Objectives: Sudden loss of smell is a very common symptom of coronavirus disease 19 (COVID-19). This study characterizes the structural and metabolic cerebral correlates of dysosmia in patients with COVID-19. Methods: Structural brain magnetic resonance imaging (MRI) and positron emission tomography with [18F]-fluorodeoxyglucose (FDG-PET) were prospectively acquired simultaneously on a hybrid PET-MR in twelve patients (2 males, 10 females, mean age: 42.6 years, age range: 23-60 years) with sudden dysosmia and positive detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on nasopharyngeal swab specimens. FDG-PET data were analysed using a voxel-based approach and compared with that of a group of healthy subjects. Results: Bilateral blocking of the olfactory cleft was observed in six patients, while subtle olfactory bulb asymmetry was found in three patients. No MRI signal abnormality downstream of the olfactory tract was observed. Heterogeneous (decrease or increase) glucose metabolism abnormalities were observed in core olfactory and high-order neocortical areas. A modulation of regional cerebral glucose metabolism by the severity and the duration of COVID-19-related dysosmia was disclosed using correlation analyses. Conclusions: This PET-MR study shows that sudden loss of smell in COVID-19 is not related to central involvement due to SARS-CoV-2 neuroinvasiveness. Loss of smell is associated with heterogeneous cerebral metabolic changes in core olfactory and high-order cortical areas likely related to combined processes of deafferentation and active functional reorganisation secondary to the lack of olfactory stimulation.

中文翻译：

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突然失去嗅觉的COVID-19患者的结构和代谢性脑异常

目的：突然的气味消失是冠状病毒病19（COVID-19）的一种非常常见的症​​状。这项研究的特点是结构障碍和代谢性脑瘫患者COVID-19的大脑。方法：前瞻性地在混合PET-MR上同时获得了12例患者（2例男性，10例女性，平均年龄：42.6岁）的结构性脑磁共振成像（MRI）和[18F]-氟脱氧葡萄糖（FDG-PET）的正电子发射断层扫描，年龄范围：23至60岁），伴有突然的呼吸困难，并在鼻咽拭子标本上发现了严重的急性呼吸综合征冠状病毒2（SARS-CoV-2）。使用基于体素的方法分析FDG-PET数据，并将其与一组健康受试者的数据进行比较。结果：6例患者观察到双侧嗅裂阻塞，而三名患者发现了轻微的嗅球不对称。嗅觉下游未见MRI信号异常。在核心嗅觉区和高级皮质区观察到异质（减少或增加）葡萄糖代谢异常。使用相关性分析揭示了COVID-19相关性睡眠障碍的严重程度和持续时间对局部脑葡萄糖代谢的调节。结论：这项PET-MR研究表明，由于SARS-CoV-2神经侵袭，COVID-19中的突然气味散发与中枢受累无关。气味的丧失与核心嗅觉和高级皮质区域的异质性脑代谢变化有关，这可能与由于缺乏嗅觉刺激而引起的脱除咖啡因和主动功能重组的综合过程有关。