Clinical effects of two combinations of olfactory agents on olfactory dysfunction after upper respiratory tract infection during olfactory training

Liu D, A. Müller C, A. Stuck B, Welge-Lüssen A, Hähner A. Olfactory Dysfunction: Etiology, Diagnosis, and Treatment

BACKGROUND

Disorders of the sense of smell have received greater attention because of the frequency with which they occur as a symptom of SARS-CoV-2 infection. Olfactory dysfunction can lead to profound reduction in quality of life and may arise from many different causes.

METHODS

A selective literature review was conducted with consideration of the current version of the guideline issued by the Association of the Scientific Medical Societies in Germany.

RESULTS

The cornerstones of diagnosis are the relevant medical history and psychophysical testing of olfactory function using standardized validated tests. Modern treatment strategies are oriented on the cause of the dysfunction. While treatment of the underlying inflammation takes precedence in patients with sinunasal dysosmia, olfactory training is the primary treatment option for other forms of the disorder. The prognosis is determined not only by the cause of the olfactory dysfunction and the patient's age, but also by the olfactory performance as measured at the time of diagnosis.

CONCLUSION

Options for the treatment of olfactory dysfunction are available but limited, depending on the cause. It is therefore important to carry out a detailed diagnostic work-up and keep the patient informed of the expected course and prognosis.

Study on a Flexible Odor-Releasing Device for Olfactory Training

Olfactory training has been shown to be effective in treating olfactory dysfunction. However, there are hardly any devices that can regularly and quantificationally release odors for olfactory training. A new odor-releasing device, which is low-cost, customizable, semi-automatic, and flexible, was developed in this study. The operation of the device can be easily achieved by the examiner, or even by the participant, simply by pressing a few buttons. A controller system with 15 individual relays was employed to master the working logic for the whole process. The device allows the examiner to isolate from the participants using the Bluetooth module in the control board. The odorants and their concentrations stored in the scent bottles can be customized by the specific requirements of different participants. The odors for training are provided by ultrasonic atomizers, which have simple structures, but powerful features. The flow rates of the odors can also be controlled by altering the rotation speed of the fans. Final experiments on practical odor generation further proved the potential of the developed device for olfactory training. More attention should be paid to the improvements of odor generation devices for olfactory training.

Olfactory training - Thirteen years of research reviewed

The sense of smell is interrelated with psychosocial functioning. Olfactory disorders often decrease quality of life but treatment options for people with olfactory loss are limited. Additionally, olfactory loss accompanies and precedes psychiatric and neurodegenerative diseases. Regular, systematic exposure to a set of odors, i.e., olfactory training (OT) has been offered for rehabilitation of the sense of smell in clinical practice. As signals from the olfactory bulb are directly projected to the limbic system it has been also debated whether OT might benefit psychological functioning, i.e., mitigate cognitive deterioration or improve emotional processing. In this review we synthesize key findings on OT utility in the clinical practice and highlight the molecular, cellular, and neuroanatomical changes accompanying olfactory recovery in people with smell loss as well as in experimental animal models. We discuss how OT and its modifications have been used in interventions aiming to support cognitive functions and improve well-being. We delineate main methodological challenges in research on OT and suggest areas requiring further scientific attention.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Research Progress of Olfactory Nerve Regeneration Mechanism and Olfactory Training

The olfactory nerve (ON) is the only cranial nerve exposed to the external environment. Hence, it is susceptible to damage from head trauma, viral infection, inflammatory stimulation, and chemical toxins, which can lead to olfactory dysfunction. However, compared with all other cranial nerves, the ON is unique due to its inherent ability to regenerate. This characteristic provides a theoretical basis for treatment of olfactory dysfunction. Olfactory training (OT) is one of the main treatments for olfactory dysfunction. It is easy to apply and has few side-effects, and has been shown to be efficacious for patients with olfactory dysfunction of various causes. To further understand the application value of ON regeneration and OT on olfactory dysfunction, we review the research progress on the mechanism of ON regeneration and OT.

Steroids and Olfactory Training for Postviral Olfactory Dysfunction: A Systematic Review

Background: Postviral olfactory dysfunction (PVOD) is a clinical challenge due to limited therapeutic options and poor prognosis. Both steroids and olfactory training have been proved to be effective for olfactory dysfunction with varied etiologies. We sought to perform a systematic review to summarize the evidence of steroids or olfactory training for patients with PVOD.

Methods: A systematic literature review using PubMed, Embase, Cochrane Library, and Web of Science was conducted to identify studies assessing olfactory change in patients with PVOD receiving steroid or olfactory training.

Results: Of the initial 273 abstracts reviewed, 20 articles with data from 2,415 patients with PVOD were included. Treatments including topical steroids, systemic steroids, classical olfactory training (COT), modified olfactory training (MOT), and olfactory training with steroid were analyzed. Both psychophysical olfactory testing and subjective symptom scores were utilized to assess the olfactory function. The routine use of nasal steroid spray alone during the management of PVOD seems to have no positive effect on olfactory dysfunction. Direct injection of steroid or nasal steroid spray into the olfactory cleft significantly improved the olfactory function in patients with PVOD. Olfactory improvement is greater than that of the natural course of the disease with short-term COT. Patients with PVOD would benefit more from long-term COT (>12 weeks). Treatment duration, various odorants, olfactory training devices, changing the types of odors periodically, different molecular odorants, and different concentrations of odorants tended to increase the efficiency of MOT. Clinically significant improvement after olfactory training was defined as an increase of threshold, discrimination, and identification (TDI) score ≥6. From week 24 to week 36, both COT and MOT groups reached the maximum therapeutic effect regarding the number of participants achieving clinically significant improvement. A combination of local or oral steroids with olfactory training is more efficient than COT only.

Conclusion: Olfactory function in patients with PVOD was effectively improved through direct steroid administration in the olfactory cleft, COT, or modification of COT. The addition of topical steroids to COT therapy showed a tendency for greater olfactory improvement in patients with PVOD.

Olfactory Dysfunction in Patients Infected with 2019 Novel Coronavirus

INTRODUCTION

The current study aimed at investigating the occurrence and features of olfactory dysfunction in patients with confirmed coronavirus disease 2019 (COVID-19) infection.

MATERIALS AND METHODS

Patients with laboratory and clinically confirmed COVID-19 infection were enrolled in this longitudinal study. They were managed in either the inpatient or outpatient setting. The demographic, clinical, and outcome data were retrieved from patients' medical records. Olfactory dysfunction features, including the onset pattern, duration, and recovery time were investigated. The visual analog scale (VAS) was utilized as a self-rating subjective measurement of olfactory function.

RESULTS

According to the results, the mean age of the patients (n=502) was obtained at 46.8±18.5 years; moreover, 52.4% and 47.6% of cases were female and male, respectively. It was also revealed that 35.4% and 64.5% of the subjects were outpatients and hospitalized, respectively. Based on the findings, 178 (38.4%) subjects had olfactory dysfunction. The mean values of VAS in hyposmic patients were estimated at 2.5±2.5, 8.3 ±2.1, and 9.4±1.6 at the first evaluation, in 2 weeks, and after 1 month of follow-up (P<0.001). The onset of olfactory dysfunction was more suddenly (58.7%). The majority of cases experienced olfactory dysfunction at the same time as other symptoms 72(51.1%). Based on the results, 0.4% of subjects infected with COVID-19 had olfactory dysfunction as an isolated symptom. The olfactory dysfunction was recovered after 2 weeks in 18 (25.3%) anosmic and 37(46.8%) hyposmic patients.

CONCLUSION

Olfactory dysfunction seemed to be an important symptom of COVID-19 infection. The occurrence of this disturbance as a transient self-limited condition was significantly higher among female subjects.

Olfactory Training for Postviral Olfactory Dysfunction: Systematic Review and Meta-analysis

OBJECTIVE

Olfactory dysfunction is a common problem that is most frequently attributed to upper respiratory infection. Postviral olfactory dysfunction (PVOD) can be prolonged and clinically challenging to treat. Olfactory training (OT) has demonstrated potential benefit for patients with nonspecific olfactory dysfunction. We sought to evaluate the efficacy of OT specifically for PVOD by pooled analysis of the existing evidence.

DATA SOURCES

PubMed, Embase, and Web of Science.

REVIEW METHODS

Following PRISMA guidelines, PubMed, Embase, and Web of Science databases were queried and abstracts screened independently by 2 investigators. We included studies evaluating the efficacy of OT for PVOD and excluded studies evaluating pharmacologic interventions or olfactory loss from other causes.

RESULTS

Of the initial 1981 abstracts reviewed, 16 full-text articles were included. Sniffin' Sticks olfactory testing results were reported in 15 (93%) studies as threshold (T), discrimination (D), and identification (I) subscores and TDI total scores. All studies reported clinically significant results after OT, defined as a score improvement of TDI >5.5. Four studies were included in the meta-analysis, in which pooled estimates revealed that patients with PVOD who received OT had a 2.77 (95% confidence interval, 1.67-4.58) higher odds of achieving a clinically important difference in TDI scores compared to controls.

CONCLUSION

Meta-analysis of existing data demonstrates clinically significant improvements in PVOD associated with OT. Variability exists among OT protocols and may benefit from further optimization. Existing data supports the use of OT for the treatment of existing and newly emerging cases of PVOD.