 blockade.⁵¹

Another steroid-sparing option in LVV is mycophenolate mofetil (MMF). MMF is a purine synthesis inhibitor. Karabayaset al⁵² assessed the use of MMF for large-vessel GCA (LV- GCA).⁵² The study found that MMF in conjunction with corticosteroids was well tolerated and reduced the length of corticosteroid exposure. MMF has also been evaluated for treatment in TKA. Li et al⁵³ found that MMF may help decrease disease activity and lower corticosteroid dosage in TKA. Thus, MMF may offer promise as an immunosuppressive therapy, but more research and randomized control trials are necessary.

Differences in Treatment Between GCA and TKA

There are certain pharmacotherapies that have been shown to be more effective in TKA than in GCA. One specific therapy is tumor necrosis factor alpha (TNF-α) inhibitors (eg, infliximab, adalimumab) and TNF-α receptor inhibitors (eg, etanercept).^54,55 TNF-α is a proinflammatory cytokine that has been linked to the pathogenesis of GCA and TKA.^54,55 Comarmond et al⁵⁴ reported that anti-TNF-TNF-α therapy in cases of refractory TKA allowed for sustained complete remission in 37% of patients and partial remission in 53.5% of patients. However, 20% of patients experience side effects, and more research is necessary to evaluate the long-term efficacy and safety of anti-TNF-TNF-α therapy.⁵⁴ Unfortunately, the role of anti–TNF-TNF-α therapy is GCA has not been sufficiently explored.

Another pharmacotherapy that may be more effective in TKA than in GCA is Janus-kinase (JAK) inhibitors (eg, tofaci- tinib, ruxolitinib, baricitinib). The JAK/signal transducer and activator of transcription proteins (JAK/STAT) pathway has been linked to proinflammatory cascades in GCA and TKA.⁵⁵ JAK inhibitors may have some promise in the treatment of TKA.⁵⁵ However, more research is necessary to evaluate their efficacy and safety in both conditions.

Lastly, there are certain immunosuppressive therapies that seemingly lack randomized control trial studies. These include methotrexate, leflunomide, azathioprine, cyclophosphamide, rituximab, and ustekinumab (antibody targeting IL-12 and IL-23).⁵⁶ These treatments have been mainly offered as a second-line or combination therapy with corticosteroids, and offer some potential in refractory cases.⁵⁶

CONCLUSIONS

Although both GCA and TKA are LVV and share clinical and histological features, there is immunologic evidence that they are distinct pathologies. This correlates with the fact that both diseases manifest differently on ocular imaging. Additionally, GCA and TKA also differ in demographic and epidemiologic profile—GCA is more common in patients of Caucasian descent, while TKA is more common in patients of Asian descent. The TAB and temporal artery ultrasound are helpful in confirming the pathological diagnosis in GCA but the role of these procedures in TKA is unproven and remains ill-defined. Although age has been the predominant defining feature differentiating the LVV of TKA from GCA, there is increasing evidence for overlap in the demographics for these disorders. Although corticosteroids are the mainstay for therapy in both GCA and TKA, different immunotherapies based upon immunopathologic mechanisms in TKA and GCA may be necessary for these LVV. Surgical and endovascular therapy is more common in TKA than GCA. We compare and contrast both conditions in Table 1. Future research is necessary to further define the etiology, pathogenesis, and immunology of GCA and TKA.

Table 1 - Comparison of Symptoms, Ocular Features, and Initial Treatment of Takayasu Arteritis and Giant Cell Arteritis

	Takayasu Arteritis	Giant Cell Arteritis
Race (With Highest Risk)	Asian	Caucasian (Northern European)
Age At Onset	18–40	>50
Aortic Involvement	>90%	20–50%
Aortic Regurgitation	Frequent30–60%	Rare <10%
Vision Loss	Rare	2%
Ocular Complications	<10%	10–20%
Extravascular Manifestations	Fever of unknown origin, inflammatory bowel disease	Polymyalgia rheumatica, fever of unknown origin
Initial Management	Corticosteroids are mainstay	Corticosteroids are mainstay TNF-α inhibiting drugs and antibodies, and JAK inhibitors may be potential therapies

Adapted from Watanabe R, et al. Pathogenesis of giant cell arteritis and takayasu arteritis—similarities and Differences. Curr Rheumatol Rep. 2020;22.⁵⁷