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NCT Number: NCT05421221

Olfactory Training in COVID-19 Associated Loss of Smell

Olfactory dysfunction (OD) like hyposmia or anosmia has been realized as a common symptom or even cardinal sign of the disease and can be persisting after recovering.

There are two different hypotheses on the pathogenesis of OD in past COVID-19: The central hypothesis, which speculates on neurotrophic abilities on olfactory receptors in the neuroepithelium, and the peripheral hypothesis, which speculates on damage of the sensory olfactory epithelium.

Potential treatment strategies aim for the unique neural plasticity of the olfactory system and its potential for recovery.

Clinical studies and case reports have shown a promising effect of olfactory training (OT) by frequent sniffing and/or exposure to odors 2-4 times a day for several weeks.

The main objective of the study is to assess the effects of olfactory training in patients with COVID-19 related OD on:

1. objective olfactory testing with the Sniffin' sticks test (identification and discrimination), 2. subjective OD and its impact on the daily life, 3. other clinical scales and questionnaires referring to OD-related mood and quality of life, 4. gender differences in COVID-19 related OD. Approach / methods OT will be performed twice a day with a 4-odor training set for 12 weeks. Effects of OT on COVID-19 related OD will be measured with objective and subjective efficacy variables.

The sense of smell is an important function for social relationships and is therefore a challenging clinical problem with few proven therapeutic options.

With this new approach, we want to investigate a possible simple treatment for an impedimental symptom of COVID-19, but also learn more about the pathomechanism of post-infectious OD.

To our knowledge, this will be the first study comparing patients with COVID-19 associated OD with and without OT in clinical outcomes.

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Key information

Conditions

COVID-19 Anosmia Coronaviridae Infections Coronavirus Infections Hyposmia Infections Lung Diseases Nervous System Diseases Neurologic Manifestations Nidovirales Infections Olfaction Disorders Pathological Conditions, Signs and Symptoms Pneumonia Pneumonia, Viral RNA Virus Infections Respiratory Tract Diseases Respiratory Tract Infections Sensation Disorders Signs and Symptoms Virus Diseases

Age range

18 year and older

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Medical University of Innsbruck

Innsbruck, Tyrol, 6020, Austria

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • The subject is aged over 18 years;
  • confirmed diagnosis of COVID-19 at least three months ago (history of positive PCR-testing required) or positive serum nucleocapsid antibody titer against SARS-CoV2;
  • post-infectious COVID-19 related olfactory dysfunction persisting for at least three months with abnormal Sniffin' sticks test (<13/16 items correct in the identification part);
  • the patient is willing to undergo odor training over 12 weeks;
  • written ICF is obtained.

Exclusion criteria

  • History of olfactory dysfunction prior to COVID-19 infection due to other conditions e.g. status post traumatic brain injury, Parkinson's disease, allergic rhinitis, etc.;
  • Nasal pathology not related to COVID-19 in the systematic otorhinolaryngological examination including endoscopy.
  • the participant is pregnant

Treatment and study plan

Sniffin' sticks Duftquartett

Device

4-odor training set over 12 weeks with Sniffin' sticks "Duftquartett"

Primary outcomes

  1. primary endpoint

    Time frame: 12 weeks

    changes between groups from baseline to week 12/termination visit regarding correct odor identification and discrimination

Secondary outcomes

  1. Visual Analog Scale

    Time frame: 12 weeks

    from 0 to 10, higher score means better subjective olfaction

  2. Short-Form-36 Health Survey Questionnaire (SF-36)

    Time frame: 12 weeks

    Quality of Life Each domain is scored from 0 to 100, higher scores mean better health status

  3. Mood inventory

    Time frame: 12 weeks

    Will be applied in German

  4. Hospital Anxiety and Depression Scale

    Time frame: 12 weeks

    Anxiety and Depression Each item is scored on a 4-point scale from 0 to 3; lower scores mean less anxiety/depression

  5. Patient Progress and treatment response over time

    Time frame: 12 weeks

    Using Patient Global Impression of Improvement

  6. Clinical treatment response over time

    Time frame: 12 weeks

    Using Clinical Global Impression of Improvement

Sponsors and collaborators

Lead sponsor

Medical University Innsbruck

Other

Registry information

Official study title

A Randomized Controlled Trial of the Effectiveness of Olfactory Training on Loss of Smell Related to COVID-19 (SMELL)

Important dates

Study start
2022
Primary completion
2024
Study completion
2024
First posted
Jun 16, 2022
Registry last updated
Apr 23, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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