Central Processing of Odour Stimuli in Patients With Functional Somatic Disorder, MCS or Post Covid Compared to Healthy Controls

Condition(s) studied

Investigational drug(s) / intervention(s)

MRI and paraclinical tests: The patients and controls will be evaluated using MRI and furthermore a large test battery of questionnaires and paraclinical tests. Including the following test: MCS checklist, BDS-Checklist, Symptom Checklist-92 (SCL-92), Whiteley-8, SF-36, Major Depression Inventory (MDI), GAD-10 anxiety scale, and related questionnaire, behavioral olfactory test (TDI), habituation test, pain measurement thresholds tests, Heart Rate Variability and cognitive testing.

Study summary

Background:

Functional somatic disorders (FSD) are frequent in all medical settings and characterized by persistent physical symptoms that cannot be explained by other somatic or psychiatric conditions. In recent decades, a number of different types of functional somatic disorders have been defined, but so far there is no clear explanation for the pathophysiology.

The high prevalence of olfactory problems in some patients with FSD suggests that olfactory symptoms are a potential diagnostic biomarker, especially in patients with multiple chemical sensitivity (MCS) and/ or post-covid.

The olfactory system is a unique sense with direct pathways to the limbic system, which is associated with emotion and mood. The focus on the olfactory system has revealed a significant association of this sense with numerous diseases.

Hypotheses:

* Patients with MCS and FSD have normal olfactory tests (normosmic subjects according to TDI score using "sniffing test") but differ in habituation test compared to healthy controls.
* MCS, post-covid and FSD patients have different odour perception processing in the brain as a "fingerprint" of functional somatic disorder compared to healthy controls.

Research plan:

The aim of this parts of the study is to identify specific MRI and paraclinical measures for MCS, post covid and BDS. In the first phase, 5 patients with MCS and 5 healthy controls will have a full clinical test of the olfactory system at the Flavour Institute, AU. In addition, they will be scanned (for "fingerprinting") where the investigators expect to find changes in olfactory connectivity similar to those seen in depression. This phase of the study will lead to a conclusion on the exact MR parameters to be used in the main study. In the second phase of the study, 10 patients with MCS, 10 with post-covid, 10 with FSD, and 10 healthy controls will be evaluated using a test battery of questionnaires and paraclinical tests.

Perspectives:

Previous imaging studies have focused on pain stimulation paradigms, rest-state fMRI, and DTI, but the olfactory system may be the "missing link" in identifiying a quantitative candidate in terms of whole-brain computational modeling and could potentially be used as a "fingerprint" in diagnosis and treatment monitoring.

Eligibility

Primary outcome measure(s)

• "Fingerprinting" — Through study completion, an average of 6 months
  The investigators seek to employ whole-brain computational modeling based on MRI-derived functional and structural connectomes. The investigators will use the 3T MR Siemens® scanner that is situated at Aarhus University Hospital. A T1 structural image sequence will be run to obtain an image for later co-registration. After scanning data analyses including pre-processing, first-level analyses, and higher-level analyses will carry out.
• "Sniffing Stick test" — Through study completion, an average of 6 months.
  The standardized psychophysical olfactory test, the "Sniffing Stick" test; will be performed on all three groups of participants before the scanning session. This battery of tests consists of odor threshold (T), discrimination (D), and identification (I) parts. The total score (TDI) was determined by the sum of the three scores (T+D+I). Habituation test; In order to test the flexible hedonic evaluation of odors in MCS and BDS compare to healthy controls the investigators will carry out habituation tests. The evaluation task asks the participant to rate the odors pleasantness, all individuals responses will be arranged by Likert scale 1-5.

Trial sites (1)

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