FDG‐PET/CT of Giant Cell Arteritis with Normal Inflammatory Markers

Giant cell arteritis (GCA), the most common systemic vasculitis in the elderly, typically affects arteries arising from the aorta. While GCA rarely causes a stroke, its diagnosis is essential because patients with GCA and stroke have a high risk of mortality and require specific treatment. Here, we report a case of recurrent ischemic stroke due to intracranial GCA diagnosed using whole-body 18-fluoro-deoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) and vessel wall magnetic resonance imaging (VWMRI). A 79-year-old man with a history of hypertension, dyslipidemia, and past smoking presented to the hospital for dizziness and dysarthria following a 1-year history of mild shoulder pain and headache without associated visual acuity loss, field cuts, jaw claudication, or fever. Neurological examination showed dysarthria and ataxia of the right extremities. MRI revealed a cerebral infarction in the right cerebellar hemisphere and left medial pons due to right vertebral artery (VA) occlusion in the V4 segment. Considering the multiple conventional cardiovascular risk factors, a diagnosis of cerebral infarction secondary to atherosclerosis was made, prompting antithrombotic therapy. However, he gradually developed gait disturbances. MRI showed progression of the prior areas of infarction with a new infarct in the left middle cerebellar peduncle (Fig 1A). Laboratory tests revealed a normal C-reactive protein (CRP) level (0.44 mg/dL) and erythrocyte sedimentation rate (ESR; 16 mm/h). VWMRI demonstrated concentric arterial wall thickening with enhancement in both VAs (Fig 1B, white arrowheads). Computed tomography angiography (CTA) and cerebral angiography showed the pearl-and-string sign in bilateral VAs and occlusion in the right V4 segment (Fig 1G, white arrowheads). Whole-body FDG-PET/CT revealed increased glucose uptake in the shoulder and hip joints, bilateral VAs, and temporal arteries (white arrowheads in Fig 1C, D, and red arrowheads in Fig 1H). Subsequently, a 2-cm-long left temporal artery biopsy was performed. Hematoxylin and eosin-stained sections of the temporal artery (Fig 1E) revealed lymphocytic infiltration from the adventitia to media and intimal hyperplasia with luminal narrowing. Elastica van Gieson-stained sections (Fig 1F, black arrow and arrowhead, respectively) demonstrated multinucleated giant cells involving fragments of the internal elastic lamina. These findings were suggestive of GCA, prompting administration of methylprednisolone (500 mg) for 3 days followed by oral prednisolone (1 mg/kg). However, the posterior circulation infarcts gradually increased. He later received weekly tocilizumab, but the cerebral infarcts progressed. Additional treatment with 6 cycles of cyclophosphamide (500 mg/m2) every 3 weeks and oral azathioprine halted the recurrence of stroke. FDG-PET/CT revealed significant reductions in FDG accumulation in bilateral VAs (Fig 1I). To the best of our knowledge, GCA rarely causes ischemic stroke. However, it is important to consider GCA and atherosclerosis as differential diagnoses, especially in the elderly, due to their poor prognosis and high risk for mortality.1 Although there are no specific laboratory markers for GCA, elevated inflammatory markers, such as CRP and ESR, may help clinicians suspect GCA. Contrastingly, the prevalence of biopsy-proven GCA with normal CRP and ESR is rare and reported as 0.8–4%.2, 3 This atypical finding might delay the diagnosis of GCA.2 In our case, GCA was not suspected initially due to the lack of inflammation. However, the presence of the pearl-and-string sign on CTA and angiogram increased the suspicion for vasculitis. Thus, our case illustrates that GCA should be considered as a differential diagnosis even in case of normal inflammatory markers. In patients with GCA, FDG-PET/CT is a useful modality for identifying large vessel inflammation.1 In a meta-analysis of four pooled studies, FDG-PET/CT showed a high sensitivity (90%) and specificity (98%) for the diagnosis of GCA.4 In our patient, FDG-PET/CT revealed vascular mural inflammation, prompting early diagnosis with biopsy and treatment with immunosuppressive agents. This report highlights the importance of performing vascular imaging and FDG-PET/CT for early diagnosis and treatment of GCA in elderly patients with recurrent posterior circulation ischemic stroke, even if their inflammatory markers are normal. No funding or sponsorship was received in connection with this manuscript. J.T., N.O., and M.K. contributed to the conception and design of the study. N.K. and J.T. contributed to data acquisition and analysis. N.K. and J.T. contributed to drafting the manuscript and preparing the figures. Nothing to report.