Study of the Evolution of Olfactory Disorders in Patients With Persistent Loss of Smell Following COVID-19 (ETOC)

The COVID-19 pandemic is a novel medical challenge, particularly because of the systemic nature of this disease. Indeed, COVID-19 affects several organs and systems at once. The brain is affected in several ways: direct infection of nerve cells by SARS-CoV-2, inflammation of the central nervous system, severe systemic inflammation damaging nerve cells, global cerebral ischaemia related to respiratory failure, thromboembolic events related to increased intravascular coagulation and severe psychological stress. As a result, COVID-19 sometimes manifests as neurological and neuropsychiatric symptoms such as dizziness, sleep disturbances, cognitive deficits, delirium, or severe depression.

Sudden loss of smell is a common symptom associated with COVID-19 and SARS-CoV-2 infection of neurons in the olfactory system has been reported in both hamsters and humans. The vast majority of COVID-19 patients recover their olfactory function within a few weeks. However, a significant minority of infected individuals (1 in 5 cases) still suffers from olfactory disorders (anosmia, hyposmia and/or parosmia) several months after the primary infection. These olfactory disorders are frequently associated with depressive behaviour and cognitive complaints. In PET scans, it is even possible to correlate this cognitive dysfunction with hypometabolism of certain brain regions, including the olfactory gyrus.

This project proposes, during one year, to evaluate and follow the evolution of the olfactory capacities of patients suffering from persistent smell disorder since one year (+/- 4 months) following COVID-19. The issue is to study the link between viral persistence in the olfactory sensory organ, chronic inflammation, and central damage to the olfactory system. The follow-up of the evolution of olfactory and neurocognitive capacities, in an integrative way by means of molecular, physiological and behavioural approaches, will inform us on the specificities of "COVID-long" and on the level of peripheral and/or central damage of the olfactory system.

Study Overview

• Status: Completed
• Conditions: SARS-CoV-2 Acute Respiratory Disease
• Intervention / Treatment: Other: Clinical examination; Other: Blood collection; Other: Olfactory evoked potentials; Other: Brushing of olfactory slits; Other: Neurological examination and neuropsychological assessment; Other: Nasal endoscopy; Other: Assessment of olfactory and taste functions

Detailed Description

Prospective monocentric descriptive study. Evaluation of COVID-19 patients with persistent loss of smell during 2 visits at 1 year intervals (V1 and V2).

V1 :The following examinations will be carried out specifically for the research.

• Clinical examination;
• Blood sampling;
• Recording of olfactory evoked potentials;
• Neurological examination and neuropsychological assessment;

V2 :

All examinations performed at V1 will be repeated at V2.

If the following examinations are not carried out during care within 3 weeks of V2, they will be carried out as part of the research during this V2 visit.

• Nasal endoscopy ;
• Assessment of olfactory and gustatory functions.

The following explorations will be carried out:

• Passing of two olfactory and gustatory scales; Olfactory and gustatory disorders will be quantified using two scales, the visual analogue scale VAS and the modified TSS;
• Sniffin Stick test.

In addition, MRI data from clinical care will be collected.

• Study Type: Interventional
• Enrollment (Actual): 30
• Phase: Not Applicable

Contacts and Locations

Study Locations

• France
  • Paris, France, 75010
    • Hôpital Lariboisière

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 55 years (Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Adults < 55 years
• History of symptomatic COVID over 1 year +/- 4 months with a positive PCR diagnosis of SARS-CoV-2
• Olfactory complaint
• Able to understand simple questionnaires in French.
• Subject covered by French Social Security (except for Aide Médicale d'Etat).

Exclusion Criteria:

• Contraindication to nasal swabbing (for morphological reasons, haemostasis disorders, taking aspirin in the 15 days prior to swabbing or anticoagulants, contraindications to the use of a local anaesthetic such as a history of allergy to local anaesthetics or any other reasons judged by the clinical investigator)
• To have been placed in the intensive care unit following COVID-19.
• Known previous nasal-sinus pathology.
• History of psychiatric pathology according to DSM IV criteria, ischaemic, neoplastic, inflammatory, infectious or neurodegenerative (meningitis, encephalopathy, encephalitis, stroke, neurodegenerative disease) known or suspected.
• History of loss of sense of smell prior to COVID infection.
• Patient affiliated to the Aide Médicale d'Etat.
• Person deprived of liberty by judicial or administrative decision, or subject to legal protection.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm

Intervention / Treatment

Experimental: Study population; Adult subjects up to 55 years of age with persistent olfaction disorder after a symptomatic episode of COVID-19.

Other: Clinical examination; The investigator will conduct a clinical examination to rule out other causes of olfactory impairment independent of COVID-19. The investigator will also collect the following information: socio-demographic data (age, sex, blood type, weight, height, etc.), history of olfaction disorder symptoms, past or current treatments received and tobacco/alcohol consumption.; Other: Blood collection; 12ml-blood sample; Other: Olfactory evoked potentials; Olfactory evoked potentials will be recorded during olfactory tests.; Other: Brushing of olfactory slits; collection of olfactory slits cells.; Other: Neurological examination and neuropsychological assessment; MOCA, BREF; CVLT; WAIS IV, MEM III; Right-side and left-side empan, Trail Making Test A and B (TMT), verbal fluency tests, PASAT, Attention Assessment Test; Benton's Line Judgement, VOSP; Assessment of psychological status, fatigue and screening for psychiatric comorbidities: depression & anxiety scales (HAD scale, mADRS depression scale, STAI anxiety scale), Fatigue Severity Scale.; Other: Nasal endoscopy; Nasal endoscopy; Other: Assessment of olfactory and taste functions; scales: VAS and TSS; Sniffin Stick test

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Measurement of olfactory responses by PEO recording and by calculating the TDI score of the Sniffin'stick tests.	To characterise the evolution of the olfactory capacities of patients suffering from persistent odour disorders following SARS-CoV-2 infection over the course of a year.	24 months

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Measurement of olfactory perception threshold, olfactory discrimination capacity and odour identification.	Describe the olfactory performance	24 months
To characterise the persistence of SARS-CoV-2 in the olfactory epithelium.	Characterisation of the presence of SARS-CoV-2 by PCR in the olfactory mucosa.	24 months
To characterise any damage to the olfactory nerve	Mapping analysis of the olfactory nerve of COVID-19 patients by MRI tractography technique.	24 months
To identify the presence of inflammatory markers in patients.	Measurement of cellular and inflammatory markers in the olfactory mucosa.	24 months
Detection and measurement of markers of neurological disorders in the blood.	To identify the neurological damage in patients.	24 months
Measurement of patients' cognitive performance by neuropsychological assessment (standardised tests).	To identify possible cognitive abnormalities in these patients with prolonged loss of smell.	24 months

Collaborators and Investigators

• Sponsor: Institut Pasteur
• Collaborators: Hopital Lariboisière
• Investigators: Study Director: Pierre-Marie Lledo, Prof., Institut Pasteur

Study record dates

Study Major Dates

• Study Start (Actual): June 20, 2022
• Primary Completion (Actual): October 15, 2024
• Study Completion (Actual): October 15, 2024

Study Registration Dates

• First Submitted: November 23, 2021
• First Submitted That Met QC Criteria: November 23, 2021
• First Posted (Actual): November 24, 2021

Study Record Updates

• Last Update Posted (Actual): May 14, 2025
• Last Update Submitted That Met QC Criteria: May 12, 2025
• Last Verified: May 1, 2025

More Information

Terms related to this study

• Keywords: Neuroinflammation; coronavirus; evoked potentials; olfaction disorder
• Additional Relevant MeSH Terms: Neurologic Manifestations; Nervous System Diseases; Sensation Disorders; Olfaction Disorders; Anosmia; Respiratory Tract Diseases; Respiration Disorders
• Other Study ID Numbers: 2021-006; 2021-A02419-32 (Other Identifier: ID-RCB)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No