Scent & Sensibility: A journey towards recovery in COVID-19 induced olfactory disorders

Abstract

Our sense of smell is a powerful yet often overlooked sense, and plays a crucial role to various facets of our lives including overall well-being, social interactions, emotions and memory. The COVID-19 pandemic has thrust this sense into the spotlight due to the significant number of individuals experiencing smell loss. However, healthcare providers are faced with the challenge of addressing this issue effectively, lacking comprehensive guidance in managing patients with COVID-19-induced smell loss. This thesis aims to fill this gap by providing a thorough examination of the diagnosis, treatment, epidemiology, and clinical course of COVID-19-induced smell loss. Chapter 2 delves into the diagnostic accuracy of the Sniffin' Sticks Test (SST-12) as a screening tool for olfactory disorders, but not yet validated for smell disorders caused by COVID-19. While the validated extended SST are effective, their lengthy nature limits their practicality in routine clinical settings. We evaluated the SST-12's potential as a shorter screening tool and found promising results, suggesting its utility in detecting smell loss induced by COVID-19, albeit with the need of careful interpretation by healthcare professionals. Building upon the hypothesis of COVID-19-induced inflammation affecting the olfactory nerve, Chapter 3 & 4 outlines the COCOS trial, a rigorous investigation into the efficacy of prednisolone in treating COVID-19-induced smell loss. Despite earlier promising indications, our randomized, double blinded, placebo controlled trial revealed no significant difference between prednisolone and a placebo in improving olfactory function, prompting a cautious approach to prescribing prednisolone for persistent smell disorders post-COVID-19. Chapter 5 explores the potential benefits of olfactory training in COVID-19-induced smell loss through a case-control study, indicating statistically significant but not clinically relevant improvements in olfactory function with training. However, further research through randomized controlled trials is recommended for definitive conclusions. In Chapter 6, we observe continued improvement of smell disorders one year after COVID-19, albeit at a slower rate, underscoring the long-term impact of COVID-19 on smell function. Finally, Chapter 7 presents a longitudinal cohort study comparing the incidence, severity, and duration of smell and taste loss in COVID-19 versus non-COVID-19 cases. We observerd a higher incidnence and severity in COVID-19 cases, but a longer duration of having symptoms in non-COVID-19 cases. In conclusion, this thesis provides a comprehensive understanding of COVID-19-induced smell loss, from diagnosis to long-term prognosis, emphasizing the need for continued research, awareness, and support for individuals affected by this debilitating condition, regardless the origin of their smell loss.