Additive Effects of Interoceptive Training to Physiotherapy in Functional Movement Disorders (interoPTfmd)

Functional movement disorder (FMD) is a common source of neurological disability that imposes a significant financial burden on healthcare systems. However, the heterogeneous manifestations of FMD and numerous associated non-motor symptoms, often fluctuating over time, present a challenge for developing effective treatment pathways. Although increasing evidence supports the efficacy of physiotherapy for FMD, the lack of predictors of treatment outcomes remains a significant obstacle to effectively managing FMD. The main hypothesis of this project is that abnormalities in interoceptive processing are responsible for variability in motor and non-motor symptoms and response to physiotherapy. Interoception describes the afferent signalling, central processing, and mental representation of internal bodily signals. We hypothesize that worse performance on interoceptive tests will be associated with greater severity of motor and non-motor symptoms and worse quality of life. We also expect that patients with worse interoceptive performance and associated non-motor symptoms such as pain will particularly benefit from treatment techniques modulating interoception, such as specific breathing techniques. Therefore, to test our hypotheses, in this project, we will study interoceptive and attentional abnormalities of FMD and identify predictors of the effect of physiotherapy and interoceptive respiratory training.

Functional Neurological Disorder (FND) is a poorly understood and prevalent disorder, making up 16% of outpatient neurology referrals. Patients with functional movement disorder (FMD), which is one of the most common subtypes of FND, are difficult to treat. While growing evidence highlights the effectiveness of physiotherapy for FMD, the absence of reliable predictors for treatment outcomes remains a major challenge in managing the condition effectively.

Our goal is to evaluate the interoceptive profile of individuals with FMD and establish a connection between interoceptive and attentional abnormalities, the type and severity of symptoms, and the response to treatment. The study will utilize the objective clinical and subjective evaluation of symptom severity along with behavioural, neurophysiological, and neuroimaging methods to provide a comprehensive set of measures of interoception and attention. fMRI will further elucidate the neural correlates of interoception and attention. These measures will be analyzed in a cohort of FMD patients and healthy controls to examine the relationship between interoception, attention, and the type, severity, and impact of motor and non-motor symptoms on quality of life.

Interoceptive and attentional measures will also be tested as markers of therapy outcomes in a prospective randomized controlled trial. Eighty FMD patients will be recruited to undergo FMD-specific physiotherapy, with one group receiving additional interoception training via a specific breathing technique (SBTs) protocol. Participants will be randomized to physiotherapy alone or physiotherapy plus SBTs, with clinical outcomes, interoceptive, and attentional measures assessed before and after treatment. This design will evaluate the interventions' impact and identify treatment outcome predictors.

Specific Aims Aim 1: To explore interoceptive mechanisms in FMD and their relationship to symptoms and treatment response.

1.1 Characterize interoceptive profiles (respiroceptive and cardioceptive sensitivity and metacognition) in FMD compared to healthy controls.

1.2 Investigate associations between interoception, motor symptoms, and pain. 1.3 Evaluate interoceptive sensitivity as a predictor of PT outcomes and the impact of SBTs on interoception and pain reduction.

1.4 Examine changes in interoceptive network activation (e.g., salience network) following PT, with or without SBTs.

Aim 2: To study attentional mechanisms in FMD and identify predictors of PT outcomes.

2.1 Assess distractibility as a predictor of PT outcomes. 2.2 Evaluate attentional measures during cognitive, emotional and oculomotor tasks and their relationship to FMD symptoms and PT outcomes.

2.3 Investigate changes in brain activation related to attentional processing and symptom control.

Aim 3: To evaluate the additive effects of specific breathing techniques (SBTs) on physiotherapy outcomes in FMD.

3.1 Compare outcomes between patients receiving PT alone and PT plus SBTs. 3.2 Assess whether SBTs enhance interoception and improve symptoms and HRQoL.

Methods:

Aim 1. Interoceptive sensitivity, metacognition, and attention will be evaluated using psychophysical tasks, fMRI, and eye-tracking to explore their relationship with symptoms and treatment outcomes in FMD.

Aim 2: Attentional mechanisms, including distractibility, will be assessed through clinical tasks, neurophysiological recordings, and fMRI to identify predictors of physiotherapy outcomes.

Aim 3: The effects of SBTs as an adjunct to physiotherapy will be evaluated using clinical scales for motor and non-motor symptoms, alongside quality-of-life and psychological measures.

Eligibility Criteria:
Inclusion Criteria:

* 18 years of age or older
* clinically established diagnosis of Functional Movement Disorder according to Gupta and Lang criteria

Exclusion Criteria:

* age \<18 years
* inability to complete questionnaires because of language difficulties
* severe learning disabilities or cognitive impairment
* major psychiatric or organic neurological comorbidity