Department of Otorhinolaryngology, St. Peter's Hospital, Brussels, Belgium.
Department of Otorhinolaryngology, St. Peter's Hospital, Brussels, Belgium.
Med Hypotheses. 2020 Oct;143:109881. doi: 10.1016/j.mehy.2020.109881. Epub 2020 May 26.
Since the outbreak of Coronavirus Disease 2019 (COVID-19), loss of smell has increasingly been reported as a frequent clinical sign. Understanding the underlying mechanism and the prognostic value of this symptom will help better manage patients. SARS-CoV-2, as SARS-CoV-1, may likely spread to the central nervous system (CNS) via the olfactory nerve, a known gateway for respiratory neurotropic viruses. We hypothesise that sudden loss of smell due to COVID-19 is the consequence of a protective host defence mechanism involving apoptosis of olfactory receptor neurons. Sacrificing smelling over neuroprotection is a logical strategy, even more so as olfaction is the only sense with the ability to regenerate in adults. Induced apoptosis of olfactory neurons has been shown in mice, successfully preventing neuroinvasion. On the other hand, adult olfactory neurogenesis has been shown to be regulated in part by the immune system, allowing to restore olfactory function. Understanding anosmia as part of a defence mechanism would support the concept of sudden anosmia as being a positive prognostic factor in the short term. Also, it may orient research to investigate the risk of future neurodegenerative disease linked to persisting coronavirus in neurons.
自 2019 年冠状病毒病（COVID-19）爆发以来，嗅觉丧失越来越多地被报道为一种常见的临床症状。了解这种症状的潜在机制和预后价值将有助于更好地管理患者。与 SARS-CoV-1 一样，SARS-CoV-2 可能通过嗅神经传播到中枢神经系统（CNS），嗅神经是呼吸道神经嗜性病毒的已知门户。我们假设，COVID-19 导致的突然嗅觉丧失是涉及嗅觉受体神经元凋亡的保护性宿主防御机制的结果。为了神经保护而牺牲嗅觉是一种合理的策略，尤其是因为嗅觉是唯一具有在成人中再生能力的感觉。在小鼠中已经证明了嗅觉神经元的诱导性凋亡可以成功地阻止神经入侵。另一方面，成年嗅觉神经发生部分受免疫系统调控，从而可以恢复嗅觉功能。将嗅觉丧失理解为防御机制的一部分，可以支持突然嗅觉丧失作为短期预后良好的因素的概念。此外，这可能会促使研究调查与神经元中持续存在的冠状病毒相关的未来神经退行性疾病的风险。
