Thesis defence : Séphora MINJOZ

Under the supervision of Sonia Pellissier and Pascal Hot

Somatic symptom disorders [SSDs] encompass a broad spectrum of physical symptoms or complaints that are not attributable to an organic dysfunction or lesion, even though they cause marked suffering or have a significant functional impact. These disorders are generally considered to be idiopathic pathologies with a multifactorial bio-psycho-social causality. Some recent models suggest that one of the neurobiological systems involved in stress, the autonomic nervous system, may be disrupted. With this in mind, the first objective of this thesis was to characterise the functional autonomic state of two different forms of SSD: irritable bowel syndrome and psychogenic non-epileptic seizures, in relation to cognitive-emotional vulnerability. Following an initial study designed to validate the effects of repetition of a mental load task (study 1), we conducted two studies which enabled us to demonstrate the existence of dysautonomia (i.e. autonomic functional abnormalities) in SSS (study 2) and the existence of significant psychological distress in these disorders (study 3).

The dysautonomia was particularly visible in reactivity to a mental load task, underlining the need to assess autonomic flexibility. Our results also enabled us to validate the value of looking for autonomic endophenotypes (i.e. individual autonomic profiles) to better characterise resting tonic dysfunctions of the autonomic nervous system in SSD. We were thus able to identify 'atypical' autonomic profiles in patients, offering the prospect of sub-classifying disorders to complement standard classification systems. These initial encouraging results need to be confirmed by a more systematic characterisation of dysautonomia in the different forms of SSD. The second part of this thesis involved evaluating the efficacy of heart rate variability biofeedback [HRV-BFB] techniques targeting the autonomic nervous system to reduce dysautonomia and associated emotional deficits. We felt that these techniques were particularly promising because they could be incorporated into the general principles of the biopsychosocial approach to care. Initially, we sought to experimentally validate the clinical and physiological efficacy of this non-medicinal technique in the general population (study 4), using an approach based on scientific evidence. Our results enabled us to validate the clinical effectiveness of this method compared with a placebo technique. We therefore applied the protocol to our clinical populations in order to study its psychophysiological effects (study 5). A major result was the replication of the clinical effects of VFC-BFB observed in the general population in TSS patients. VFC-BFB therefore appears to be a therapeutic tool of interest in these disorders, particularly in the management of psychiatric comorbidities. Our work also provides elements for discussion on the physiological mechanisms of action underlying the efficacy of this technique and suggests avenues for a more individualised approach to these methods. The results of this second part of the thesis will need to be replicated, but are promising. They provide experimental validation, using an evidence-based medicine approach, of a non-medicinal intervention, which addresses the main limitation reported in the literature, and offer new prospects for complementary management of SSD.

Keywords: Somatic symptom disorders, irritable bowel syndrome, psychogenic non-epileptic seizures, autonomic nervous system, stress, heart rate variability, cognitive-emotional vulnerability, biofeedback