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Objective: Somatic variants in UBA1 cause VEXAS, a recently described, systemic autoinflammatory disease. Research on VEXAS has largely focused on highly symptomatic patients. We sought to determine the prevalence of canonical, VEXAS‐associated somatic variants and their disease penetrance in a diverse, unselected population. Methods: We analyzed clinical‐grade whole genome sequencing data from 245,368 participants in the All of Us Research Program. We compared persons carrying a canonical VEXAS‐associated somatic variant to age, sex, and ancestry matched controls across the domains of diagnoses, medications, and laboratory values. Results: 74 participants were identified who carry one VEXAS‐defining somatic variant, UBA1 c.121A>C, p.Met41Leu. The variant allele fraction ranged from 4.5% to 33%. No other canonical VEXAS‐associated variants were identified. Of the 74 carriers, 62 (84%) were women, 20 (27%) were African American, and 14 (19%) were American Admixed/Latino. There was no statistically significant association between case/control status and any VEXAS‐associated diagnosis code, medication prescription, or laboratory value. Conclusion: We report the largest cohort to date of persons with the VEXAS‐associated p.Met41Leu somatic variant. This cohort differed substantially from reported cohorts of patients with clinical VEXAS, having a higher proportion of persons who were young, female, and of diverse ancestry. Variant allele fractions were lower than reported in clinical VEXAS cohorts, and bioinformatic analysis detected no clinical manifestations of VEXAS. Thus, the UBA1 p.Met41Leu somatic variant displayed incomplete penetrance for VEXAS. Further study is needed to determine the natural history of VEXAS‐associated somatic variants in the predisease phase. [ABSTRACT FROM AUTHOR]

Objective: To develop and validate classification criteria for microscopic polyangiitis (MPA).Methods: Patients with vasculitis or comparator diseases were recruited into an international cohort. The study proceeded in five phases: (1) identification of candidate items using consensus methodology, (2) prospective collection of candidate items present at the time of diagnosis, (3) data-driven reduction of the number of candidate items, (4) expert panel review of cases to define the reference diagnosis and (5) derivation of a points-based risk score for disease classification in a development set using least absolute shrinkage and selection operator logistic regression, with subsequent validation of performance characteristics in an independent set of cases and comparators.Results: The development set for MPA consisted of 149 cases of MPA and 408 comparators. The validation set consisted of an additional 142 cases of MPA and 414 comparators. From 91 candidate items, regression analysis identified 10 items for MPA, 6 of which were retained. The final criteria and their weights were as follows: perinuclear antineutrophil cytoplasmic antibody (ANCA) or anti-myeloperoxidase-ANCA positivity (+6), pauci-immune glomerulonephritis (+3), lung fibrosis or interstitial lung disease (+3), sino-nasal symptoms or signs (-3), cytoplasmic ANCA or anti-proteinase 3 ANCA positivity (-1) and eosinophil count ≥1×109/L (-4). After excluding mimics of vasculitis, a patient with a diagnosis of small- or medium-vessel vasculitis could be classified as having MPA with a cumulative score of ≥5 points. When these criteria were tested in the validation data set, the sensitivity was 91% (95% CI 85% to 95%) and the specificity was 94% (95% CI 92% to 96%).Conclusion: The 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for MPA are now validated for use in clinical research. [ABSTRACT FROM AUTHOR]

Objective: To provide evidence‐based recommendations and expert guidance for the management of antineutrophil cytoplasmic antibody–associated vasculitis (AAV), including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Methods: Clinical questions regarding the treatment and management of AAV were developed in the population, intervention, comparator, and outcome (PICO) format (47 for GPA/MPA, 34 for EGPA). Systematic literature reviews were conducted for each PICO question. The Grading of Recommendations Assessment, Development and Evaluation methodology was used to assess the quality of evidence and formulate recommendations. Each recommendation required ≥70% consensus among the Voting Panel. Results: We present 26 recommendations and 5 ungraded position statements for GPA/MPA, and 15 recommendations and 5 ungraded position statements for EGPA. This guideline provides recommendations for remission induction and maintenance therapy as well as adjunctive treatment strategies in GPA, MPA, and EGPA. These recommendations include the use of rituximab for remission induction and maintenance in severe GPA and MPA and the use of mepolizumab in nonsevere EGPA. All recommendations are conditional due in part to the lack of multiple randomized controlled trials and/or low‐quality evidence supporting the recommendations. Conclusion: This guideline presents the first recommendations endorsed by the American College of Rheumatology and the Vasculitis Foundation for the management of AAV and provides guidance to health care professionals on how to treat these diseases. [ABSTRACT FROM AUTHOR]

Objective: To provide evidence‐based recommendations and expert guidance for the management of giant cell arteritis (GCA) and Takayasu arteritis (TAK) as exemplars of large vessel vasculitis. Methods: Clinical questions regarding diagnostic testing, treatment, and management were developed in the population, intervention, comparator, and outcome (PICO) format for GCA and TAK (27 for GCA, 27 for TAK). Systematic literature reviews were conducted for each PICO question. The Grading of Recommendations Assessment, Development and Evaluation methodology was used to rate the quality of the evidence. Recommendations were developed by the Voting Panel, comprising adult and pediatric rheumatologists and patients. Each recommendation required ≥70% consensus among the Voting Panel. Results: We present 22 recommendations and 2 ungraded position statements for GCA, and 20 recommendations and 1 ungraded position statement for TAK. These recommendations and statements address clinical questions relating to the use of diagnostic testing, including imaging, treatments, and surgical interventions in GCA and TAK. Recommendations for GCA include support for the use of glucocorticoid‐sparing immunosuppressive agents and the use of imaging to identify large vessel involvement. Recommendations for TAK include the use of nonglucocorticoid immunosuppressive agents with glucocorticoids as initial therapy. There were only 2 strong recommendations; the remaining recommendations were conditional due to the low quality of evidence available for most PICO questions. Conclusion: These recommendations provide guidance regarding the evaluation and management of patients with GCA and TAK, including diagnostic strategies, use of pharmacologic agents, and surgical interventions. [ABSTRACT FROM AUTHOR]

Objectives. Advances in diagnostic techniques have led to better distinction between types of vasculitis, potentially affecting the utility of the 1990 ACR classification criteria for vasculitis. This study tested the performance of these criteria in a contemporary vasculitis cohort. Methods. The Diagnosis and Classification in Vasculitis Study provided detailed clinical, serological, pathological and radiological data from patients with primary systemic vasculitis and clinical context- specific comparator conditions. Fulfilment of six ACR criteria sets and their diagnostic performance was evaluated in patients with a given type of vasculitis and its comparator conditions. Results. Data from 1095 patients with primary systemic vasculitis and 415 with comparator conditions were available. For classification, sensitivities and specificities for ACR classification criteria were, respectively, 81.1% and 94.9% for GCA; 73.6% and 98.3% for Takayasu's arteritis; 65.6% and 88.7% for granulomatosis with polyangiitis; 57.0% and 99.8% for eosinophilic granulomatosis with polyangiitis; 40.6% and 87.8% for polyarteritis nodosa; 28.9% and 88.5% for microscopic polyangiitis; and 72.7% and 96.3% for IgA-vasculitis. Overall sensitivity was 67.1%. Of cases identified by their respective criteria, 16.9% also met criteria for other vasculitides. Diagnostic specificity ranged from 64.2 to 98.9%; overall, 113/415 comparators (27.2%) fulfilled at least one of the ACR classification criteria sets. Conclusion. Since publication of the ACR criteria for vasculitis, the sensitivity for each type of vasculitis, except GCA, has diminished, although the specificities have remained high, highlighting the need for updated classification criteria. [ABSTRACT FROM AUTHOR]

Importance: VEXAS (vacuoles, E1-ubiquitin-activating enzyme, X-linked, autoinflammatory, somatic) syndrome is a disease with rheumatologic and hematologic features caused by somatic variants in UBA1. Pathogenic variants are associated with a broad spectrum of clinical manifestations. Knowledge of prevalence, penetrance, and clinical characteristics of this disease have been limited by ascertainment biases based on known phenotypes., Objective: To determine the prevalence of pathogenic variants in UBA1 and associated clinical manifestations in an unselected population using a genomic ascertainment approach., Design, Setting, and Participants: This retrospective observational study evaluated UBA1 variants in exome data from 163 096 participants within the Geisinger MyCode Community Health Initiative. Clinical phenotypes were determined from Geisinger electronic health record data from January 1, 1996, to January 1, 2022., Exposures: Exome sequencing was performed., Main Outcomes and Measures: Outcome measures included prevalence of somatic UBA1 variation; presence of rheumatologic, hematologic, pulmonary, dermatologic, and other findings in individuals with somatic UBA1 variation on review of the electronic health record; review of laboratory data; bone marrow biopsy pathology analysis; and in vitro enzymatic assays., Results: In 163 096 participants (mean age, 52.8 years; 94% White; 61% women), 11 individuals harbored likely somatic variants at known pathogenic UBA1 positions, with 11 of 11 (100%) having clinical manifestations consistent with VEXAS syndrome (9 male, 2 female). A total of 5 of 11 individuals (45%) did not meet criteria for rheumatologic and/or hematologic diagnoses previously associated with VEXAS syndrome; however, all individuals had anemia (hemoglobin: mean, 7.8 g/dL; median, 7.5 g/dL), which was mostly macrocytic (10/11 [91%]) with concomitant thrombocytopenia (10/11 [91%]). Among the 11 patients identified, there was a pathogenic variant in 1 male participant prior to onset of VEXAS-related signs or symptoms and 2 female participants had disease with heterozygous variants. A previously unreported UBA1 variant (c.1861A>T; p.Ser621Cys) was found in a symptomatic patient, with in vitro data supporting a catalytic defect and pathogenicity. Together, disease-causing UBA1 variants were found in 1 in 13 591 unrelated individuals (95% CI, 1:7775-1:23 758), 1 in 4269 men older than 50 years (95% CI, 1:2319-1:7859), and 1 in 26 238 women older than 50 years (95% CI, 1:7196-1:147 669)., Conclusions and Relevance: This study provides an estimate of the prevalence and a description of the clinical manifestations of UBA1 variants associated with VEXAS syndrome within a single regional health system in the US. Additional studies are needed in unselected and genetically diverse populations to better define general population prevalence and phenotypic spectrum.

Objective: To develop and validate new classification criteria for Takayasu arteritis (TAK)., Methods: Patients with vasculitis or comparator diseases were recruited into an international cohort. The study proceeded in 6 phases: 1) identification of candidate criteria items, 2) collection of candidate items present at diagnosis, 3) expert panel review of cases, 4) data-driven reduction of candidate items, 5) derivation of a points-based classification score in a development data set, and 6) validation in an independent data set., Results: The development data set consisted of 316 cases of TAK and 323 comparators. The validation data set consisted of an additional 146 cases of TAK and 127 comparators. Age ≤60 years at diagnosis and imaging evidence of large-vessel vasculitis were absolute requirements to classify a patient as having TAK. The final criteria items and weights were as follows: female sex (+1), angina (+2), limb claudication (+2), arterial bruit (+2), reduced upper extremity pulse (+2), reduced pulse or tenderness of a carotid artery (+2), blood pressure difference between arms of ≥20 mm Hg (+1), number of affected arterial territories (+1 to +3), paired artery involvement (+1), and abdominal aorta plus renal or mesenteric involvement (+3). A patient could be classified as having TAK with a cumulative score of ≥5 points. When these criteria were tested in the validation data set, the model area under the curve was 0.97 (95% confidence interval [95% CI] 0.94-0.99) with a sensitivity of 93.8% (95% CI 88.6-97.1%) and specificity of 99.2% (95% CI 96.7-100.0%)., Conclusion: The 2022 American College of Rheumatology/EULAR classification criteria for TAK are now validated for use in research., (© 2022 American College of Rheumatology.)

Objective: To provide evidence-based recommendations and expert guidance for the management of Kawasaki disease (KD), focusing on clinical scenarios more commonly addressed by rheumatologists., Methods: Sixteen clinical questions regarding diagnostic testing, treatment, and management of KD were developed in the Patient/Population, Intervention, Comparison, and Outcomes (PICO) question format. Systematic literature reviews were conducted for each PICO question. We used the Grading of Recommendations, Assessment, Development and Evaluation method to assess the quality of evidence and formulate recommendations. Each recommendation required consensus from at least 70% of the Voting Panel., Results: We present 1 good practice statement, 11 recommendations, and 1 ungraded position statement to guide the management of KD and clinical scenarios of suspected KD. These recommendations for KD are focused on situations in which input from rheumatologists may be requested by other managing specialists, such as in cases of treatment-refractory, severe, or complicated KD. The good practice statement affirms that all patients with KD should receive initial treatment with intravenous immunoglobulin (IVIG). In addition, we developed 7 strong and 4 conditional recommendations for the management of KD or suspected KD. Strong recommendations include prompt treatment of incomplete KD, treatment with aspirin, and obtaining an echocardiogram in the setting of unexplained macrophage activation syndrome or shock. Conditional recommendations include use of IVIG with other adjuvant agents for patients with KD and high-risk features of IVIG resistance and/or coronary artery aneurysms. These recommendations endorse minimizing risk to the patient by using established therapy promptly at disease onset and identifying situations in which adjunctive therapy may be warranted., Conclusion: These recommendations provide guidance regarding diagnostic strategies, use of pharmacologic agents, and use of echocardiography in patients with suspected or confirmed KD., (© 2022 American College of Rheumatology. This article has been contributed to by US Government employees and their work is in the public domain in the USA.)

Objective: To develop and validate revised classification criteria for eosinophilic granulomatosis with polyangiitis (EGPA)., Methods: Patients with vasculitis or comparator diseases were recruited into an international cohort. The study proceeded in five phases: (1) identification of candidate criteria items using consensus methodology, (2) prospective collection of candidate items present at the time of diagnosis, (3) data-driven reduction of the number of candidate items, (4) expert panel review of cases to define the reference diagnosis and (5) derivation of a points-based risk score for disease classification in a development set using least absolute shrinkage and selection operator logistic regression, with subsequent validation of performance characteristics in an independent set of cases and comparators., Results: The development set for EGPA consisted of 107 cases of EGPA and 450 comparators. The validation set consisted of an additional 119 cases of EGPA and 437 comparators. From 91 candidate items, regression analysis identified 11 items for EPGA, 7 of which were retained. The final criteria and their weights were as follows: maximum eosinophil count ≥1×10 9 /L (+5), obstructive airway disease (+3), nasal polyps (+3), cytoplasmic antineutrophil cytoplasmic antibody (ANCA) or anti-proteinase 3-ANCA positivity (-3), extravascular eosinophilic predominant inflammation (+2), mononeuritis multiplex/motor neuropathy not due to radiculopathy (+1) and haematuria (-1). After excluding mimics of vasculitis, a patient with a diagnosis of small- or medium-vessel vasculitis could be classified as having EGPA if the cumulative score was ≥6 points. When these criteria were tested in the validation data set, the sensitivity was 85% (95% CI 77% to 91%) and the specificity was 99% (95% CI 98% to 100%)., Conclusion: The 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology Classification Criteria for Eosinophilic Granulomatosis with Polyangiitis demonstrate strong performance characteristics and are validated for use in research., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To develop and validate revised classification criteria for granulomatosis with polyangiitis (GPA)., Methods: Patients with vasculitis or comparator diseases were recruited into an international cohort. The study proceeded in five phases: (1) identification of candidate criteria items using consensus methodology, (2) prospective collection of candidate items present at the time of diagnosis, (3) data-driven reduction of the number of candidate items, (4) expert panel review of cases to define the reference diagnosis and (5) derivation of a points-based risk score for disease classification in a development set using least absolute shrinkage and selection operator logistic regression, with subsequent validation of performance characteristics in an independent set of cases and comparators., Results: The development set for GPA consisted of 578 cases of GPA and 652 comparators. The validation set consisted of an additional 146 cases of GPA and 161 comparators. From 91 candidate items, regression analysis identified 26 items for GPA, 10 of which were retained. The final criteria and their weights were as follows: bloody nasal discharge, nasal crusting or sino-nasal congestion (+3); cartilaginous involvement (+2); conductive or sensorineural hearing loss (+1); cytoplasmic antineutrophil cytoplasmic antibody (ANCA) or anti-proteinase 3 ANCA positivity (+5); pulmonary nodules, mass or cavitation on chest imaging (+2); granuloma or giant cells on biopsy (+2); inflammation or consolidation of the nasal/paranasal sinuses on imaging (+1); pauci-immune glomerulonephritis (+1); perinuclear ANCA or antimyeloperoxidase ANCA positivity (-1); and eosinophil count ≥1×10 9  /L (-4). After excluding mimics of vasculitis, a patient with a diagnosis of small- or medium-vessel vasculitis could be classified as having GPA if the cumulative score was ≥5 points. When these criteria were tested in the validation data set, the sensitivity was 93% (95% CI 87% to 96%) and the specificity was 94% (95% CI 89% to 97%)., Conclusion: The 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for GPA demonstrate strong performance characteristics and are validated for use in research., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: Mouth and genital ulcers with inflamed cartilage (MAGIC) syndrome is characterized by overlapping features of relapsing polychondritis (RP) and Behcet's disease (BD). To date, no studies have defined the clinical spectrum of disease in a cohort of patients with MAGIC syndrome., Methods: Adult patients within an ongoing prospective, observational cohort study in RP were clinically assessed for MAGIC syndrome. A systematic review was conducted to identify additional cases of MAGIC syndrome by searching four databases: PubMed (US National Library of Medicine), Embase (Elsevier), Scopus (Elsevier) and Web of Science: Core Collection (Clarivate Analytics). The inclusion criteria used were: [1] patients of any age or gender who were diagnosed with MAGIC syndrome, or both RP and BD; [2] case report or case series study; [3] published from 1985 - July 2020; and [4] in English language. Risk of bias was assessed using a checklist developed by the authors and based on the Consensus-based Clinical Case Reporting (CARE) Guidelines. Search results screening, article inclusion, data extraction and risk of bais assessment was performed independently by two investigators. Clinical characteristics, particularly BD-related features, were compared between patients with MAGIC syndrome and cases of non-MAGIC RP. The performance characteristics of different criteria to classify MAGIC syndrome were also evaluated., Results: Out of 96 patients with RP, 13 (14%) patients were diagnosed with MAGIC syndrome. For the systematic review, 380 articles were retrieved of which 90 were screened at title and abstract levels. Of these screened, 60 were excluded and 30 proceeded to full text review where an additional 8 were excluded. Twenty-two articles were included in our review and from which 27 additional cases of MAGIC syndrome were identified. Pooling all 40 cases together and comparing them with non-MAGIC RP, there was a significantly higher prevalence of ocular involvement (28% vs 4%, p<0.01), cutaneous involvement (35% vs 1%, p<0.01), GI involvement (23% vs 4%, p<0.01), and CNS involvement (8% vs 0, p = 0.04) in MAGIC syndrome. A higher prevalence of aortitis (23% vs 1%, p<0.01), Raynaud's phenomenon (54% vs 11%, p<0.01), and elevated anti-collagen II antibodies (50% vs 9%, p = 0.04) were observed in MAGIC syndrome. Fulfillment of either McAdam's or Damiani's Criteria for RP plus the International Criteria for Behçet's Disease had excellent sensitivity (98%) to classify cases of MAGIC syndrome., Conclusion: A substantial proportion of patients with RP can be clinically diagnosed with MAGIC syndrome. These patients have features of RP, BD, and other unique features including aortitis, Raynaud's phenomenon and elevated anti-collagen II antibodies., Competing Interests: Declaration of Competing Interest None., (Copyright © 2021. Published by Elsevier Inc.)

Noncerebral vasculitis is a wide-range noninfectious inflammatory disorder affecting the vessels. Vasculitides have been categorized based on the vessel size, such as large-vessel vasculitis, medium-vessel vasculitis, and small-vessel vasculitis. In this document, we cover large-vessel vasculitis and medium-vessel vasculitis. Due to the challenges of vessel biopsy, imaging plays a crucial role in diagnosing this entity. While CTA and MRA can both provide anatomical details of the vessel wall, including wall thickness and enhancement in large-vessel vasculitis, FDG-PET/CT can show functional assessment based on the glycolytic activity of inflammatory cells in the inflamed vessels. Given the size of the vessel in medium-vessel vasculitis, invasive arteriography is still a choice for imaging. However, high-resolution CTA images can depict small-caliber aneurysms, and thus can be utilized in the diagnosis of medium-vessel vasculitis. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment., (Copyright © 2021 American College of Radiology. Published by Elsevier Inc. All rights reserved.)

Objective: To provide evidence-based recommendations and expert guidance for the management of systemic polyarteritis nodosa (PAN)., Methods: Twenty-one clinical questions regarding diagnostic testing, treatment, and management were developed in the population, intervention, comparator, and outcome (PICO) format for systemic, non-hepatitis B-related PAN. Systematic literature reviews were conducted for each PICO question. The Grading of Recommendations Assessment, Development and Evaluation methodology was used to assess the quality of evidence and formulate recommendations. Each recommendation required ≥70% consensus among the Voting Panel., Results: We present 16 recommendations and 1 ungraded position statement for PAN. Most recommendations were graded as conditional due to the paucity of evidence. These recommendations support early treatment of severe PAN with cyclophosphamide and glucocorticoids, limiting toxicity through minimizing long-term exposure to both treatments, and the use of imaging and tissue biopsy for disease diagnosis. These recommendations endorse minimizing risk to the patient by using established therapy at disease onset and identify new areas where adjunctive therapy may be warranted., Conclusion: These recommendations provide guidance regarding diagnostic strategies, use of pharmacologic agents, and imaging for patients with PAN., (© 2021 American College of Rheumatology. This article has been contributed to by US Government employees and their work is in the public domain in the USA.)

Objective: To assess patient-reported symptoms and burden of disease in relapsing polychondritis (RP)., Methods: Patients with RP completed a disease-specific online survey to identify symptoms attributed to illness. Patients were divided into subgroups based upon presence or absence of ear/nose, airway, or joint involvement. Pathway to diagnosis, treatment, and disease-related complications were assessed within each subgroup., Results: Data from 304 respondents were included in this analysis. Prior to diagnosis, most patients with RP went to the emergency room (54%), saw > 3 physicians (54%), and had symptoms for >5 years (64%). A concomitant diagnosis of fibromyalgia and absence of ear/nose or joint involvement was associated with diagnostic delay >1 year. Common diagnoses prior to RP diagnosis included asthma in patients with airway involvement (35% versus 22%; P = 0.03) and ear infection in patients with ear/nose involvement (51% versus 6%; P < 0.01). Patients with joint involvement were more likely to receive a glucocorticoid-sparing agent (85% versus 13%; P < 0.01). Most patients reported a major complication, including disability (25%), tracheomalacia (16%), or hearing loss (34%). Patients with airway involvement reported more tracheomalacia (20% versus 4%; P < 0.01). Disability (24% versus 7%; P < 0.01) and hearing loss (39% versus 11%; P < 0.01) were prevalent in the joint involvement subgroup., Conclusion: Patient-reported data in RP highlight a significant burden of disease. Patterns of organ involvement may lead to diagnostic delay and influence treatment decisions, ultimately impacting the development of disease-related complications. Timely diagnosis, standardization of treatment approaches, and prevention of disease-related complications are major unmet needs in RP., (Published 2017. This article is a U.S. Government work and is in the public domain in the USA.)

Objectives: To compare patterns of arteriographic lesions of the aorta and primary branches in patients with Takayasu's arteritis (TAK) and giant cell arteritis (GCA)., Methods: Patients were selected from two North American cohorts of TAK and GCA. The frequency of arteriographic lesions was calculated for 15 large arteries. Cluster analysis was used to derive patterns of arterial disease in TAK versus GCA and in patients categorised by age at disease onset. Using latent class analysis, computer derived classification models based upon patterns of arterial disease were compared with traditional classification., Results: Arteriographic lesions were identified in 145 patients with TAK and 62 patients with GCA. Cluster analysis demonstrated that arterial involvement was contiguous in the aorta and usually symmetric in paired branch vessels for TAK and GCA. There was significantly more left carotid (p=0.03) and mesenteric (p=0.02) artery disease in TAK and more left and right axillary (p<0.01) artery disease in GCA. Subclavian disease clustered asymmetrically in TAK and in patients ≤55 years at disease onset and clustered symmetrically in GCA and patients >55 years at disease onset. Computer derived classification models distinguished TAK from GCA in two subgroups, defining 26% and 18% of the study sample; however, 56% of patients were classified into a subgroup that did not strongly differentiate between TAK and GCA., Conclusions: Strong similarities and subtle differences in the distribution of arterial disease were observed between TAK and GCA. These findings suggest that TAK and GCA may exist on a spectrum within the same disease.