Khoury Julie A, Hoxworth Joseph M, Mazlumzadeh Mehrdad, Wellik Kay E, Wingerchuk Dean M, Demaerschalk Bart M
Department of Neurology, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA.
Neurologist. 2008 Sep;14(5):330-5. doi: 10.1097/NRL.0b013e3181836add.
Giant cell arteritis (GCA) is a relatively common form of systemic vasculitis, known for its predisposition to affect extracranial branches of the carotid artery and associated potential for causing visual loss and stroke. Neurologists need to be vigilant for this disorder, diagnose it early, and institute effective corticosteroid therapy. The differential diagnosis can be broad. Unfortunately, all clinical and laboratory features of GCA are limited by either low sensitivity or low specificity. Temporal artery biopsy remains the gold standard, but it has its own limitations. Noninvasive imaging techniques, like magnetic resonance imaging (MRI), may be capable of detecting the occurrence of GCA.
How useful is high resolution MRI as a diagnostic test in establishing the diagnosis of GCA?
We addressed the question through development of a structured critically appraised topic. Participants included consultant and resident neurologists, clinical epidemiologists, medical librarian, and clinical content experts in the field of neuroradiology, rheumatology, and vascular neurology. Participants started with a clinical scenario and a structured question, devised search strategies, located and compiled the best evidence, performed critical appraisals, synthesized the results, summarized the evidence, provided commentary, and declared bottom-line conclusions.
A single study which assessed the diagnostic value of MRI against a reference standard in GCA was appraised. For the MRI, the estimated sensitivity was 81% (95% CI 67-95), specificity was 97% (91-100), positive likelihood ratio (LR) was 26.6 (95% CI 3.8-184.8), negative LR was 0.20 (95% CI 0.10-0.41). The study exhibited several methodological weaknesses which interfered with its validity.
The specificity and positive LR of high resolution MRI are sufficiently high that a positive MRI combined with other clinical and laboratory data consistent with GCA may be useful in diagnosing GCA. Given the relatively low sensitivity of the test, a negative MRI would not be sufficient to rule out the diagnosis of GCA.
巨细胞动脉炎（GCA）是一种相对常见的系统性血管炎，其特点是易累及颈动脉的颅外分支，并具有导致视力丧失和中风的潜在风险。神经科医生需要对这种疾病保持警惕，早期诊断并开展有效的皮质类固醇治疗。其鉴别诊断范围可能很广。不幸的是，GCA的所有临床和实验室特征都存在敏感性低或特异性低的问题。颞动脉活检仍是金标准，但也有其自身局限性。像磁共振成像（MRI）这样的非侵入性成像技术可能能够检测到GCA的发生。
高分辨率MRI作为诊断GCA的诊断试验有多大用处？
我们通过制定一个结构化的严格评价主题来解决这个问题。参与者包括顾问和住院神经科医生、临床流行病学家、医学图书馆员以及神经放射学、风湿病学和血管神经病学领域的临床内容专家。参与者从一个临床病例和一个结构化问题开始，设计搜索策略，查找并汇编最佳证据，进行严格评价，综合结果，总结证据，提供评论，并得出最终结论。
评估了一项针对GCA中MRI相对于参考标准的诊断价值的单一研究。对于MRI，估计敏感性为81%（95%CI 67-95），特异性为97%（91-100），阳性似然比（LR）为26.6（95%CI 3.8-184.8），阴性LR为0.20（95%CI 0.10-0.41）。该研究存在几个方法学上的弱点，影响了其有效性。
高分辨率MRI的特异性和阳性LR足够高，以至于阳性MRI结合其他与GCA一致的临床和实验室数据可能有助于诊断GCA。鉴于该检查的敏感性相对较低，阴性MRI不足以排除GCA的诊断。
