Olfactory nerve: from ugly duckling to swan

ABSTRACT Background: The olfactory nerve has never been the shining star of neurological examination. Quite the contrary, examining the first cranial nerve is often an overlooked step. As cases of anosmia secondary to COVID-19 infection continue to rise, the 2020 pandemic has shed new light on this much-forgotten nerve, its value as an aid to diagnosis of several diseases and its central role in our daily lives. Objective: We aimed to emphasize how essential and simple clinical examination of the olfactory system can be by highlighting practical techniques and clinical tips for its assessment. We also share pearls and pitfalls in localization and differential diagnosis, which may prove valuable to busy clinicians. Methods: A broad review of the literature was conducted by searching PubMed, Cochrane and Google Scholar for articles and books containing topics regarding examination of the olfactory nerve and its anatomy, physiology and pathology. No particular inclusion or exclusion criteria were used. Results: Forty different works were found, between books and articles, from which 20 were selected after careful analysis. Conclusions: Despite the tragedy and adversity that followed the COVID-19 pandemic, its legacy has taught us a crystal-clear lesson: olfaction should no longer be neglected in clinical practice.摘要 背景：嗅神经（olfactory nerve）从未成为神经科检查的核心项目，恰恰相反，第一对颅神经的检查往往是被忽视的环节。随着新型冠状病毒肺炎（COVID-19）感染继发的嗅觉丧失（anosmia）病例持续增加，2020年的新冠大流行让这一被长期遗忘的神经重新获得关注，凸显了其在多种疾病辅助诊断中的价值，以及在日常生活中的核心作用。 目的：本研究旨在通过介绍嗅觉系统评估的实用操作技巧与临床要点，强调嗅觉系统临床检查的必要性与简便性。同时，我们还将分享定位诊断与鉴别诊断中的关键要点及易犯误区，这对繁忙的临床医师而言或颇具参考价值。 方法：我们通过检索PubMed、Cochrane图书馆及Google Scholar中涉及嗅神经检查及其解剖学、生理学与病理学相关的文章与书籍，开展了广泛的文献综述，未设定特定的纳入与排除标准。 结果：最终共检索到包括书籍与期刊文章在内的40项相关文献，经仔细分析后筛选出20项。 结论：尽管新冠大流行带来了灾难与诸多困境，但其留给我们的教训清晰明确：临床实践中不应再忽视嗅觉功能检查。