Prednisolone does not improve olfactory function after COVID-19: a randomized, double-blind, placebo-controlled trial

Long-term olfactory loss post-COVID-19: Pathobiology and potential therapeutic strategies

An acute loss of smell emerged as a striking symptom present in roughly half of the people infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus in the early phases of the COVID-19 pandemic. In most COVID-19 patients, olfaction recovers over the course of a few weeks. However, a lasting partial or complete loss of smell, often associated with distorted olfactory perceptions termed parosmia, has emerged as a widespread problem impacting at least 5%-10% of those who experience anosmia due to COVID-19. Our inability to offer effective therapies to this hyposmic or anosmic population, comprising millions of patients, highlights an enormous unmet need for the medical system. Here, we summarize the current understanding of the pathobiology causing acute olfactory loss due to SARS-CoV-2 infection, focusing on how the virus interacts with the peripheral olfactory system, a major site of viral infection. We also explore the problem of long-COVID olfactory dysfunction, which may accompany other persistent systemic disorders collectively termed postacute sequelae of COVID-19. Specifically, we discuss an emerging model focused on unresolved immune cell activity driving ongoing dysfunction. Finally, we review current and future therapeutic approaches aimed at restoring olfactory function.

Therapeutic Efficacy of Nasal Corticosteroids in COVID-19-Related Olfactory Dysfunction: A Comprehensive Systematic Review and Meta-analysis

OBJECTIVE

Olfactory disturbance is one of the main symptoms of coronavirus disease-2019 (COVID-19). Various olfactory disorders caused by viral infections are treated with nasal corticosteroids. This study aimed to evaluate the safety and efficacy of nasal corticosteroids in the treatment of olfactory disorders caused by the severe acute respiratory syndrome coronavirus 2.

DATA SOURCES

We searched the Web of Science, Embase, PubMed, and Cochrane Library databases for clinical trials of nasal corticosteroids for treating COVID-19 olfactory dysfunction.

REVIEW METHODS

We assessed the effect of nasal corticosteroids on olfactory function in COVID-19-affected individuals using a Meta-analysis of published studies, considering the number of patients who fully recovered from olfactory dysfunction, olfactory scores following treatment, and olfactory recovery time.

RESULTS

Seven studies involving 930 patients were analyzed. The Meta-analysis results revealed that the olfactory score of the experimental group was 1.40 points higher than that of the control group (standardized mean difference [MD]: 1.40, 95% confidence interval [95% CI]: 0.34-2.47, P < .00001). However, the differences in the outcomes of cure rate (risk ratio: 1.18, 95% CI: 0.89-1.69, P = .21) and recovery time (MD: -1.78, 95% CI: -7.36 to 3.81, P = .53) were not statistically significant. Only 1 study reported adverse effects of nasal steroid treatment, namely tension, anger, and stomach irritation.

CONCLUSION

Although nasal steroid therapy does not result in significant adverse effects, it proves ineffective in the treatment of COVID-19 olfactory dysfunction.

Diagnostic accuracy of the screenings Sniffin' Sticks Test (SST-12) in COVID-19 induced olfactory disorders

Objective olfactory function can be assessed using validated olfactory tests like the Sniffin' Sticks Test (SST). However, their extensive nature makes them less suitable for clinical practice. To address this, shorter olfactory tests like the screenings Sniffin' Sticks Test (SST-12) can be used for screening purposes and reduce testing time. The SST-12 serves as a diagnostic tool for screening olfaction in cases unrelated to COVID-19. However, these screening tests are uncertain regarding their accuracy in detecting olfactory dysfunction in patients with COVID-19 as the plausible cause. We aim to determine the diagnostic accuracy of the SST-12 in adults with post-COVID-19 olfactory dysfunction. We performed a diagnostic accuracy study with data from 113 consecutive COVID-19 diagnosed patients who experienced objectified smell loss ever since. At approximately 6 months after their diagnosis, all participants underwent the SST (reference standard), part of the SST was the SST-12 (index test). Diagnostic accuracy of the SST-12 is measured as negative predictive value (NPV), positive predictive value (PPV), sensitivity, and specificity. The SST-12 detected smell loss in 85 patients among 91 patients with smell loss and ruled out smell loss in 15 patients among the 22 patients without smell loss based on the reference standard. Making sensitivity 93.4% (CI 0.87-0.97), and specificity 68.2% (CI 0.48-0.85). Out of the 92 patients with a positive test result on SST-12, 85 patients had indeed smell loss (PPV 92.4% CI 0.86-0.97), and out of the 21 patients with a negative test result, 15 patients had no smell loss regarding the reference standard (NPV 71.4% CI 0.50-0.88). The findings suggest that the SST-12 holds promise as a useful tool for identifying individuals with smell loss, also in individuals with COVID-19 as cause, but it is important to have a good understanding of the interpretation of the results of the SST-12 when considering its implementation in clinical practice.

Corticosteroids for COVID-19-induced olfactory dysfunction: A comprehensive systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Olfactory dysfunction is a common manifestation in COVID-19 patients and can significantly impact their quality of life. Corticosteroids have been proposed as a potential treatment, but their efficacy remains controversial. This systematic review and meta-analysis aims to comprehensively analyze the efficacy of corticosteroid therapy for treating COVID-19-related olfactory dysfunction.

METHODS

A literature search was conducted in PubMed, Cochrane Library, and Embase databases up to March 1, 2023. Randomized controlled trials investigating the effects of corticosteroids on olfactory dysfunction in patients with COVID-19 were included. The primary outcome was the olfactory score at the end of follow-up, and the secondary outcomes were the duration and the rate of recovery from olfactory dysfunction.

RESULTS

Seven randomized controlled trials with 999 participants were included in the meta-analysis. Compared with the control group, corticosteroid treatment resulted in a statistically significant improvement in olfactory score with a standardized mean difference of 0.55 (95% CI: 0.15 to 0.95). Topical corticosteroids were found to be effective, but systemic corticosteroids were not. In addition, longer durations and higher dosages of corticosteroids treatment may also be associated with significant improvements in olfactory scores. No significant effect was observed on the duration or recovery rate of olfactory dysfunction.

CONCLUSIONS

Our findings suggest that topical corticosteroid treatment is a viable option for improving COVID-19-related olfactory dysfunction, but further research is needed to investigate optimal treatment protocols and safety profiles.

One-year psychophysical evaluation of COVID-19-induced olfactory disorders: a prospective cohort study

BACKGROUND

Olfactory disorders are common in COVID-19. While many patients recover within weeks, a notable number of patients suffer from prolonged olfactory disorders. Much research has focused on the acute phase of olfactory disorders in COVID-19; however, there is still inconsistency regarding the prognosis. We aim to assess both objective and subjective olfactory function in patients with persisting olfactory disorders following COVID-19, 1 year after diagnosis.

METHODS

We objectively measured olfactory function in 77 patients who initially had COVID-19-induced smell disorders, 1 year after confirmed diagnosis. These patients previously underwent two objective measurements at approximately 3 and 6 months after COVID-19, in the context of the COCOS trial (COrticosteroids for COvid-19-induced loss of Smell). The main outcome measurement was TDI score (threshold-discrimination-identification) on Sniffin' Sticks Test (SST). Secondary outcomes included objective gustatory function on Taste Strip Test (TST), self-reported olfactory, gustatory and trigeminal function on a visual analogue scale (VAS) and outcomes on questionnaires about quality of life, and nasal symptoms.

RESULTS

The findings of this study show that 1 year following COVID-19, the median TDI score increased to 30.75 (IQR 27.38-33.5), regarded as normosmia. The median TDI score started at 21.25 (IQR 18.25-24.75) at baseline and increased to 27.5 (IQR 23.63-30.0) at 6 months following COVID-19. The increase of 9.5 points on the TDI score between baseline and 1 year after COVID-19 marks a clinically relevant improvement. Regarding the self-reported VAS score (1-10) on sense of smell, it increased from 1.2 (IQR 0.4-3.0) at baseline to 3.2 (IQR 1.4-6.0) at 6 months and further improved up to 6.1 (IQR 2.7-7.5) after 1 year. Objective gustatory function increased with 2 points on TST a year after diagnosis. Self-reported olfactory, gustatory, and trigeminal functions also improved over time, as did quality of life.

CONCLUSIONS

Objective and self-reported olfactory function continued to improve 1 year after COVID-19. The median TDI score of 30.75 (IQR 27.38-33.5) is regarded as normosmia, which is a favorable outcome. However, the rate of improvement on TDI score reduces over time.

[Persistent olfactory impairment after COVID-19-recommendations of the Working Group on Olfactology and Gustology of the German Society of Oto-rhino-laryngology, Head and Neck Surgery]

This article does not intend to comprehensively review the existing literature on coronavirus disease 2019 (COVID-19)-associated smell disorders, but aims to summarize scientific evidence for otorhinolaryngological practice and provide recommendations for diagnosis and treatment of persistent smell disorders following COVID-19.

Assessment of COVID-19-related olfactory dysfunction and its association with psychological, neuropsychiatric, and cognitive symptoms

Purpose of review

To provide a detailed overview of the assessment of COVID-19-related olfactory dysfunction and its association with psychological, neuropsychiatric, and cognitive symptoms.

Recent findings

COVID-19-related olfactory dysfunction can have a detrimental impact to the quality of life of patients. Prior to the COVID-19 pandemic, olfactory and taste disorders were a common but under-rated, under-researched and under-treated sensory loss. The pandemic has exacerbated the current unmet need for accessing good healthcare for patients living with olfactory disorders and other symptoms secondary to COVID-19. This review thus explores the associations that COVID-19 has with psychological, neuropsychiatric, and cognitive symptoms, and provide a framework and rationale for the assessment of patients presenting with COVID-19 olfactory dysfunction.

Summary

Acute COVID-19 infection and long COVID is not solely a disease of the respiratory and vascular systems. These two conditions have strong associations with psychological, neuropsychiatric, and cognitive symptoms. A systematic approach with history taking and examination particularly with nasal endoscopy can determine the impact that this has on the patient. Specific olfactory disorder questionnaires can demonstrate the impact on quality of life, while psychophysical testing can objectively assess and monitor olfaction over time. The role of cross-sectional imaging is not yet described for COVID-19-related olfactory dysfunction. Management options are limited to conservative adjunctive measures, with some medical therapies described.

Post-viral olfactory loss and parosmia

The emergence of SARS-CoV-2 has brought olfactory dysfunction to the forefront of public awareness, because up to half of infected individuals could develop olfactory dysfunction. Loss of smell-which can be partial or total-in itself is debilitating, but the distortion of sense of smell (parosmia) that can occur as a consequence of a viral upper respiratory tract infection (either alongside a reduction in sense of smell or as a solo symptom) can be very distressing for patients. Incidence of olfactory loss after SARS-CoV-2 infection has been estimated by meta-analysis to be around 50%, with more than one in three who will subsequently report parosmia. While early loss of sense of smell is thought to be due to infection of the supporting cells of the olfactory epithelium, the underlying mechanisms of persistant loss and parosmia remain less clear. Depletion of olfactory sensory neurones, chronic inflammatory infiltrates, and downregulation of receptor expression are thought to contribute. There are few effective therapeutic options, so support and olfactory training are essential. Further research is required before strong recommendations can be made to support treatment with steroids, supplements, or interventions applied topically or injected into the olfactory epithelium in terms of improving recovery of quantitative olfactory function. It is not yet known whether these treatments will also achieve comparable improvements in parosmia. This article aims to contextualise parosmia in the setting of post-viral olfactory dysfunction, explore some of the putative molecular mechanisms, and review some of the treatment options available.