Olfactory nerve: from ugly duckling to swan.

Sofia Mermelstein,Paulo De Lima Serrano,Rachel Alencar De Castro Araújo Pastor,Victor Evangelista Rodrigues Pereira,Abelardo Queiroz Campos Araujo

doi:10.1590/0004-282x-anp-2020-0529

Sofia Mermelstein, Paulo De Lima Serrano + Show 3 more

Open Access

https://doi.org/10.1590/0004-282x-anp-2020-0529

Copy DOI

Abstract

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. 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. 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. Forty different works were found, between books and articles, from which 20 were selected after careful analysis. 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.

Highlights

Different, as primitive as it is sophisticated, the olfactory system does not play by the book
Olfaction does share similarities with other parts and properties of the human body, as it may benignly lose its function with age or reveal life-threatening organic diseases, intracranial lesions, systemic disorders or neurodegenerative conditions[1]
Check whether there is any kind of nasal congestion that could potentially alter adequate evaluation of olfactory nerve (ON) function (Table 3) and search for signs of trauma or other macroscopic alterations such as polyposis and deviated septum

Summary

INTRODUCTION

Different, as primitive as it is sophisticated, the olfactory system does not play by the book. Patients with olfactory deficits often present with complaints of either loss of or diminished sense of smell (or even altered discrimination of different odors), this is not always the case. The absence or presence of spontaneous clinical complaints regarding loss of olfaction does nothing to absolutely exclude or confirm the existence of smell dysfunction Another (often forgotten) caveat is that most patients who do complain of anosmia suffer from bilateral olfactory lesions. Check whether there is any kind of nasal congestion that could potentially alter adequate evaluation of olfactory nerve (ON) function (Table 3) and search for signs of trauma or other macroscopic alterations such as polyposis and deviated septum These could steer the diagnosis towards a conductive cause for anosmia/ hyposmia. Until this matter is settled, we advocate for the latter technique

Key points during neurological examinations

Findings

KEY POINTS